New to forum and carb questions

Hello everyone! Brand new to the forum and the XJ line of bikes. I bought a used 81 XJ 650 a few weeks ago and I have been going through the entire bike. I have yet to hear the bike run because I want to get everything sorted out first. It was in pretty bad shape and so many things were backwards or wrong with it from PO. I am slowly working it out. I have cleaned and separated the carbs, new throttle shaft seals ( thanks x4forever!), jets etc. The problem I am having is the carbs were originally attached to a 750. The jets were for a 750 so obviously larger sizes. Ive already replaced the main and secondary fuel jets and needles etc back to stock recommendations for the 650. The pilot air and secondary are 225 and 80 that are in there now. My concern is how well it run with the larger jets. Could I just color tune it and move on? Are those air jets only used for idle mixture? All of the other jets , compensater and other fuel jets match with the 650. Thank you so much all and I look forward to a long membership!

 

The larger air jets will lead to a hanging/runaway idle. and a lean mixture at higher RPM.
There is one air jet for the pilot, and one for the main.

Be aware that the diagrams in all of the service manuals hae the positions of those jets mislabeled.
The photo below is correct.

 

Thanks for the info kmoe! Ok, ill track down the 195 and 50 air jets I had no idea they had that much influence. That would drive me crazy.

 

carb jet specs
http://xjbikes.wikidot.com/carb-specs

do not know if this will be an issue do not quite understand this part on carbs yet
81 xj650
Main jet NEEDLE ID: #Y-12

81 to 83 XJ750
Main jet NEEDLE ID: #Y-13

 

It would be an issue, but he already changed them. Different jet needles change the rate at which the fuel to air ratio is adjusted as the slides lift.

 

Thanks all. I will be sourcing air jets through xj4ever. I have a new problem i just discovered. This bike was Frankensteined in a bad way. Originally titled as a 750 82 xj the po installed a 650 motor instead of a 750. Additionally after research its not a YICS and is an 81 maxim engine. The 750 tci is in place so i have no idea if that will work with a non yics engine. Any experience with a 750 yics tci on a 650 non yics? Im trying to source an 4h7-10 tci but having issues finding one. Thanks everyone for help!

 

the nonyics has differert timing in its tci but yics 650 and 750 are the same

did you id the motor as seca or maxim 650?


you are looking for green label tci.

there are also black lable tci for the 650 I think it was used on the midnight 650 do not know if it matters
I have a black label tci from a 650 midnight maxim

I was going to buy a midnight motor but got out bid at last moment and had already purchased a black label tci from another midnight.
side note they will all start and run the 650 or 750 motor

there is a thread/discussion on black tci someplace.

 

It seems to be a maxim engine from the serial number but I am not 100% sure. The number plate on the engine is 4H7-004330. I managed to find one on ebay ( black label) so hopefully that is the correct box. I can only imagine how terrible this bike ran before i got it.

 

650's:

1980-81 XJ650 Maxim USA: 4H7

I would have given you the full monte but the link for that is broken
http://www.dissingermoto.com

 

Thanks XJ for confirming. Things are slowly getting there after sourcing parts. Just about done with carbs they were a mess.

 

Actually, the 650 non-yics and the 650 yics/750 TCI's use the same advance timing, the only difference between the 2 boxes is the inclusion of a grounding pin for the sidestand safety circuit on the '82-up (650 yics/750 all) models. The non-yics box is the 4H7-10 black label version, and the yics version is the 5G2-10 red labelled box.

The green label box (5V2-10) is for the XJ650RJ Seca (non-yics) versions, and its timing is slightly different. The 650RJC Canadian Seca models got a yics engine, and thus uses the 5G2 box.

The 5G2 (yics) box will work just fine on the earlier XJ650 non-yics engines...…….it has an extra grounding pin which isn't going to be hooked up to anything. Note that the reverse situation is not true.....using the black-label 4H7 (non-yics) box on a 650 yics/750 engine will allow the engine to perform the same (since they have the same advance curves), but you'll lose the sidestand safety feature (which is something you definitely want to have!).

And just to clarify: the difference between the black-label 4H7-10 and the red label 5G2-10 tci boxes is not due to any advance/timing differences, it is only due to the use of the grounding pin on the 5G2 boxes...…...the 1980-81 XJ650 Maxim/Midnight Maxim models did not use a sidestand switch/relay/safety feature, and thus no grounding pin (to disable the TCI under certain conditions, i.e. "the sidestand is down" safety feature) on that earlier 4H7-10 tci box.

 

thanks for clearing that up

 

Thanks for the info chacal! I ended up ordering one from eBay ( black box ) so apparently I didn't need it after all. Ill try to resell it, The red label is on the bike now (5G2) I will leave it in place if the advance is the same. Its not been fun reworking things as I mentioned the PO put a 650 engine when originally it has a 750 in it. I have had to swap jets, buy related parts etc. Excited to hear it run for the first time and correctly. I am also wondering if the tach will work still since it had the Atari cluster in it. The 650 motor has the mechanical tach output on the front so I am not sure if the tach will still work. Apparently its connected to the coil so I would think it would. The original 750 main wiring harness is still on the bike.

 

The tach will work so long as it's connected (and in working order).
Chacal sells a blanking plug for the mechanical tachometer port if there's not one there already.

 

Thanks everyone for your help. I got the carbs completely rebuilt, throttle shafts fuel o rings cleaning everything. Put them on bike and sync and color tuned. Idled decent but I had to play around with the control knob to get a steady idle. When I rev it up it hangs and takes a bit to come back to idle. I also adjusted the valves. The bike falls flat on its face at 5k rpm and sputters. It seems like it looses power. One thing to note is that there is a small fuel filter attached to the output of the petcock. The bike also has a manual petcock installed. I checked the boots with starter fluid and didnt find leaks. Could this be a bad coil issue? I am also having an issue on restart after its ran for 5 or 10 minutes. The starter turns over slowly and takes an extended crank to get it running again. Any help would be greatly appreciated thanks everyone.

 

Do you have an air box?

 

Yes, I had to buy one because it originally had pods. Put on the correct 650 air box and boots are good all the way around. I had a few things out of sort so its gotten better. I am still having a slow to return idle. Spark plugs are perfect brown. Sync good, new spark plugs and caps. The slow to start after warm was due to a bad battery it wasnt charging. Put a new one in and its charging well and starts good when hot now. I also have some dyna coils on the way.

 

fuel filter or clogged vent in gas cap you need a sintered bronze filter

Your Gas Cap and You

 

Ok all I am still having issues with the bike. I still get a hanging idle and slow to return to idle. Also I cannot get the bike to rev past 5,000 rpm under load. Wide open throttle it doesn't budge past 5k and just sputtered. It will go to redline not under load. I rebuilt the carbs with all new seals including the throttle shaft seals. Carbs are colortuned and syncd. Just finished putting dyna coils and new spark plugs in. Inline filter is clean and flowing well. What else can I check? I do have the stock airbox and filter installed. Thanks

 

color tune and sync after shims done? if not re sync carbs and color tune.
did you wet set fuel levels of just set floats to 17mm I think?
do all exhaust pipes get hot and equally hot or do you have a colder pipe?

air jets in correct location? you can check this with carbs on bike.

idle must be adjusted after riding bike for 10 or 20 miles not in your drive way after a cold start.

 

Hmm that could be the problem. When I set float height I measured 3mm from the center of the float to the carb bowl surface on the carb. They are supposed to be 17mm? I have a float level gauge that's what I used. Seems like I did that wrong, they were already at the 3mm setting when I took of the bowls. Yes I made sure air jets were correct located. Pipes equally hot. I also synced and colortuned after reshim. I also had to "repair" the carb boots as they were pretty bad. I used shoe goo, and liquid tape. I sprayed around the boots and no increase in idle. I still wonder if this could also be the culprit. I am also concerned about the float level now !

 

You set the floats to the fuel height spec.
Here's the full procedure: Setting the fuel levels

 

Wow thanks k-moe I failed to do this one right! Thanks for this

 

So far they are out of spec! Gap was probably 20+ mm. Oh the joys I have had to fix from the PO.

 

Floats set to correct levels. Carbs reinstalled... problem still there. Hanging idle slow to return and hit a wall at 5500 rpm. If I stay in 2nd I can sometimes push it past 5500 to 8k or so but 3rd to 5th the bike stops dead at 5500 rpm. Any suggestions? Thanks everyone, this bike has been a chore to get right.

 

Have you got decent compression? If yes have you tried raising the needles to see if it helps? You could be getting too little (or far too much) fuel from the mains.

 

Long shot but are the needles ok? I discovered yesterday after a frustrating couple of weeks not being able to get past 60mph and 6k revs that cylinder 2 wasnt performing as well as the others.

I'd checked shim clearances, colortuned and vac synced as usual but the culprit was the needle. All floats set to 17.5mm as per instructions and wet set was in spec. The needle spring (the circled part in the pic) was too weak so wasnt giving the support to the float flange and was allowing too much fuel in.

Have you checked the spark plug colour to see if it's running rich / lean?

 

I will check that. When I had the carbs off the float needles looked ok visually so I put the orginal ones back in. They were the only thing I didnt replace during the rebuild because of that. I have 4 new ones ill swap in to see if that makes any change. Thanks, this may be it. Could this possibly be a TCI box issue?

 

Best way to troubleshoot a TCI is to try another one - do you still have the black label one you purchased earlier? A timing light can also be used to check for advance, although being precise is a bit difficult without some pretty decent equipment. And, just a stretch on an issue is the hodgepodge of parts you have. I don't know all the details, but I do know the reluctors are different on the 650 Seca engine. What I don't know is what might happen if a 650 Seca reluctor was combined with a red label TCI. I do know the converse of that, and that dwell time is considerably different when using a 750 Seca reluctor with a green label TCI as compared to the red label TCI. And to check - the 750 Seca (red label TCI) is 20.5mm, the 650 Seca is 17.75mm measured at the very end closest to the pick-up coils.

While you have the carbs off check the slides by lifting them and noting how they return. Improperly installed slides or holes in the diaphragm is going to cause a major loss in power and limit the revs if the slide is not lifting. With the caps off the slides should lift and clunk to the bottom of their stops. With the caps on they should be slower to return, which indicates and airtight seal is present. I found this video of a guy demonstrating a defective installation where the diaphragm was not properly installed in the groove. You can also run the bike with the air box boots off and verify the slides lift when the motor is revved.

 

Thanks for the info rooster. Yes I still have the black box (4h7) TCI. I will swap that back in but I seem to remember it still ran the same way, 5500 wide open. I did have an issue last week where the float was sticking closed on #1. I figured it out because the pipe was not hot on that cylinder. Ill check carbs again.

 

TCI swap to black box 4h7 did not change problem. I pulled the carbs and put new float needles in. They are different than the black rubber tipped that were installed. They go further in. Will report back when reinstalled.

 

Be sure to set the fuel levels again. Not all float needles are of the same height.

 

New float jet needles installed. Carbs reinstalled and black box tci swapped... problem still there, sputter and no go after 5500 rpm. Also now I have no adjustment via the idle knob its idleing at 2,000 rpm wont move when turned counter clockwise. Still have the slow to return hanging idle as well. Figuring it needs re colortuned but still not go after 5500. Voltage regulator seems pretty hot, could this be the issue? Either that or carb boots to head?

 

The voltage regulator is supposed to get hot. As it regulates voltage it dumps the excess to ground and turns it into heat (essentially).
When you had the carbs apart did you polish the slide bores? Did you check the slide fit to be sure they can't hang up?

 

Yes polished the bores and the slides move freely and passed the clunk test. I actually checked them 3 or 4 times just to make sure and they are good. This whole problem is like hitting a governor that's why I am now thinking it may be electrical. Does advance increase at 5500? I also have a cx500 and when the high speed coil fails on those you cant past 5000 rpm that's what this all reminds me of.

 

So did you do this? Or did you check that the slides don't quite clunk as demonstrated in the video?

 

Rooster, yes I checked the slides and they move well. Clunk test follows the video exactly. I am going to go through the wiring to see if there is a problem there. On the regulator plug output the red wire must have gotten hot at one time because the connector was melted there. I also plan on checking the reluctor out and wiring leading to the TCI.

 

Wires look fine. I did manage to get the idle straightened out, some things changed when I corrected the float. Still having the same issue as mentioned before. Frustrated.

 

I'm a bit late to the party but does the xj750 model carbs being talked about here have pilot screws on each carb?
Not the pilot air jet or any of the other jets but a pilot screw?
The one that adjusts fuel/air mix at idle.
Just a thought.

 

Yes they are there. I have them about 2 3/4 out via color tune. I plan on rechecking the vacuum diaphragms with a magnifying glass after reading similar stories on this awesome forum. Ive gone over just about everything, valves, sync, colortune, fuel delivery, ignition. Nothing has changed this problem and I must be missing something.

 

Were valve clearances checked?
Cam timing?

 

Valve clearance was corrected how do I check valve timing and to adjust?

 

Ok all so I went back and polished the slide bores again this time with 1000 grit. It had a positive effect. I still get a sputter at 5k but I can now at least push through it up to red line. It takes a few seconds to get past the sputter however. I still have a slow to return to idle but its better than it was.

 

Took bike out on road and max speed is a whopping 65mph. Wide open sputter. I am going to continue my quest to fix this bike. Runs great up to 5500 rpm. One thing I noticed is the carb to head boots. After I shoe goo and liquid taped the boots I ran electircal tape around them just as another seal. I saw the tape moving in one spot in and out on the number 1 and 2 carbs. Seems like air could be pushing on them. Could cracked carb to head boots be causing all these problems? Thanks everyone, this bike is diffrent from anything I have worked on and its been a challenge to say the least.

 

The bit with the 65mph and sputtering is my current issue. Let me know if you get a solution!

 

You line up the crankshaft to the T mark and check that the dots on the cams near the chain sprockets line up with the marks on the cam caps.

 

Yes. A vacuum leak will alter the fuel to air ratio, and a leak at a flexable joint will be a variable leak (the size and volume will change as engine speed changes).

 

that 5K stumble can also be from the exhaust system

 

Cam timing looks good. I'm going to check valve clearance again while in in here

 

Valves

How can I verify if the exhaust is causing this Polock? Currently bike has stock exhaust all the way back. Seems to flow just fine but hard to tell when I am on the bike under load how it is.