84 Gpz750 Carb Problem

Just installed new carb boots front and rear. The idle on the bike goes up/down by itself. If I put my hand over the airbox hole it'll rev up to 7,000? I have a portable gas supply hooked up to the carbs and the vacum hose is plugged. I sprayed WD40 around all the boots looking for air leaks, but none. The throttle cables are not binding and the throttle snaps back into place.

The bike shop did set the float levels (they say?) Could improper float level cause the erractic idle?
I also noted that there are no rubber plugs over the pilot jet. The haynes manual shows a rubber plug?

I'm tempted to put my 92 ZX6 carbs on it!!!

i6.photobucket.com/albums/y217/gaillarry/16Sep002.jpg

Post edited by: gaillarry, at: 2007/09/16 16:42

Post edited by: gaillarry, at: 2007/09/16 19:24

Hand over the air box hole = less air, enriching the mixture. The WD trick was a good idea, in my opinion.

Don't think the float level is the problem, I found it hard to get mine wrong. Way to check: go to local hardware store and pick up some ---ummmmm--- do I want to say it is 3/16 clear plastic hose, a foot would work. I think I attached the hose to the bowl drain in the bottom and ran the hose up against the carb body, up in the air. I put my petcock to prime, and opened the screw for the drain, and looked to see if my gas went up to very near, but not quite, to the junction of the bowl and the rest of the carb. The exact specs are in my manual, and I don't know where that is.

That being said, I don't think the float level could do that. I can try to expain it, but it would not be very technical. After a ham fisted unknowledgable adjustment, my floats looked like they never cut the needle off, and I still ran the bike for a while with no erractic idle.

I'd say that your carbs are out of synch, trying to fight each other. The question is why? The reving makes me think that the jetting is not right or not clean enough. Maybe compression, maybe valve clearance. (I know on my bike with one cylinder down 40PSI from the others, and before I redid the carbs right, would start in the cold better with the hand over the airbox.)

I never put rubber plugs back over the pilot jet on my carbs.

Please put your other carbs on it, I love to see hybrids that way. Don't know if it would work, and many may say it won't, but sounds like fun to try to me, especially with new boots.

Still sounds like you have a vacuum leak somewhere, with that idle fluctuation. Only when cold? Only when hot? I'd bench-sync the carbs as recommended first, then set the air mixture screws the same. I believe with all stock components, they should be 2.5 turns out. Check the front carb hoses/caps, as you might have a leak there.

Good luck.

Finally got around to working on the carbs. Pulled them, cleaned them again, put on new vacum ports, new o-rings on the air screws. Bike idles good but the revs will hang up on throttle, and slowly return to idle. I checked for air leaks again with carb cleaner and no change in the idle.

Out of curiosity I removed the caps on the vacum slides to see if one was binding or hanging up, but they moved freely and no tears in the diaphrams. When I put the caps back on and started the bike the reving problem was gone. Bike idles great and no hang ups on reving.

Until.... I took the bike for a test ride, ran great, lots of power, no reving problems. when I pulled into the driveway the revs stayed at 3000+rpm. I checked the throttle cables for binding, but they're ok. After a few minutes the engine dropped to its normal idle.

I did remove the pipes to put a new starter clutch in but didn't change the exhuast gaskets. Could an exhuast leak cause the over revving?

Since the exhaust gaskets are crush-type and are intended to be used only once, there is a good possibility that your air leak is coming into the combustion chamber via the exhaust runner. Also, you should see some VISIBLE slack between the cup on the bracket that holds the cable end and the bellcrank. Last, check to see if the sync mechanisms are catching on the screws on your carb holder clamps.

There's lots of slack on the cable and no binding. I took the bike for a ride today and it ran great!!! I have new exhuast gaskets on order. Hopefully they'll prevent future issues.