Some carb issues (my guess, false air)

First of all, i've searched the forum a 100 times (maybe more ) and couldn't find the solution.

My XJ650 just doesn't want to run how it should, won't idle and runs very irregulair around 1100rpm (with or without choke). Doesn't rev as fast as it should and doesn't back down fast enough. The inlet manifold are air tight because another set of carby's makes the bike run perfectly smooth.
Installed a rebuild kit with new float needles ed. Set them to the correct hight (after they flooded and filled up my carter :roll Carbs can't get any cleaner anymore.

I'm starting to think that the sealings around the butterflys are leak, because when I rebuild them they where to small. Couldn't get new ones but after I let them soke in some fuel for a couple of hours they became even a little to big so they looked like they made I thight seal. Spraying some brake cleaner on it doesnt change anything though, but if the bike runs this irregulair i'm not suprised.

But before I dismantle them again maybe some of you have an oppinion about this?

Other set of vac-slides didn't change anything either btw.

 

Gais,
You may want to check the thin rubbers on the top of the slides. They can develop thin holes in them that are not easy to see. Just take the tops of the carbs off and you'll see them thin diaphrams I'm talking about. PD

 

I know what you mean but I checked them with a light before I put them in, even changed them with another set to be sure.

I decided to put new seals on the throttleaxle, checked the ones on the outside last night and could pull them out withouth trouble. Expensive for a tiny bit of rubber but I don't know what else it could be anymore.

 

Sounds like it needs a carb sync done. Especially if you have plled them apert to change the butterfly shaft seals.

Out of sync can cause the symptoms your describing.

Can you just use the other carbs you tried or were they just a loan set.



Can tune it for you in september when I'm over there if you like.

 

Time for an update. The other carb set came from my fathers bike so I couldn't use them.

Replaced the butterfly seals, fixed some other tiny problems but it didn't work out. Got so fed up that I didn't do anything on the bike for a few months.

But i'm proud (and frustrated) to announce that I think I found the problem.

Here is a picture of an airscrew (actually a gas screw right?) with a damaged tip. Hardly visible with the naked eye but I replaced it with another and finally the bike starts to react how it should. That was yesterday, today I did a cold start. Fired up nicely, with a little bit of choke it ran a bit irregular around 1100rpm but she reacts real good on the throttle and fall right back to idle and doesn't cut off. Finally i'm getting to the finetuning part, going to borrow a colortune and carbtune for that.

Here is a link to the picture (1,1Mb!)

 

Did you also replace the spring, washer, and o-ring?

 

Thats the needle, a damaged needle could be a frustrating problem.
Good to hear you are proceeding now, get her tuned right and that idle problem will go away too

 

Didn't replace the o-rings or springs, just put good ones them in (got several old carbsets laying around)

But finally things start to come together. Borrowed a color and carbtune, rememberd that I still didn't replace the exhaustgaskets so I replaced them and now she finally starts to run how it should.
Idle is a bit high (idlescrew doesn't touch the throttle axle) but she sounds almost spot on (just a tiny bit irregulair) Sync is still a bit off but the engine needs to cool down a bit before I can continue.

Going to get some front fork oil, put the wheels and brakes back one so I can take her out for a little spin.

 

Tried a colortune but still couldn't get her to idle, guess there is still something wrong.

Didn't hold me from trying it out on the road and after the bike get some heat in it she starts to run pretty good. Main jets are to big so when I open the throttle to much she starts to hold in but if im gentle on the gas she pulls without hesitation from idle. When my Dynokit arrives I pull the carbs open again to inspect them again.

Does the mainjet got any influence on the idle circuit btw?

 

main jet kicks in at ~3k rpm(rick comment here plz)

I think you might have to bench sync those carbs again. If the idle rod does not make an impact on idle.

I hear good things about using a business card for that purpose of bench syncing.

Once the idle adjustment rod is working, time to SYNC and ADJUST MIXTURES

And then do it over and over again

What size jets do you have now?

 

Idle rod does have an impact, when I set an idle speed with it (warm engine) and hit the gas it takes a while (a long while ) for the engine to get back to idle speed. Carbs are synchronised with a carbtune, tried the colortune but I don't get a read out at idle speed so somethings wrong. When I tried to set it up anyway the pilot screws where 5a6 turns out(!), bike idled without the idle rod touching but the same slow fall back again.

For my testrun ive put the screws around 3 turns out, idle rod to low to keep it idling but the engine responded good. Falled back right away and pulls good from low revs. Only if the revs got to low (below ~1100rpm) it was hard to get them back up again.

Conclusion, theres still something not right and I missed it a thousand times. But I wait until I get my dynokit before I pull the carbs out again so I can do it the same time, pulled them off so many times (also with other bikes) that it is something I really dont like
Running 126 main jet btw, far to big.

 

Decided to open the workshop manual for a change to investigate how the carbs work exactly. Got a nice picture where all the channels are visible.
Main jet doesn't have any influence at the idle circuit.
But I have some clues what I can check when I pull the carbs back off.

 

well the float levels could be set TOO HIGH as well.
make sure the levels are within spec.

the idle speed of these bike is ~1050 rpms. set that adjustment rod to keep it from going under 1050.

the mixture screws can be set @ a default of ~2-3 turns out. Then the sync can be performed.
then it is a bunch of mixture adjustment then syncing over and over again
time consuming, but eliminates the colortune process.

as the sync and mixtures get to a more perfect spot the idle adjustment will need to be tweaked again as the carbs are performing more efficently.

one adjustment affects the other <sync & mixtures>

 

Yes, the xj idles! Still need to setup the pilot screws and synchronise but she just keeps on running. Could even walk inside to get a camera to film it

Installed a Dynojet, blew everything true (again) with compressed air, even flattened the seats of the jets with a wet-stone to make sure it doesn't leak there.

 

congrats
get started on that tuning now.
sync...
mixtures...
repeat.