StrayCats GSXR 750 Problem - Only VRF Forum Guys seem to be helpful

I continue to learn here.

todays lesson seems to be just how much of a difference in fuel level a small float height adjustment can make. unique to these BST CV carbs ? dunno

but when carb 3 was a little lower on fuel quantity, I spent alot of time re adjusting the floats to as close to exact as I could get, they were a wee bit proud on the gauge, so a bit low on fuel level. Below you see how much fuel is in that cyl 3 bowl after the slight adjustment at least 40% more fuel.

given that, I went back ad re did the other 3 as well, made sure they were all as close as I could get them to spec. We will see if they leak and then ill drain them to see the fuel amounts and it all looks ok (relatively the same across all 4 ) ill put them back in tomorrow. ....again

 

Maybe time for some clear tubes while they are still out? At lest to get them consistent with each other. Maybe when the bowl is installed, tightened and applies pressure to the float bracket it changes things a bit.

 

Unfortunately these BST CV carbs have no nipple on the drain so you cant attach a tube. thanks SUZUKI.

its just a hole in the bottom of the bowl, and the usual screw FFS

 

Can you thread an adapter, like one used for carb synch in vacuum parts?

Probably a lot of work to come up with something decent. Would be nice tho.

 

The holes are pretty small. im sure its possible maybe have to drill it.

 

IDK, im still doubtful that the increased fuel in the bowl will help. im sure it should still run with the fuel that was in it.

Ill find out tomorrow I guess.

UPDATE :


CYLINDER /CARB #3 HAS BEEN THE MAJORITY OF MY ISSUE , If one cyl drops its usually #3

Reading on this more, I read that a slightly lower fuel level in the bowl would only be an issue at full throttle, it shouldn't starve at Idle, or 1//4 or 1/2 throttle.

Im going to pull carb 3 apart AGAIN, and see if I can find any obstruction in the pilot circuit. Ill pull the mixture screw, the pilot jet, run a guitar string through it all and give it some carb cleaner again. Something is causing it to not pull fuel when the choke is off, I just have to figure out what that is.

 

2014 VFR800
2017 Africa Twin DCT
2017 Suzuki M109R BOSS
2012 CBR125R Repsol
2007 Aprilia RSV1000R Factory
2000 ZRX1100
1988 Hawk GT647 RC31
1986 NS400R
2000 Kawi Z1000
2020 Beta 300 EVO 2T
2008 Buell 1125R
2006 Buell XB9R
1997 CBR600f3
1989 CB1
1984 CBX750f
2010 R1 LE Rossi Edition
1993 GSXR750 (Current HEADACHE)



fixed that for you

 

LMFAO

 

Ha ha ha !!!


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I'm sitting here asking myself if it is possible that somehow there isn't enough air being pulled through the carb to have it function correctly. I know that sounds pretty wild, and I'd have to agree with someone if they said I was nuts.......which makes me wonder if the slide is lifting.

 

Yes Sir, the slide is lifting at the same rate as the others, I've watched that a few times.

I also checked my butterflies / bench sync again to ensure thats ok and I didn't lose a sync spring anywhere.

Im going over the same ground again tomorrow with the pilot circuit, mix screw out, pilot jet out, carb cleaner , guitar string, and compressed air. Something is stopping fuel from pulling into that cyl, even with lower fuel in the bowl it should pull fuel at idle or 1/4, 1/2 throttle ok

Of course, at this point, im still in Carb mode, but im going to switch to valve adjustment mode very soon if this last attempt fails. im not sure that will solve fuel delivery issue, but as we have said before, it needs to be checked anyway.

 

Nothing to add here but looking forward to the eventual solution.

I have learned that I do not need any of these type Mikuni carbs in my life.

Maybe NCB is right about the slides, although the slides have no effect at idle, right?

 

^^ right, jim, no effect. i suggest blasting mixture screw hole on #3 with carb cleaner spray followed by compressed air, probably something you've already tried. make sure there is no debris in the passage. i've seen a case where the small o-ring was pushed into the hole and blocked flow.

your case is one for the record books and a model for persistence.

 

Yea, thanks Squirrel, I have removed and replaced the o-rings and washers on mix screws, and cleaned the passages, but I will do that again. Is there anything else to check to ensure the air bleed for the pilot circuit is working ? just the air jet I already checked ? the pilot jets on these have no bleed holes/ flute holes in them.


while number 3 has been the most problematic, there was one time where it was the only one working. Very odd.

 

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Is this an accurate cross section of the carb?


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yea looks pretty accurate. Mix screw is on the engine side of the carb, so maybe that makes it a fuel screw. (turn out for rich) vs and air screw on the air box side (turn out for lean)

I added a diagram too, basically the same but show the enrichment circuit

 

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This one is better , it id’s the circuits.


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That slow air jet looks interesting.


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