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Johhny5 carb help (ZX6) ? anyone
jollygreengiant - 13/4/09 at 03:41 PM

I have just been over to see johhy5 where he is building. He has a problem with his bike carbs. He is using ZX6 carbs but I think he has a fault with the carb for Number 4 cylinder.
The engine now ticks over fine (timing adjusted and carbs reasonably balanced), however when you accelerate the engine the slide/piston on number 4 cylinder fails to raise like all the others. I have pulled the top cover off and had a quick look at the diaphragm. This looks reasonably OK with no obvious splits or holes. Neither does there appear to be any air leaks, the engine base idles too well for that.
However, when you just gently lift the piston (with the engine OFF) there is a noticeable (lower/less) difference in the effort required to lift the piston compared to the other 3. It is almost as though there is diaphragm.

I have never played with these carbs before so I am on unknown territory compared to a lot of you out there. Is there something simple that I have missed.

Your opinions would be gratefully accepted.

rusty nuts - 13/4/09 at 03:47 PM

Is it worth swapping the piston and cover from one of the other carbs to check if it is at fault ? Could it be an engine or intake problem?

jollygreengiant - 13/4/09 at 04:03 PM

quote:
Originally posted by rusty nuts
Is it worth swapping the piston and cover from one of the other carbs to check if it is at fault ? Could it be an engine or intake problem?


I did think about doing that but I didn't want to disturb the other pistons/diaphragms in case I made matters worse.
I am fairly sure that it is NOT an engine problem as it idles TOO well for that and he has a nice even colour on the stainless exhaust pipes which tends to indicate an even Idle burn across all 4 cylinders. It is ONLY when you accelerate and hold higher revs that he starts to get unevenness
and a misfire on number 4. It is drawing a good vaccuum on that cylinder because you can see the fuel being pulled out of the main jet around the needle. Its just NOT lifting the piston. Even without the balance spring in the top of the chamber.

rusty nuts - 13/4/09 at 04:19 PM

Air leak at the diaphragm?

johhny5 - 19/4/09 at 08:50 AM

Sorted it,
just needed to put a little grease around the top of the diaphram and the plastic cover to get a good seal, now working good , cheers
John