GSX750ES REVS SUPER HIGH AVTER INSTALLING CARBS

[SATANSAM]

Hi amigos,

I installed the carbs again, like always, and the revs just wont turn down! round 2500 to 3000 rpm idle, choke not pulled, idle screw without touching the accelerator arm or however you call it....Mixture correct, and to be "correctly balanced" it has to reach more than 3000! I', totally lost....

Any ideas? Thanx

[wraith]

Throttle cable ?

[Captain Chaos]

the easiest fix is an oilcooled 1100 engine and a turbo.

[SATANSAM]

8 minutes ago, wraith said:

Throttle cable ?

No....I wish! 

[SATANSAM]

2 minutes ago, TonyGee said:

looking down the bore of the carbs are all the throttle butterflies fully closed ?  if so it could be an air leak. 

Going to disassemble them again  

[wraith]

Was it doing it before you removed and striped them?

[SATANSAM]

13 minutes ago, wraith said:

Was it doing it before you removed and striped them?

No it wasn't! 

[Pudzrx]

Sounds like you have got a butterfly the wrong way round , or if they are cv carbs , a split or leaking  diaphragm maybe . Sticking float or poorly set float heights over fuelling and revving , or a massive air leak on  a carb runner ?

Only needs to hang one carb up to make all 4 rev.

Puddy

Edited November 30, 2020 by Pudzrx

[SATANSAM]

9 hours ago, Pudzrx said:

Sounds like you have got a butterfly the wrong way round , or if they are cv carbs , a split or leaking  diaphragm maybe . Sticking float or poorly set float heights over fuelling and revving , or a massive air leak on  a carb runner ?

Only needs to hang one carb up to make all 4 rev.

Puddy

Thanx Puddy!
It sounds something like that, I'm going to disassemble the carbs and and see...I sprayed the intakes with brake spray, it changed idle a bit but not that much...I've got another clean carb set to fit in and try...Thanx! 

[SATANSAM]

I've got 2 sets of carbs, so I cleaned the 2nd set, installed it, started the bike and CORRECT (not correctly carburated but low rev). Uninstalled this 2nd set and Installed the original set and wallah = over reved...So it must be something to do with diaphragm....Pilot jet (One was faulty and wouldn't come out)...Who knows, but gonna install the 2nd set and restore the original one I supose. Thanx guys.

 

[SATANSAM]

Hi amigos,

I was thinking...Could it be valve clearence out of place? I did it a month ago but maybe by some reason it's out of place. I try to balance all 4 carburetors and the cylinder number 3 (the one without synchronizing screw) doesn't vacuum as much as the rest....Things I'm going to re-look:

- 1ST COMPRESSION IN ALL 4 CYLINDERS

- 2ND I CHANGED THE FUEL PIPE FROM TANK TO CARB...MAYBE IT'S TOO BIG? (6MM)

- PILOT  JET AND DIAPHRAGM IN THAT 3RD CARB...

Thanx guys....I'm going to a psychiatrist, he might help!!!!! 

[Gixer1460]

First, if you think the valve clearances might / may be wrong - check them before anything else! They don't 'slip' unless assembled wrong or adjusted badly.

Balancing carbs - the non adjustable is the reference - if it has the lowest reading, the others have to be adjusted down to match - that is the correct way.

Compression check - no bad thing although what it tells you is minimal.

You can't 'over' pipe fuel to a carb! It'll only take what it needs. On the other hand 6mm is borderline small not big! 

Don't fuck about with the only carb that is likely running correctly!

High rpm's is usually air related - air leak or throttle butterflyies open too far or stuck open and can't close. Its fault finding 101 !

[SATANSAM]

6 hours ago, TonyGee said:

you said you fitted a second set of carbs and it was fine but when you put the first set back on it over reved, so the problem lies with the first set of carbs. 

Yep! The thing is that 2nd set of carbs leak as hell, even with gaskets changed and floats with correct height...Weird...But what I saw when balancing the carbs was that when I tuned number 2 carb to the 3 (reference carb) the bike reved up more, and when adjusted the rest just imagen...That's why I think the 3rd reference carb has a leak or something...I've got clean pilot jet and diaphragm to try...Thanx again guys

 

[SATANSAM]

2 minutes ago, TonyGee said:

when you balance carbs it can alter the rev's up or down, if it does alter the rev's you adjust the idle screw. 

Yes, but the idle screw is totally unscrewed (not even touching the throttle slide)

[SATANSAM]

3 minutes ago, TonyGee said:

ok, are all the butterflies fully closed ? 

Yes, I've got an appointment with the psicho, I'm round the bend! 

[SATANSAM]

1 minute ago, TonyGee said:

if all the butterflies are fully closed it can only be an air leak.  what bike/carbs are we talking about ? 

Its a GSX750EF '86 with 4 Mikunis like these...

[SATANSAM]

9 hours ago, TonyGee said:

have you fully stripped them ? they'll need a full strip down and check for ware and make sure all the drillings are clear, also the diaghrams are not split.  make sure the needles arn't loose in the slides. 

I stripped them but I dodn't make sure if the needles were loose or tight....I'll do that today and I'm going to fit another clean pilot jet from the other carb set just in case.

Thanx Tony!

[wraith]

The second set of carbs that run ok but leak even with new seals and float height set. If they still leak it most probably be float needle's that are worn and not sealing or just a spec of dirt in there, doesn't take much.

[SATANSAM]

30 minutes ago, wraith said:

The second set of carbs that run ok but leak even with new seals and float height set. If they still leak it most probably be float needle's that are worn and not sealing or just a spec of dirt in there, doesn't take much.

Thanx wraith, I don't know much about carbs and I thought maybe there were rubbers inside conecting each carb that maybe dyed up by not using them...But yes, I'll give them another try too...Crazy stuff! 

[SATANSAM]

Thanx Tony!

[SATANSAM]

Well, I started the bike again before disassembling the carbs, sprayed propane round the manifolds and airbox with a blowtorch (Correct) Disassebled the carbs - I changed pilot jet for a another one that I cleaned with vinegar, petrol, solvent, spit, piss, compressor gun and god know what else...Inspected the diaphragm and it was correct...So was the needle...So I mounted the carbs in, starded the bike and it didn't rev up! It actually stalled when I inscrewed the idle screw...So, I think the refference carb (3) is now correct with low revs at last (I think it was the carb) I'll get the mixture done and then balance...Fingers crossed....THANX AGAIN FOLX!

[SATANSAM]

Well, all the same....Installed the carbs, high revs, unscrewed the idle screw until it din't touch the swing throttle arm, released each balancing screw (the 3 of them), mixture more or less in it's place blablabla...but for the carbs to be synchronized the bike has to reach about 3000rpm!!! Crazy...No air leaks anyware, nothing.....

As you can see, in the pic with all 4 gauges cylinder 3 hasn't got as much vacuum (it could mean there IS A LEAK SOMEWHERE!)....theres no way I can get all 4 the same, that's the closest I can get and over reved...Tried with new ignition coils and everything the same....All electrics are correct (I even bought another 2nd hand rectifier in good condition)...

Man, frustration isn't the word.....If any of U still have any ideas Lemmy know...I'll be in the pub drinking  directly from the tap.

Thanx again amigos 

[TonyC]

If the bike seems to to run OK at 3000 rpm but runs poorly below that I would suspect that you still have a blocked pilot/bleed jet.  At 3000 rpm the fuel will be metered by the needle jet and the mains, which being big holes are unlikely to block!  Below 3000 you are in small jet territory. I would suspect the small jet behind the rubber bung/plug next to the main, it's very prone to blocking, especially if your rubber plugs have been hardened by the ethanol in modern fuel.

Hope this helps.

TonyC

[Askamaskinservice]

You have blocked of the vacuumport to tank, in the carburators.

[SATANSAM]

On 12/12/2020 at 3:25 PM, TonyC said:

If the bike seems to to run OK at 3000 rpm but runs poorly below that I would suspect that you still have a blocked pilot/bleed jet.  At 3000 rpm the fuel will be metered by the needle jet and the mains, which being big holes are unlikely to block!  Below 3000 you are in small jet territory. I would suspect the small jet behind the rubber bung/plug next to the main, it's very prone to blocking, especially if your rubber plugs have been hardened by the ethanol in modern fuel.

Hope this helps.

TonyC

It helps, thanx again Tony... By the way I found a cool short video with this same problem: