I don't understand carb syncing..

All I have is a single vacuum gauge and I've been trying to get these carbs synced for about an hour now, I was following a guide on here that says get a base reading for 3, match 2 to 1, match 4 to 3, then 2 to 3...

But how the hell can I match anything to 3 when three is reading like 30 on the gauge and everything else is reading 12-15? I can sync all the other carbs but 3 is reading super high, whenever I try to sync the other carbs to it the bike either refuses to start or idles VERY poorly and dies quick..

I need a guide with a single vacuum gauge to get my carbs synced that isn't from 2006.. Starting from the very beginning, where to set my main idle adjustment screw, and then how to sync to port 3 (I'm assuming) when all my other ports are reading super low compared to it...

 

If it were me, I would put that gauge away. Do an internet search for carb synchronizing and you will find a ton of homemade sync tools that can be made very quickly and cheaply. Sync all four at once.

 

3 is synced by the throttle stop screw aka idle adjustment screw between carbs 2 and 3 at rear of carbs.

set idle to 1050 rpm. when you sync 1 to 2 readjust idle. then when you sync 4 to 3 readjust idle.
this should leave you with 2 sets of carbs that are synced ,
then sync carb 2 to 3 reset Idle.

you have to recheck the vacuum on each carb as you sync. by that I mean if 2 is at 12 and you adjust 1 to 12 then check 2 again.

if you get a fishtank air valve with 4 ports you can hook up all the hoses and just open and close the valves you need to adjust for the sync.

did you bench sync the carbs to start?

sync 1 to 2 then sync 4 to 3 then 2 to 3.
it is easier if you have 2 vacuum guages.

there is a old thread somewhere where someone used 1 guage and a newer one with the fish tank valve setup

 

Well I had hogfiddles helping me over the phone, giving me some advice. I got 1/2 synced together, then 3/4 synced together, but when trying to sync 2/3 now the bike starts taking off climbing RPM with the idle screw at the bottom already turned all the way out.

He explained to me that when you adjust one carb you're actually adjusting both, I didn't realized when I was adjusting 4 to match 3, it was actually making 3 go lower as 4 went higher.

 

Post
Single vacuum synchronizer with good enough results..

Old School Method of One Vacuum Gauge Carb Sync

 

I have pilot air mixture screws about 3 1/4 turns out, if not then I get lean popping and the bike sputters HARD at low rpm, the idle screw is all the way out with 1/2 synced, 3/4 synced. The problem is that when I try to adjust 2/3 now the bike starts running away in rpm. Should I try messing with my pilot air screws again? When I tried earlier while adjusting the carb sync is was making the bike leanpop really bad.

 

stick with the program. when you adjust 2/3 your really doing the pair (1/2) to the pair (3/4).
your idle is going up because (3/4) can't go closed more{idle screw} so (1/2) is opening, the idle goes up.
sync. idle. repeat that 5 times and see what you got

 

So what you are saying is that my 1/2 and 3/4 respectively are fine, but while adjusting 2/3 it is causing 1/2 to open up (push itself up because 3/4 is deadstop) because it cannot adjust 3/4 any further in the direction it's trying to?

So what it sounds like I need to do is adjust my idle screw in to get the bike idling off of it, even if it is a high idle rpm, and adjust from there because that will give 3/4 room to adjust since their not deadstopped anymore? Also I don't have the gauge cluster on at the moment because I was in the middle of taking the Seca cluster off the PO had on it and have been working with hogfiddles on trading for a functional Maxim unit.

Hogfiddles has been a HUGE help with all of this so far, without him I wouldn't of even gotten 1/2 and 3/4 synced together, he explained to me that when you adjust one down it's really adjusting the other up at the same time, and that when adjusting 2/3 it should be keeping the 1/2 and 3/4 adjustments moving together up or down.

So the TLDR of this and the bullets I need answered...

1. Adjusting pilot mixtures won't really help in this situation?

2. Could it still be a vacuum leak somewhere? I sprayed the boots on both sides of the carbs with starter fluid with no real noticible difference in the rpm.

3. Hogfiddles recommends taking the carbs back off once more and doing a bench sync since I haven't done that previously, but the carbs are already so close to being synced, is that even necessary?

4. Should I remove the carbs and the rubber boots on both sides to give them a healthy layer of RTV Black to attempt to seal any micro cracks that might be there? There are slim small stress cracks in the rubber along the sides of some of the boots but when sprayed with starter fluid they don't fluctuate the rpm at all.

5. The bike will idle fine (when it does) for a bit then suddenly act like it dropped a cylinder for a second or two before regaining itself and going back to idling, does this sound related to my problem here?

6. Next steps to take: Adjust the idle screw to get the engine idle rpm slightly high but consistent, then take readings of 2/3, leaving my SINGLE vacuum gauge on 2 while performing an adjustment to the 2/3 sync. Adjust the main idle as necessary to make idle consistent again, adjust sync again, adjust main idle AGAIN, THEN FINALLY check all carbs vacuums to ensure their all atleast relatively in the same ballpark of 1-2 ticks on my vacuum gauge? Correct?

 

Get rid of the single gauge. Get the Morgan carbtune. What I was telling you was based on using a 4 stick gauge not a single. You’ll never see them balance with one. With the four, you can SEE all four.... that’s what I was describing to you.

Yes, you balance 3 with 4. Yes you balance 1 with 2. The you balance the 1/2 combo with the 3/4 combo.

But you should not have the idle screw so far out that it’s not doing anything. That indicates a butterfly is either so far closed that it’s holding others open like I told you, or you have a vacuum leak. You eliminated that from the list. If your butterflies are so far out of whack, you may need to pull the rack and get a bench sync so they’re close enough to try again. I’ve been able to straighten them out while doing a sync, but it can be a challenge. Typically it should take just a few minutes to do your sync.

if worse comes to worst, put the bike on a trailer and come up.

call me again tomorrow .....
Dfox

 

Finally got my carb tune pro, and colortune from chacal XJ look out, it’s going to be a beautiful weekend and I plan to ride ya!!!!!

 

Considering I'm already semi-over budget for this bike and reluctant to spend more for it, I'm going to get two gauges and get a "good enough" tune/sync on the carbs, then ride it up to Hog and he will help me more with it. He's been such a great help, I see you are in NY same as him, if you ever need help shoot him a message Jonathon, he's an amazing guy.

 

@Maxwell Partridge
1- not really, not yet
2-it could be but it doesn't sound like that's the problem
3- you can always save that as a last resort
4- you don't want to pull the manifolds off of the engine side unless you have good reason, bolts can snap and things get ugly fast. save that for later once you know it's a problem
5- that could be a mixture problem but get the sync sorted out first
6- make one of these and life will be easier https://www.instructables.com/id/DIY-DualTriple-or-Quad-Carburetor-Sync-Tool/

 

Are you referring to Hogfiddles? If so of course he is. I talk to him frequently. He is about 2 hours down the road from me.

 

I got another gauge on the way so I'll have two in total to be able to adjust my carbs, it should be a TON easier than trying to dance around the carb ports with just one. Thanks for the instructable though, as a last resort I will use that instead of spending 120 bucks on what HogFiddles recommended to me. I'm not saying what he said to get is a bad tool to have, but it's out of my price range already since my limit for this bike was around 2k at the most and I'm getting near $1,600 already without even getting into cosmetic things I want yet.

Bike - 400
Title/Registration - 260
Gas to transport it to PA from NY - 80
Initial fluid replacement for oil and final drive + Misc things like Seafoam/Marvel Mystery Oil - 85ish
Two carb gauges - 33
Valve Tools - 23
Feeler Gauge - 9
Aftermarket clutch/brake levers x2 (first clutch lever broke on accidental drop) - 55
Carb Rebuild Kit - 53
Starter (not clutch) rebuild - 17
Clutch Cable - 15
Shims from hogfiddle (pending 32 back) - 45
Payment to Chacal for clutch rebuild kit, valve cover gasket, and a single shim hog didnt have - 252
Gas used riding/diagnosing - 25ish
Insurance yearly - 25
Replacement headlight housing - 20
Oil filters x3 - 23
Torque Wrench set - 58
New handle grips - 12 (Technically I purchased new ones for my other bike and re-used the ones from that on the Yamaha, so not counting this in the total)
New O-Ring for oil filter housing plus bolts for carbs and engine side cover -stainless steel- (some got stripped, the + Philips on the left side cover that says Yamaha) - around 60
Something I might be missing/forgetting to list - 50

Total - $1,568

I'm not saying the bike is a bad bike, or that it is not worth fixing back up and getting in running condition again, but honestly the more money I keep having to put into random tools that I'll use once and prolly never touch again just gives me a really disheartened feeling in my chest. I like the bike, A LOT, I've always loved these older classics, but it's just getting to be abit more of a financial burden than I originally assumed. I'm not saying I'm not willing to spend money to fix it, but if I can do something using 2 gauges (for example) that cost me 33 bucks instead of spending 120+tax on a "pro" 4 carb sync tool I'll gladly go through abit more headache to get the same result.

My total is around 2k for the bike I want to be comfortable spending, and eventually I'm going to have to rip the engine and replace the one-way clutch rollers and stuff associated with that because it is giving me the horrid rocks in a can sound when turning over. It still initially grabs enough to get it started (when the bike is hot it's kinda a bitch but still eventually gets it started after a minute at most, pop-starting is always an option), I'm estimating that gaskets and the parts associated with that alone may be around 350 dollars to do that job. So that's just another reason I'm trying to be a cheap bastard about the stuff I know I can be on...

 

I fully respect everyone that has helped me thus far and all the information/resources that they have provided to me, I do not mean to be disrespectful to anyone saying what I need to get, but I simply cannot afford the same luxuries in tool choice as they can.. Especially with this virus going around f***ing the economy..

 

And that’s why I got the Morgan carbtune pro as soon as I could. I use it every year, for mine, for carb clinics, for local help..... and it usually takes just a few minutes to dial in a bike. With one gauge, I would expect it to be a lot longer and a lot more frustrating. I can see all 4 cyl at the same time, and jump from screw to screw very easily.

 

one word of advice, burn that list and never think about it again

 

A lot of things on your list of expenses don't really belong on that. I'm surprised you don't have a few beers listed on there too haha. Tools don't belong on there because you will always find a place to use them again torque wrenches on just for motorcycles. 3 oil filters that's two to three years worth of riding. gas for test riding the vehicle nope. Cost for going to pick up the vehicle didn't you enjoy the ride.


You could have built the homemade sink tool for less than $10. Insurance and registration nah they don't belong in that list.

 

Gas doesn’t count either

 

If I kept a list of expenses of my hobbies, I would never do them.

"If you ride a motorcycle, you don't need a therapist"

 

It was just a list of all the expenses I've had to make since purchasing the bike, for the bike... I'm not saying things like tools wouldn't be needed for other things EVENTUALLY, but they were needed specifically for this bike to ensure the engine casing and clutch springs were torqued correctly. I also counted gas because it is gasoline that was used in the process of testing/adjusting the bike, no where near actually enjoyable riding in terms of cruising down the road without engine sputtering, stopping to adjust mixtures, ext....

You guys seem to be taking it the wrong way as in I'm trying to find every reason to complain about the cost of quality, I'm not... I simply said I'm trying to keep under 2k for a fully operational functioning bike that looks halfway decent with a good power footprint, I'm creeping closer and closer to the 2k mark, that is all....

 

No we’re not— we’re just having fun. Basically, we’re saying don’t keep track or you’ll get really discouraged. MOST of us have put more into our bikes than we’ll ever get out money-wise if we sell. But nothing can ever equal the fun/satisfaction/enjoyment price when it’s done.

I have absolutely no clue how much $ I have put into any bike I own. I don’t keep track other than how much I might have paid initially.

 

The great thing about fixing these Yamaha's is not only in doing the work yourself but the fact that once a bike is sorted it will give years more service with regular maintenance.

 

yup price of bike is only dollar amount listed in my journal for bikes.
parts and work is there but not the cost.

any used bike you get will require money to make it safe and reliable, just yearly maintance on your bike will quickly add up.
proper brakes to stop are $$ MC rebuild. caliper rebuild, pads, new shoes, brake lines. this is a must do item.
check year codes on tires, I hate having to buy tires but if out of spec new shoes for the bike.
one crash for safety related items failing will cost more that getting it right .

sometimes it takes longer to get bike ready for the road than you would like, but when its done your first ride makes it all worth it.

picked up a XJ900 it will be a while before it will be road ready may have to buy a new motor.
may have to sell a bike to finance this project, just can not bear the thought of selling a bike.
I may have to pick up a honda or HD to fix and sell. Just not an XJ.

 

Yup, and my 650rj is a good example.... bought it 7 yrs ago.....it’s STILL tying up my lift. But at least it’s almost done now

 

So here's an update... Got the carbs synced, they idle REAL NICE now, but I also found out in the process that I do actually have a vacuum leak, in my butterfly seals.... When trying to start the bike once I noticed some smoke coming out of the right side (outside) of carb four. "Huh, where the hell did that come from?" I spray starter fluid in the intake to make it backfire on purpose and then I saw it, smoke came right out of the butterfly seal... RIP... I sprayed starter fluid onto it and yep, it made the idle go down SLIGHTLY every time I sprayed it. I missed this before because the carbs were not synced so it was idling poorly to begin with, making the change in rpm pitch (which is subtle) hard to detect. How expensive is it going to be to replace all the carb butterfly seals, are they just o-rings or are they some proprietary kind of seal?

The leak is what I am assuming is what causes the bike to suddenly drop rpm every few seconds, the sudden influx of air the bike is not expecting is making the engine stumble over itself.

 

I just took one of the throttle shaft sides off of my spare carb to see what I'm dealing with, and it looks like a square-type o-ring, I assume that a simply o-ring from a hardware store will not suffice here? Also, is there a way to get at it without REMOVING the throttle shaft? of am I going to have to do that? I just don't want to risk ruining the small Philips attaching the throttle plate.

 

No (besides the outer seal on each of the two outer carbs).

Yes.

With the correct size JIS screwdriver, you won't, but even if you do, replacements are available.

 

Chacal sells the throttle shaft seals both oem and aftermarket.

you can use regular style orings if you wish to go that route.