Carb Synchronization

I know there's about a million posts here on carb synchronization but I've checked the other posts and I can't seem to find an answer to this question. I just took apart and cleaned my friend's carbs on his 1993 XJ600 Seca II, from top to bottom. Needles, seats all the seals and gaskets, floats, jets, pilot screws, etc... I put the carbs back together according the factory specs in the Haynes manual. Put them back on the bike, started right up. Got my sync gauges out, synced 1 & 2, then 3&4, then bank 1 to bank 2 by syncing 2 & 3. 1 & 2 synced fine, 3 & 4 synced fine. 2 & 3 were not even close and I couldn't get them close. I'm not sure what could be causing it. She also idles kinda rough but I think its the mixture screws. I may have set them too lean. Did 2 turns out. I've heard 2 or 2 and a half so I figured I'd try 2 to start. Not sure that has anything to do with it but I figured I'd mentioned it. If anyone has any hints, tips, comments, or whatever or if I left any crucial information out let me know. Thanks guys.

 

If the valves clearance is not in spec it will never correctly sync. Hope this helps.

Gary H.

 

If the valves clearance is not in spec it will never correctly sync. Hope this helps. +1
Vacuum leak, shaft seals.
Oring missing or not in order on pilot screws..

 

When you say o ring not in order on pilot screws, what does that mean?

Edit: I think I got it. You mean the oring, washer, spring order? If that's it, I'm positive they're all correct. Now as far as the o rings being worn, I could probably use new ones. Know where to get any?

 

message member Chacal. He operates a parts warehouse with about every part you could need for these bikes.
He is fair and honest and has a wealth of information on these bikes.

http://www.xjbikes.com/forums/index.php?forums/xj4ever-supporting-vendor.23/

hope this helps

 

could the idle knob be holding 3/4 so far open 1/2 cant keep up? back off the idle and see if you can get them closer. I start the mixture screws at 2-3/4

 

I tried the ide screw at different points when I was synchronising them. Didn't make a difference. The two banks were so far out of wack. No luck. Now it's all back together and I get the idle screw just to around 1400 rpms. If I go just a hair further, she jumps up to 25oo - 3000 and stays there. Then back the idle screw off just a hair and she's back down to 1400 or so. I think it's a vacuum leak with the boots. I'm going to check them and back out the mixture screw a bit as well. I think 2 turns out is too lean.

 

did you replace the throttle shaft seals? Better question, did you dip the carbs in cleaner or solvent? If you did, all the rubber seals and Orings will need replacing..

 

Two turns out is too lean. But that may not matter, at least not right now.

You didn't answer the following IMPORTANT questions:

Are the valve clearances in spec? Yes or no? If not, you are wasting your time.

Did you "dip" or submerge carbs that still had the butterflies/shafts still in them? Yes or no?

New question: did you wet-set the float levels? WET set, not "they look OK."

You appear to be trying to "shortcut" the process of getting the carbs tuned. It won't work.

Answer the above so we can help, please.

 

Yea. You're right Fitz. I was trying to get out of half the work that needs to be done. I'm just doing it. I'm not doing it "right". No excuse but I'm just trying to get the bike running as good as possible until I have the time to take everything apart and do it right. But here are the answers to your questions anyway.

Valve clearance? Ihave no clue. Never even pulled the valve covers to check. I honestly don't remember if Itook out butterflies when I dipped them. I don't think I did.
Float levels were set when I had them apart and then checked again when they were on the bike. Not sure what "WET set" means.

 

Like the others said, check the valve clearance.

Wet Set means measuring the fuel level with fuel in the carb (with a clear tube in the float bowl drain), as opposed to flipping the carb over and measuring the height of the float (when the carbs are "dry").

What is the idle on the XJ600 SecaII? Your sync won't really mean anything if you are even a little off idle speed. If syncing brings up the idle speed (because a higher idle position compensated for the off-sync), lower the idle and continue syncing. Same goes for colortuning if you are doing that too.

The fact that a slight adjustment in the idle screw is causing the engine speed to jump says to me that the pilot circuit on one or more of the carbs is not actually contributing enough fuel, and the others are having to compensate by being opened past pilot circuit. This can be caused by either because of an air leak in the venturi, air leak in the pilot hole, because the sync is still way off (pilot hole is still covered by butterfly), or because there isn't enough fuel flow in the pilot circuit (clogged passages or fuel level).

If you dipped the carbs without removing the butterflies and throttle shaft seals, you very well could have an air leak there too. You have to break the rack (separate the carb bodies) to do so.

Basically, if you want to run the bike well, you have to do all of the steps, or you will be chasing your tail, trying to diagnose "one" problem that could be the result of several failures (in this case, valve adjustment, throttle shaft seals, pilot o-rings, in addition to fine tuning the pilot mixture screws, sync screws, and idle adjustment).

 

Ok. I did do the WET set after I got the carbs back on the bike. Everything was good there. I did break all four carbs apart when I was cleaning them but, I don't think I removed the butterflies so that might be one issue. I'm almost positive of two things. My pilot screws are set too lean AND there's a vacuum leak somewhere. I will, in the near future pull the valve covers, as I have the carbs off to replace those shaft seals, and check the clearences and order shims as needed. I also have to get one of those valve spring tools. I'll probably purchase some new pilot screw o rings just for safe measure. I've already replaced the needles and seat o rings, which were causing gas to pour out of the overflow tube on one bank so I'm good there. I'm sure I'll get myself into more trouble as I go along. All part of the learning process. I'm just thankful for boards like this with knowledge people to ask for advice.

Thank you guys for the help.

 

are you in brooklyn by chance?

 

The carbs actually have to be wet set off the bike on a flat level holder per the manual. I would be interested in how you adjusted the floats on the #2 and #3 carbs on the bike as you have to remove the bowls to do the adjustment to the float tang.

This is once facet of restoration of the bike that has no short cut or quick and easy fix. The carbs have to be methodically torn down, hand cleaned, rebuilt and adjusted in order.

these will help you..

http://www.xjbikes.com/forums/index.php?threads/in-the-church-of-clean.14692/#post-424352
http://www.xjbikes.com/forums/index.php?threads/the-secret-life-of-carburetors.14751/
http://xjbikes.com/forums/index.php?threads/airhead-valve-adjustment-with-pics.14827/

Again, all is for naught without the valves being in spec. Also a compression test after the valve adjustment will tell you if you have a viable plant or not.

These bikes reward precision and anything else will cause nightmares, swearing, frustration and repeated attempts at half repairs

 

Used to be. Born and raised in Greenpoint\Williamsburg. Moved to Charlotte about 6 years ago.

 

Understood.

As far as adjusting the floats on 2 and 3, I set them when they were off the bike and then checked them again when the were on the bike by removing the float bowl screw and having a clear length of tubing attached to the drain. Making sure the fuel level was at the line on the float bowl cover.

Nightmares, swearing, frustration and repeated attempts is putting it mildly.

 

IIRC, the shop manual tells you to measure the fuel height on the bike, with the bike level, and you have to measure at the side of the carb rack right in the middle for it to be accurate. Then remove the rack (like pepNYC did) to adjust the floats.

We level them on a separate apparatus because it just makes the process easier. The manual's process really is more of a "check," if there's lots of adjusting to do then it becomes more difficult.

 

I may be wrong - but I thought the fuel level is supposed to be 3mm below the float bowl 'seam'.
+/- 1mm

 

If that's true I definitely have them set too high. I'll check my manual again. Thanks.

 

You did.

This is better than the manuals: http://www.xj4ever.com/setting fuel levels.pdf

And again, unless the valves are in spec, you can't effectively tune the carbs.

 

Ok. I took the plunge. Pulled the carbs back off and pulled the valve cover. Thought I had a feeler gauge but I couldn't find it so as soon as I can get to the store to buy one or borrow one I'll check the valves out. But...in the meantime, I want to ask you guys something that I noticed. Before I pulled the carbs I was checking for a vacuum leak and I remember back in the old days when I used to work on cars a good way to check was to put your hand over the choke, if there was a leak somewhere the car would still run because it was still pulling air in from somewhere. If it died, there was a good chance there was no leak or a very small one. So, I did that on the bike. Covered each one. When I covered carb number one nothing, bike kept running, no difference. Same for number two, no difference. However, when I covered three, the bike stalled and same for number four. Covered it and the bike stalled. So then I went to the little vacuum ports on the manifold where you hook up your sync gauge. I noticed hardly any vacuum on one and two cylinder. Three and four were nice and strong. Hence the major difference on the gauges between 2 and 3. Now my question is, could the valves being so out of adjustment cause that or is it possible I do have a vacuum leak somewhere? I'm hoping and praying that the rings are not shot on the one or two cylinder thus causing the weak vacuum. She doesn't burn oil but who knows. What do you guys think? Let me know if I left out any info. Thanks.

 

Finish with the valves, then do a compression test. That will answer the question whether or not your engine is healthy.

I'm not sure your test works on these bikes because air has to flow into the back of the carbs to pick up fuel. Air leaks further down the line wouldn't mix with any fuel, so I imagine the cylinder would stumble either way UNLESS your enrichment circuit was open and dumping in fuel. Remember that there is no "choke" on these carbs.

Usually, air leaks are tested by adding "fuel" in the form of unlit propane, around the intake boots and carb bodies. If the engine speed changes, then it is sucking up that propane.

It could just be that your butterflies on 1/2 are completely closed, so you wouldn't feel any vacuum and 3/4 stumble because they are the only two limping the engine along. Do a "bench sync" of your carbs, since they are already off. Look at the engine side of the of the carbs and find the tiny holes that are covered by the butterflies. The proper idle position is one hole partially covered. visually compare 3/4 to 1/2 and note if there are any differences.

 

I'll be checking the valves this week sometime. I'll probably need your guys help with that as well. I'm seeing a lot of conflicting opinions on how to correctly check the clearance. Some say lobe at 180 degrees and some say the lobes should be facing away from each other. I have the haynes manual and it says lobes away from each other. I know they're supposed to be at TDC when you check them but is it when the lobes on each cylinder are facing away the piston is at TDC?

Back to the carbs. Few questions. When you say air has to flow into the "back" of the carbs. Where exactly is it drawing the air in from?

Also, when you say "enrichment circuit" you mean what? The little knob you pull on startup to let more fuel in? I looked at those holes when I had the carbs apart and it seemed like it was opening and closing those holes properly.

I actually did the opposite of what you said about the propane. I sprayed carb cleaner around the 1 and 2 carbs to see if the engine would bog. Nothing. Even if I spray it right in the carb, no difference. If I spray it directly in 3 or 4 carb she bogs down and then eventually smooths out again. But, if I spray it in the vacuum port on the 1 and 2 manifold where you check the sync, the engine revs up.

I'll take a look at how to do the bench sync. I know I saw a few videos on it.

Thanks

 

Just some friendly advice...it seems your doing the whack-a-mole attempt at getting the bike to run correctly like I and many have. When I checked the valve clearances on my bike, I set aside about half a day and took my time. The only way that you can figure out what shim you will need to put the valve clearance in spec is to know what shim is in the bike already. That is printed on the bottom of the shim and you have to remove the shim to identify it. I would check the clearance, then using the zip tie method, pull the shim, record the number, replace the shim and then go on to the next. Now I have a permanent record of what shims are in the bike so next time I just have to check clearances.

Once you have the valves clearances in spec, then do a compression test and verify that engine does not need more work.

If the compression test is good, then onto the carbs.

Again...these are little precise requiring gadgets...

Do yourself a big favor and tear them down all the way and off the rack. Get a full rebuild kit and replace all the throttle shaft seals, fuel rail seals, float valves. a/f o-rings...

Seriously, the Church of clean is a perfect guide to walk you through the proper and complete cleaning of the carbs. Many little hidden areas that need attention due to 30 years of age, buildup and dirt/varnish and corrosion.

Once reassembled then onto the bench syncing the butterflies, wet setting the floats on a carb stand to spec.

New plugs, new vacuum caps, and the bike should start right up. Then a running vac sync and finally a colortune and you will be pleased with the results.

Truthfully, and with all good intentions, there is absolutely no other way to do this right. Many have tried, including me, and you just end up redoing work and eventually doing it the way that is prescribed in the forums.

 

Bruce, I understand. I fully intend to take my time, pull the shims and figure out what I need. The compression test I was going to skip because thinking back, this bike ran great last year and the carbs synced perfectly after I took them apart (totally off the rack) and cleaned them and replaced the seals. It sat all winter so I wouldn't think the rings would be bad from sitting. I don't have a compression tester anyway. If it is the rings, I'm not going in that deep so it will just have to run on two cylinders or I'll sell it to someone who wants to tear it apart and change them. I completely understand what you're saying though. However, ya need to have the right tools to do the job right but I really don't have a lot of money to spend on colortunes, compression testers, valve shim tools, etc... I'll have to make due with what I have and can afford for now. What I do intend to do is check the valves and get the carbs cleaned up again but in order to do that I was just trying to find out some info about the cam lobes because of the conflicting opinions. Also, some other info on the carbs so I fully understand how they work, not just how to rebuild them. Where it sucks in the air, how to bench sync, wet set the floats, etc...which I will be doing after I get them back together. I have sync gauges so I'll be using those to do the dynamic sync when the time comes.

I'm trying to do the best I can with what I have to work with. I'm actually hoping it will work out as to where I can just swap some shims around and won't have to buy many. If I had more money I'd get rid of this thing and just get a newer one but unfortunately that's not the case. I don't mind tinkering, it's the expense I can't deal with. These parts are friggin expensive for this bike. Geez.

Please don't take any of this as disrespect as I value yours and everyone else's opinion here and I truly appreciate the help and advice.

 

The tools to adjust valves are not that expensive, feeler gauges, hold down tool (it's like $15), and a inch-lb torque wrench from harbor freight (for the valve cover bolts) will set you back less that $50 total. You can rent the compression tester. Add to that the valve cover gasket and donuts (or you'll have oil leaks, penny wise, pound foolish), and any shims that you need to replace (after swapping some around). I know it probably seems like a lot now, but there is just no way around this basic maintenance to get it running in any reliable fashion. It's not different than an oil change, brakes, tires, battery (and you are going to go through those too right?). Bigfitz52 always quotes an expectation of $600-$800 in parts to get the bike reliable. I doubt there are any motorcycles out there that are any less expensive to recondition.

Your test that you mention involved covering the "choke". These bikes don't have a "choke." A choke is a butterfly valve on the airbox side (what i called "back" of the carb in my reply) of the carb which restricts, or "chokes" the airflow into the carb in order to enrich the mixture for starting. These carbs enrich the mixture by dumping more fuel in. Basically, the test you mentioned doesn't really tell you much about the performance of 1/2.

If a cylinder is running lean, more fuel should result in the rpm increasing. If fuel in the intake causes it to bog down, with no initial surge, then you are not running lean. Furthermore, if you add carb cleaner to the intake, and nothing happens, then unless you have a dead cylinder, your butterflies are still completely closed, there is simply no air flow through that carb (i.e. your sync is still WAY off between 1/2 and 3/4).

I don't think any of your tests say definitively that there is any engine problem. The ONLY way to determine that is a compression test, and valves out of spec can throw off you compression test, so you have to do that first.

Finally, the cam lobe should point away from the shim bucket. A few degrees off one way or another simply doesn't matter, it's round on that end.

If you don't have the funds to do the valves and compression test now, stop tinkering until you do. I don't mean any disrespect by that, but it's just the fact of the matter. Why keep tinkering and being frustrated about a bike that "could" have a dead cylinder? Test and find out or put it away until you can.

 

I actually have the feeler gauges, magnet and the torque wrench. I was figuring I could use the "zip tie" method Bruce mentioned instead of buying the hold down tool I'll probably only use once. I didn't take the valve cover gasket into account. I see one on ebay for about $30 shipped. But yes, that is exactly what I had planned. Valves, then carbs. Maybe I can find someone that has a compression tester I can borrow.

It does sound like the butterflies are staying closed. I'll have to check that. How that heck can they be THAT out of sync? What else might cause the butterflies to stay closed on that one bank? Or is it only the sync screws?

So the lobes should point opposite from each other, facing the outside of the engine correct? Then check both intake and exhaust valves on that cylinder in that position? Then when I move to the next cylinder, same thing? Cam lobes out and check each valve?

I still need to figure out if these floats are set right as well. I have to go over that PDF Fitz sent.

No disrespect taken. Yeah, I'll be taking it off the road this winter to finish the repairs. Thank you.

 

The cam lobe needs to point away from it's respective shim bucket. You measure one valve at a time, I typically did the intakes, then the exhaust. Just measure one, rotate the crank 180 degrees, and measure another (obviously they won't be in 1-2-3-4 order, more like 1-2-4-3 or 1-3-4-2 I don't remember which).

If you broke the rack, maybe you reassembled the throttle linkages incorrectly? Only the linkage, including the sync screws, can affect the butterfly positions. You should take a picture of the engine side of the bank and maybe we can see if something is amiss? Did you take pics of the assembly before disassembling for reference?

 

When you bench sync the carbs you will realize how darn precise they have to be..It really doesn't take much to have them off a bit.

I understand budgets...and find the large zip tie to do the valve clearances. Also Member Hogfiddles runs a shim pool where he will exchange shims for free, however you do need to provide a deposit. Many people rush the carb and valve shim that end up frustrated, get rid of the bike and never visit the forums again. That is the dark side of these bikes..lol.. we are here to help as much as we can. A couple of the wizards here have more knowledge and experience in their thumb than most of us do in our entire being.

Auto stores often offer free use of or rental of many tools. You are going to need an impact driver to remove the screws on the crankshaft cover. This is so you can turn the motor over with a 19mm wrench.

Also as a reminder...disconnect the battery....we had a few here that have had an oops with the battery still connected.

Make sure you find and read the write up on compression testing, you have to disconnect the tci unit or risk having to replace it after the test...

Colortuning is the final adjustment of the air/fuel mixture screws, but there is a write up by Rick on an old school way of doing that by ear...I'll see if I can find the link.....

And no need to worrying about offending, Just trying to be helpful without sounding like a butthead..

 

Ok. So I start on cylinder one intake valve. Lobe points away from bucket. Move to intake 2, rotate 180 and lobe should be pointing away from bucket, and so on. Then over to the exhaust. Point lobe away from bucket. Move to exhaust 2, rotate 180 and lobe will be pointing away, and so on. This sound correct?

I did break the rack and I did take pics. Actually took a video as well just to be safe. However, I have no idea where the pics are and I deleted the vid because it was on my phone and taking a lot of space. I got rid of them after I re-assembled the rack of course.

I have them off the bike but still together so I can take a pic and post it. Maybe I missed something. But like I said, this bike ran perfect last season. Synced fine after I rebuilt them. This time I took them off and cleaned them because of some bad gas. Blew out the other passages gently with compressed air, making sure not to blow out any seals. Put them back on and she started right up. Then tried the sync and here I am. I have no clue what would be causing them to be so out of wack if the linkage is correct. Maybe the pilot screws? I have new o rings for those but didn't put them in yet. Maybe that would help? I'm just shooting in the dark here. Either way. I'll get a pic up here.

 

That's funny you mentioned that shim pool. I was sitting here today thinking, "hey, I wonder if there's some sort of shim swapping thread". Ha. I should have known. I'll check it out.

So it's not the shims that wear huh? It's the cam lobes? I mean if you can swap shims and they stay the same size.... Interesting.

You guys don't sound like buttheads. You're all very helpful. If anyone is the butthead it's me for trying to rush. I'm really just trying to get this done with the least expense but, I realize there's no skimping on certain things or it's all in vein. I thank you guys for your patience. That's something I lack sometimes, hence trying to rush through this whole ordeal. I just hate seeing her sit in the garage. Not to mention the ol ball and chain "why do you have that, it's just taking up space, it doesn't even work, you don't even ride it". Blah blah blah. Shoulda married a biker chick.

 

Keep asking questions and heeding answers and there will be no butts about it!
No the shims do not wear nor do the cams, the valve itself seats differently (someone smarter than myself can provide better detail). However you may not wish to fill your head with more stuff. . . .

Wives are interesting, I spent pretty much all day yesterday working on my XJ. Even thought it wasn't on SWMBO's "Honey Do" list, she didn't complain. Although I did notice she was getting a collection of empty beer bottles by her!

 

Although my head is full of a lot of great information, I think I understand. Carbon build up, Valve face wear and tear, Valve seat, stem, maybe even spring tension, etc...

Don't worry, my quest for knowledge, or lack there of will force the questions to keep coming.

I spent a good part of yesterday doing the same. After I spent all day Saturday driving her around to shop for Halloween costumes and mowed the lawn she really couldn't complain. Plus, I think she sensed my frustration so she pretty much kept her distance. Heh heh.

 

The primary cause of changes in the valve clearance, especially early in life (most xjs were put away early in life mileage-wise) is the valve clearance (what you measure) shrinking from the valve pounding into the seat. It's not wear, more like work hardening, the further they pound into the valve seat, the closer the shim gets to the cam. At some point, they are held open and the interface burns. You don't want to get to this point. Valve clearances are supposed to be checked at 2500 miles, and every 5000 miles after that. They settle down beyond 20000 miles or so.

My Turbo Seca had less than 7000 miles on it when I got it. Checked the valve clearances and 7 shims needed changing (some by even two sizes!).

Later in life, the primary wear will come from the surfaces, like the cams, wearing. How many miles are on that engine?

Valve springs have nothing to do with valve clearance measurement, you need to disassemble the head to measure them. If you build up carbon on the valve seat, you lose compression. Adjusting the clearances wouldn't fix this.

 

Simply put, the valves pound themselves deeper into the head, causing the clearances to tighten.

As the clearances tighten, the valve spends less and less time on it's seat and more time open; eventually being open SO long when it should be closed as to affect compression.

An XJ with ignored valves will run fine right up until the day it won't anymore.

 

Ok. Float question. Before I do the wet adjustment I should do a dry one correct? Now the picture I've attached say to turn the carbs upside down. Now my carbs, when on the bike, the float bowl faces towards the back of the bike so if I place them upside down, the floats will kinda just hang there. It also shows the carb on an angle, not level so I'm all sorts of confused. I though the carbs had to be level, float bowl up and float just resting on the needle valve wthout the spring depressed. If I do that though, the floats don't seem to go down much when I press on them to depress the valve spring. I set them at 7.2mm. The specs say 6.2 - 8.2 (which that pic doesen't show, might be eur and Canada models) so I figured I'd start in the middle. BTW I have the Mukini BD28's if I'm not mistaken. How the heck am I supposed to adjust these things?

Also, Fitz, I did look at that PDF ya gave me the link to but I'm still a bit unsure how to do it correctly.

 

copied from xj4ever...

In order to achieve the proper fuel level.....as measured by the "clear tube method" outlined in the service manuals......there obviously will be some particular "float height" that will achieve that FUEL LEVEL. But that actual float height can vary between various carbs due to a number of factors; for example, in the case of the Hitachi carbs, it also depends on which set of float valves and needles were originally installed by Hitachi (we've seen three different types in original carbs) AND which replacement style of needles and seats that you purchased. The factory specified "float height" is for an original carb, using the original float needle seats and valves, which may no longer be available for your bike.



The float height determines what the fuel level within the bowl will be (since the float height determines when the float valve needle assembly "cuts off" fuel flow from the gas tank into the carb bowl), and thus an adjustment to the float height is how you adjust the fuel level. The float height is adjusted by very small amounts of bending the float TANG ARM on the float supporting structure. This tang is the central metal "arm" that contacts and supports----via the little float needle clip - hook (on most models)----the float needle itself. You would bend this tang down (away from the needle) to raise the float height (and thus raise the fuel level in the bowl), or you would bend this tang upward (towards the needle) to lower float height (and this will lower the fuel level in the bowl).


Please note that although you typically are messing around with the float height and adjusting that tang WHILE THE CARBS ARE UPSIDE DOWN----so you can easily access the floats----the descriptive actions such as "downward" and "upward" that you may read about in various manuals are describing such directional movements in relation to the normal orientation of the carbs as on the bike! THIS CAN BE INCREDIBLY CONFUSING WHEN YOU FIRST START PERFORMING THIS ADJUSTMENT PROCESS!!!


Also note that the fuel level check (with the sight tube gauge) must be done with the carbs oriented in the same manner as if they were installed on the bike, meaning perfectly level from side-to-side (you'll want to use a bubble-glass level to make sure they are perfectly level) and completely "vertical". NOTE: the "vertical" orientation confuses some people, as the carbs, when installed on the bike, are actually tilted a bit forward from true vertical in the normal riding position. However, when checking the fuel level with the sight tube gauge, the carbs should be in both a horizontally and vertically level orientation.


Here are some other useful hints, culled from the factory service manual, regarding how to prepare yourself for the correct check of the float height measurement:

- Hold the carb in an upside down position.
- Incline the carb at 60-70-degrees so that the end of the float valve does not hang down as a result of the float weight.
- Measure the distance from the mating surface of the chamber without the gasket in place, to the top of the float.
- NOTE: the float should be just resting on, but not depressing, the spring loaded inlet needle.


Well, okay! Now, although you may not have noticed it immediately, there is a very important and very cryptic passage in the above set of instructions, which is this:

"Measure the distance from the mating surface of the chamber without the gasket in place, to the top of the float."


The "mating surface" is, of course, the bottom of the carb body (where the float bowl gasket would be located) but without the gasket in place.......check. But the next part......the "to the top of the float" bit......well, that's a bit more mysterious, because:

a) of course, as it with the "direction warning" issued earlier, the "top of" the floats, when viewed with the carbs being upside down in your hands (which is the only way to perform such measurements), is actually the physical bottom of the floats!

Told you this would get interesting.......

But that little detail aside, now we have to explore the more challenging part of that statement, which is "what and where, exactly, is the "top" of this bottom of the float?"

This simple question is, unfortunately:

a) not so easy to answer, and.....

b)varies by which carb model you are holding, upside down, in your hands and trying to measure..........



For some models, the information as to exactly WHERE to perform this measurement at the float is either not known, or incredibly confusing.....and the factory service manuals are not much of a help in this regard, what with their tiny, grainy images. It seems as though Yamaha wanted people to focus on the fuel level setting (of course, as that is the end result you're actually shooting for), and figured it wasn't worth the trouble or effort to go over the float-height-measurement procedures necessary to achieve that--------rather, they tell you what fuel level measurement to acquire, and then tell you to just "bend that tang arm" and re-measure the fuel level and just keep going back-and-forth until you get it right! And then do that messy, smelly, spill-gas-all-over-yourself with this trial-and-error procedure three more times.........



Three Blind Carbs: See How It's Done:

Because of all the considerations mentioned previously, and due to the importance of getting this job done once, and done correctly, the procedure that we suggest you follow is to work on achieving the proper FUEL LEVEL in any one carb.......so, install the needle and seat, install the float, fill the bowl with fuel, and measure the fuel level (although the factory gives a rather wide range of acceptable fuel level limits, such as 3mm +/- 1mm----in other words, anywhere from 2mm to 4mm----we feel that you should always strive to get that fuel level right in the center of the range (in the above example, right at 3mm).

You'll do this by very slight bending of that central float tang arm (the one that the needle clip fits over) until you get the measured fuel level (drain and measure a couple of times, to be sure!) that it's correct.


Now, since you know that this one carb fuel level is correct, and if you're using the same float seats and needles in all the other carbs, then simply measure the "float height" of this now known good carb.....and, you can "measure" that height in any way and at any point that you desire, preferably whatever measurement is the most consistent to perform and the easiest to see.......and then that becomes your "float height" for all of the other carbs, too. Just adjust the other float tang arms to achieve that same unique "float height", and you're done!

BUT, I would still fill and measure each individual carb and check the fuel level, just to be sure, before you install them on the bike!


The above may seem like a more time-consuming and "tedious" way of doing things, but it is the only way that we know of to make CERTAIN that your fuel levels are correct........rather than having a "correct" float height.......and as we stated earlier, it is the fuel level that is the end result that you're seeking, not any particular float height (except for the necessary float height needed to get to that proper fuel level, of course!).


The proper FUEL LEVEL is a vastly over-looked, but vitally important part of having your carbs perform properly, as improper fuel levels WILL result in either lean or rich fuel mixtures, and will most likely tempt you to try to "compensate" for such a situation by other, NON-NECESSARY and perhaps COUNTER-PRODUCTIVE changes in other circuits or carb settings, which may affect and degrade other areas of the engine performance. IT IS ALWAYS BEST TO ADDRESS AND SOLVE THE "ROOT" PROBLEMS (or, to put it another way, to FOLLOW PROPER PROCEDURES AND ACHIEVE PROPER SETTINGS) in all of the basic areas.

This method will allow you to actually save time, money, effort, and achieve more accurate, consistent, and reliable results!



Fuel Level Cheat Sheet:


Hitachi all HSC32 series models:

-Fuel level measured via the clear-tube gauge: 3mm +/- 1mm (.12 +/- .04 inches)


Hitachi HSC33 series (XJ700 models):

-Fuel level measured via the clear-tube gauge: 1.0mm +/- 1mm (.039" +/- .039")


Hitachi HSC33 series (XJ750E-II model):

-Fuel level measured via the clear-tube gauge: 5.0mm +/- 1mm (.197" +/- .039")


Hitachi HSC33 series (XJ750RL models):

-Fuel level measured via the clear-tube gauge: 1.0mm +/- 1mm (.039" +/- .039")


Mikuni BS28 (all 550 except 550L):

-Fuel level measured via the clear-tube gauge: 2mm +/- 1mm (.08 +/- .039 inches)


Mikuni BS32 (all 550L):

-Fuel level measured via the clear-tube gauge: 3mm +/- 1mm (.12 +/- .04 inches)


Mikuni BS30 (all 650 Turbo):

-Fuel level measured via the clear-tube gauge: 2mm +/- 1mm (.08 +/- .04 inches)


Mikuni BS33 (all 700-X and 750-X):

-Fuel level measured via the clear-tube gauge: 3mm +/- 1mm (.12 +/- .04 inches)


Mikuni BS35 (all 900RK):

-Fuel level measured via the clear-tube gauge: 5mm +/- 1mm (.20 +/- .04 inches)


Mikuni BS36 (all 900F, FN, N, etc):

-Fuel level measured via the clear-tube gauge: 5mm +/- 1mm (.20 +/- .04 inches)


Mikuni BS34 (all 1100):
-Fuel level measured via the clear-tube gauge: 3mm +/- 1mm (.12 +/- .04 inches)



Okay, the fuel level measurement is done via the clear-tube gauge method, and this tube should be positioned along the SIDE of the carb body being measured (not along the front or the back of the carb body), and along the centerline of the carb body, basically in-line to where the main fuel jet would be located. The fuel level is most critical to the performance of the main fuel jet, so that is where the fuel level in the bowl should be measured at.

The actual fuel level measurement (which reads something like "3mm +/- 1mm") refers to the level that the fuel in the tube is located below the bottom edge of the carb body where the carb bowl is bolted to the carb body. NOTE: as fluids like to do, the "top" of the fluid level in the tube will not form a perfectly straight "top" in the tube......instead, it will be somewhat "u-shaped". The proper measuring point is the lowest level of the fluid in the tube.



Whew! I told this is a tedious process; luckily, once you get the float heights (and thus the fuel levels) set correctly, it doesn't change very much over time, so you don't have to go through this procedure very often, or maybe even ever again!

Unless...........something occurs that physically bends that float tang arm, and thus changes the float height and thus the fuel level in the bowl. Besides "time" and "metal fatigue", the main culprit that can bend this tang arm is excessive pressure on this arm, typically caused by a stuck, seized, or jammed float needle, which holds the needle open and lets fuel keep coming into the bowl....thus the fuel level rises, pushing the float upwards, and the tang arm exerts excess pressure against the float needle, and ends up bending the tang arm due to such excess pressure.

Float needles can become stuck due to defects in the needle itself, the cylinder bore of the needle seat, or perhaps a piece of gunk from your fuel tank made it through the filters and gets lodged into the needle seat, seizing the needle open or preventing the needle from ever closing fully against the seat. Then fuel keeps flowing into the bowl, the float level rises, excess force is applied to the tang arm, etc. A worn needle tip.....which may also prevent full closure of the seat opening.....can also cause high fuel levels.

Also, please note that on models on which the float needle has a spring-loaded "tip", that this tip should NOT depressed when setting the floats, nor should it be seized open nor closed. That needle tip is a "shock absorber" and does not and should not be depressed----at all----when setting the float heights. If that spring-loaded tip becomes seized shut, then the floats will have to be set very "high" before they ever rise far enough to exert enough pressure on the collapsed tip to force the needle closed, and thus will cause bowl flooding.


So: if your carbs flood, then the tang arm can bend, and even if you solve the flooding problem, you may find that after such an event you may have a continual fuel level problem.

Moral of the stories: check your fuel levels periodically (you can do this with the carbs still on the bike) and adjust them into specification if they are not!



Okay, if you've read all of the above and are not fully confused, well, it means that you just haven't been paying enough attention..........

 

I actually did read all of that in the church carb thread before I posted that last post. And yes, I am totally confused. I thought the dry method was to be done first while the carbs were off the bike. Then, when on the bike, the wet method. My confusion is exactly what position are they supposed to be in when I do the dry measurement? Level with the float bowls on top, at an angle as if they were on the bike, upside down? I don't have much hair. Please help me save what's left. Is it like the pic I attached? Level?

 

I dry set and wet set the carbs off the bike.....You can easily check the fuel levels on the bike, but setting the floats, they need to be off the bike in my opinion.

Taking the dry measurement you turn the entire rack so the float tang just touches the float valve without depressing it and the floats are hanging.
So it will be upside down and tilted.

Really instead of all the measuring and stuff trying to do a dry set I found it easier to "wet set" the #1 carb off the bike, with the carb rack on a pvc homemade carb holder. Make sure the carb hat is level front to back and side to side. Once I had it within spec, then I removed all the bowls, and by setting the other 3 floats to align with # 1 using the dry set method. If your holding the rack correctly, you will look down the row of floats and if the are lined up exactly with #1 you should be real close.

Reinstall the bowls and then replace the carbs on the holder and check the fuel levels to be within spec. If not, remove the bowl, and adjust the float tang. It does not take much to change the fuel level so don't try to move the tang much at all, almost just implied pressure.

Don't settle with the first wet reading from any carb..Drain and redo at least 3 times to take a final reading before adjusting.

Once you get your hands on it it will make more sense....there is always enough help around here to keep you from a total fupa.

 

Ok. So that pic I just attached on my last post is wrong? They should be on a slight tilt?

As far as the wet set goes, and i may sound like a jackass but how do I get fuel in the bowls while they're off the bike?

Unrelated question. Is there an app I can use on my phone to access this forum. I have tapatalk but I can't find this forum.

 

Need Fitz to chime in on the angle of the carbs. My bike has Hitachis. If the float is hanging and the tang is not touching the float valve, your close, now tilt the carbs until the float tangs just touch the float valve without pressing on them at all. That would be the angle....

I use a old lawnmower gas tank, shut off valve, and a length of clear tubing as a fuel line. Not a bad idea to have a fuel filter in there also.
As long as the supplemental tank is above the carbs, connect the fuel line to the carb fuel inlet and it will pour through and fill the bowls. Have a clean measuring cup to save what you drain back out of the bowls as you adjust the floats to recycle back into the supplemental tank. You can use the cheap clear tubing from home depot for the fuel line.

oh, btw...wet setting the floats are a major PITA...I think everybody will agree that you will have to exercise an extreme amount of patience and you should wait until your done before celebrating with the beer!! or whatever...lol..

I have been known to just walk away and do something else and then go back to it later. Sometimes it feels like your trying to hit a moving target, but once everything is in spec and sync'ed, your bike will run so much better...

hang in there..

 

Ok gentlemen. I checked my valves this evening. Well, just the intakes for now. I need your help deciphering this stuff. Basically my confusion is the measured clearance on the chart in the manual and converting it to the measurement I got with my feeler gauge. So here we go.

Cylinder 1 Intake
Measured clearance with the feeler gauge was .005 in which is .127mm.
The shim was a 278

now on the chart the clearances are stated in a different format which I probably just have to convert some how.
More like zero point something (0.00, 0.05, etc... or one point something (1.01, 1.05, etc...)

I don't even see a .005 or .127 on the chart. Any idea what I'm doing wrong or how to convert these numbers?

Actually, now that I'm looking at the chart, cyl 1 and 2 are in spec. Cyl 1 measured .005 and cyl 2 was .006. The acceptable range is .004 - .006. These are in inches of course.

Cyl 3 is .003in or .076mm
Shim is 280

Cyl 4 is .007in or .178mm
Shim is 278

Again, the chart is confusing. I don't know if the measured clearance numbers are in mm or inches. See the attached pic.

 

The chart is metric.
Gaps should be read with metric feeler gauges.
Use your cylinder 3 for an example:
Find your measured clearance in the left hand column. (.076mm) which is in the 0.06 ~ 0.10 range.
Your installed shim you cross reference on the top row. (280 = 2.80mm)
Now find where those two numbers intersect and it tells you what shim to put in to be inspec. ( you need a 275 to put #3 in spec).

You should really check what shim size is where in both intake and exhaust. Write them down (someone here had a cool excel spreadsheet) and figure out what sizes you need to bring things in spec. If the valve gods are smiling upon you; you can do the shim shuffle and swap things around and may only need to acquire 2 or 3 'new' (or shim pool) ones.

 

How did you calculate the range .06 - .10 for .076mm? That's where it threw me off. I thought my feeler gauge was metric because it has millimeters.

 

You read .003" which is .0762mm.
Rounded to 2 decimal places is .08mm.
( remember .01mm = .0004" that's truly splitting hairs kind of tiny).

Soooo, using .08 as our reference . . . .
The range is .06 ~ .10 . . . .
.06 .07 .08 .09 .10

 

might download this...it helped me

http://www.xjbikes.com/forums/index.php?threads/shim-calculator-excel.46030/

 

Thank you both. Math was never one off my strong suits. I actually asked my 12 year old daughter for help converting these decimal numbers. She did this stuff a few years back in school. Makes me feel like a dumb old man. I might just go buy a metric feeler gauge. Couldn't hurt to have one of those. That's one tool I'll probably use more than once and they're only about $6.

 

Good grief. Called o'riley, AutoZone and advanced auto parts and none of them have a friggin metric feeler gauge. What the heck?

 

You get fuel in the carbs when they're off the bike by rigging up an external fuel source.

I've usually "borrowed" the fuel tank off my kid's minibike and hung it from a garage rafter, but he sold the thing.

There are many ways to accomplish the task. Be creative.

 

Get on Amazon and find yourself a K-D Tools pn 2274. Widely available even after K-D got sucked up by Gearwrench.

(Most auto parts stores have/had a "K-D" rack, and a lot still do; and most of the snoids that work there have no idea what's hanging on it. You'd have to go look.)