carb slide diaphragm

im having lots of trouble with the idle on my bike, kz440 ltd a 1980.

it has a has a hard time starting, but will usually start after a couple tries, but then the idle is all over the place, cant seem to dial it in with the idle screw. it revs high then drops so low that it will die unless i give it gas, but if i keep on the throttle the bike will get me where i need, amd occasionally can idle fine without dying at a stoplight

. i talked to my neighbor who knows bikes , and he said it sounds like my slides are sticking. so i opened up the top of the carbs and one diaphragms is wet on top, and seemingly still in place, and the other diaphragm is completely dry and was not fully in place when i took the cap off. i assumed the dry one was not sealed properly so i put it in place, screwed the cap on both sides, and started it up. idle was not fixed.

so specifically: should the top of my diaphragm be wet? or should it be dry?
and more broadly: any clues about whats going on w my bike?

Is your bike stock or modified? If modified what was done if anything to the intake system and exhaust?

If the airbox and/or exhaust is modified that will throw off the jetting and cause running problems. You might want to go through the carbs and clean them, followed by replacing all the various O-rings. Do NOT purchase junky aftermarket carb kits, just get O-rings and maybe bowl gaskets and float needles if necessary. What you describe could be cause by air leaks on the intake system too so remove all the rubber carb runner boots and inspect carefully or just replace them. The idle will hunt and creep upward if there are air leaks.

Good luck

Do the thumb test. Put your thumb over the large vent on the top back after you lift the slide and see if they fall fast or slow. If fast you need new ones.
Steve

Does your bike have the stock air box and air filter? Ed

everything is stock, and i have replaced the old boots on the carb and that did nothing. i can spray starter fluid at the carb while the bike is running and the rpms will not increase.

i will try this thumb test when i take it apart, but should the diaphragm be wet or dry?

The diaphragms should be dry. If they are wet that means something is wrong with your floats and/or float needles thus allowing fuel to overflow. That's why it's important to do maintenance such as cleaning the carbs and replacing all the various O-rings. Also, measure the fuel level following the maintenance procedure outlined in the factory Kawasaki service manual for your bike.

okay. but why would something be wrong w the floats. if the float bowl was too full, the excess would spit out thru the overflow, and thats not happening.

also the carb is very clean, i did not replace the orings, but the first thing i tried when this was happening was to clean the carb.

Have you adjusted the valves?
Steve

swest wrote: Have you adjusted the valves?
Steve

Maladjusted valves won't lead to wet diaphragms, but Steve makes a great point about performing maintenance. Trying to diagnose running problems on a bike that doesn't have all the maintenance up to date is an exercise in futility.

Any time you have evidence of too much fuel in the carbs that should automatically trigger a fuel level check inside the float bowls (using the clear tube method) AND a check of proper function of the petcock. Failed petcock diaphragm often allow fuel to back flow down the vacuum line and into the carbs.

cwhitm2 wrote: okay. but why would something be wrong w the floats. if the float bowl was too full, the excess would spit out thru the overflow, and thats not happening. . . .

The fuel level can be too high without being high enough to enter the overflow circuit.

Good Fortune!

cwhitm2 wrote: . . . the carb is very clean. . . .

Good Fortune!