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Hopefully someone here has an idea on this one. I have an 81 Kawasaki KZ750 Ltd. I just did a valve adjustment and compression is good on all four. Carbs have been cleaned and synched and I have checked all the holders for airleaks using carb cleaner, they seem fine. There is spark on all four as well and are all firing.

Here's the problem. It will not maintain a consistent idle speed and will die at anything under 1500 rpms. It seems like there is an air leak but I cannot pinpoint it. A quick shot of gas and the idle will jump up and hang at 4000 until I back off the idle adjuster. It then drops down below 1500 rpms and will stall out. I'm not adjusting it much either, just a slight turn is enough to drop it.

There is one thing I can't seem to understand. In my manual it shows an air suction system tied into the airbox, this is on the US model anyway, I have the canadian. I don't have this air suction system on my bike, but the airbox has the attachement and there is a hose connected to this going into a vacuum line on my carbs. Looking at bank of carbs it has the fuel line, one vacuum line going to the petcock and another vacuum line going to the airbox. The vacuum lines on the two outer carbs are plugged. Does this sound right or could the extra vacuum line be where my airleak is coming from?

It sounds like an air leak.

I know, but i can't find it. What are all the places I should be looking at?

Did you check floats? Also check (if your bike has) drain plug and seal (O-ring) on float bowl.
I am assuming that sync is good and no leaks. Are vacuum lines OK?

My GS550 had mud packed mufflers. I figure from wasps. I'm still cleanning them out.

slimcolo wrote:Did you check floats? Also check (if your bike has) drain plug and seal (O-ring) on float bowl.
I am assuming that sync is good and no leaks. Are vacuum lines OK?

Synch is good, vacuum lines are good and one float is a under spec by 2mm will fix that tomorrow. I removed the carb holders and think this may be where the problem is coming from. The holders are in good shape, clean and no visible cracks. Whatever was used to seal them to the cylinder head was in rough shape, very hard and crumbly. I cleaned all of this off and resealed them with some RTV. Will let this cure for 24 hours and see what happens.