Mikuni BS34 problem

I'm proud owner of 1984 GPZ750.
Bike is in stock, except for the L&W 4-1 exhaust. Stock airfilter also.
All jets are stock, main is 110.
Bike used to run well, and rev to the red zone with no problem.
I had a problem with choke, and removed float bowls, cleaned all circuits.
I discovered that float level was WAY high, and returned floats to 18,6mm (factory). Did not mess with mixture on any other adjustment.
Returned carbs on bike. Engine starts perfectly, choke working, but she won't rev over 5000 in any gear. Even in first. Works well until that, and then like it hits rev limiter. Tried to put petcock on prime, nothing. Replaced spark plugs, nothing. Tried to pull the choke, nothing. Tried to remove airfilter element, even worse!

Some people suggest me to put larger main jets. As i know main jet only affect from 3/4 of throttle to WOT. My problem starts to happen on only one third.
Also, if i put WOT, engine dies during driving. Putting throttle to half, returns me to "rev limiter", and on quarter bike works normally.

Help needed.

im not an expert but it sounds lean or you have a vacuum leak did this happen after the exhaust change or was it sudden ? what color are the plugs burning

Key notes to LEAN condition..... "Bike used to run well, and rev to the red zone with no problem. " & " discovered that float level was WAY high"....

Maybe this will help you diagnose your symptoms....

Basic rule of thumb for 4-1, pods (I realize you're using air box), non stock configuration jetting etc....







Follow this link for BS 34 re-build/tuning... One of the best write ups w/images I've come across...

BS-34 Rebuild....

The exhaust came with the bike. Never used any other.
Spark plugs looks okay. Dark brown.

If not already done, would assure that the ignition timing advancer is properly functioning and not stuck in the idle position.

markovis07 wrote: ...discovered that float level was WAY high, and returned floats to 18,6mm (factory)....(

Would also perform the clear tube test on each carb to assure correct fuel levels.

"Float height" measured with carbs on the bench is not a reliable manner to assure correct fuel levels.

So long as fuel level is within specs, it doesn't really matter what the measured dry float height happens to be.

Good Fortune!

Think you missed the point....

Just because the 4-1 exhaust was on when purchased doesn't mean it was jetted correctly...
Case in point, float level was off thus extra fuel to compensate for the lean condition of the exhaust...

You adjusted float levels to spec now issues (more air than gas)....

Old Man Rock wrote: Key notes to LEAN condition..... "Bike used to run well, and rev to the red zone with no problem. " & " discovered that float level was WAY high"....

Maybe this will help you diagnose your symptoms....

Basic rule of thumb for 4-1, pods (I realize you're using air box), non stock configuration jetting etc....

Follow this link for BS 34 re-build/tuning... One of the best write ups w/images I've come across...

[url=http://kzrider.com/filebase/doc_download/508-mikunibs-
cvcarburetorrebuildtutorial]BS-34 Rebuild....[/url]

great rebuild/tuning article :side: thanks for the link

My 82 GPZ750 has run all stock jetting and needle settings since it was brand new with a $90 RC Engineering 4-1 pipe I put on it when it was a month old. All Ive done is uncover the mixture plugs and richen them 1/4 turn plus synch them. Still runs perfect and Ive cleaned the carbs several times due to plugged pilots jets. Are you absolutely sure youre measuring to the correct point on the carbs for float height ? Have you tried running it on the manual prime position, perhaps the diaphragm could be going bad in the vacuum petcock ? You might have also cut an airbox boot or something removing & reinstalling the carbs. Good luck with it.

Are you trying to run it without the carbs attached to the air cleaner?

No, the carbs are hooked to the airfilter housing.
I guess you're right, that the high fuel level compensated for the small main jet.
I've got good fuel flow, petcock works ok in all positions.

How do the diaphrams look.

Hang on a minute. The bike ran well with the stock jetting. (so leave the jetting alone for now). There was an issue with the choke so you pulled the bowls. While you were in there you fiddled with the float height and set it to " floats to 18,6mm (factory). " What the heck kind of float height measurement is that supposed to be??? Trying to set the "Float Level" is an exercise in futility unless you go back and correctly set the FUEL level using the clear tube method as described in the Kawasaki Service Manual and on this site. You really need to do the clear tube process to CORRECTLY set the height of the FUEL. Otherwise, if the fuel level is too low you can change jets until the cows come home and not solve the problem because the engine cannot run at high rpm if there is not enough fuel in the carb bowls. Ed