idle screw adjustment

Hey everyone
Since I got my 81kz550 running, everytime I turn it on I have to turn the idle adjustment screw on the carbs in. Once the bike's been running for a few minutes the rpms shoot way up and I have to get off the bike amd turn the screw back out. If I turn the bike off and let it cool down the idle screw needs to get turned back in before it will idle. Any suggestions as to what could be wrong?

The first thing you need to do is clean the carbs. Then you need to set the idle mixture screws after you synch the carbs.
What you are experiencing is neither normal nor proper.

Also, be sure to test for vacuum leaks at the carb holders. They will eventually develop tiny cracks in the mating surfaces between the holders and the cylinder head that can cause them to leak at idle. These cracks cannot be seen with the carb holders in place. As the engine warms up, things expand and the leaks can increase or decrease. I suggest you try the following. Get the engine warmed up and temporarily set the idle as low as possible without killing the engine (lower than 900 rpm if possible). The lower the better because with the idle very low the slides are nearly shut and the vacuum inside the carb holders is at its highest. Then spray carb cleaner around the carb holders, especially where they mate with the cylinder head and where the carbs attach to them. Carb cleaner works best for this test as it doesn't leave an oily mess with WD40 or evaporate so quickly that it is not drawn into the leaks as can happen with propane or starting fluid (ether). If the engine dies or reacts to the carb cleaner, you need to replace the carb holders. Carb holder leak related problems are noticeable at idle but generally don't have much impact when riding because the throttle is open. If you find you need to replace the carb holders soak the screws with Kroil for a couple days before attempting to remove them, and use JIS standard, NOT Phillips, screwdriver bits, and this will greatly improve the odds that you will not break or strip a carb holder fastener as so many have done. Let me know if you you need info on JIS bits, I have a good link for making your own at no cost.

I agree ed, but usually a vacuum leak will result with an idle that will steadily increase and not be able to be decreased until the leak is corrected. But certainly something that must be checked. I use starting fluid, where others use WD-40 to investigate leaks.

You might want to try using carb cleaner next time. I had suggested that to another member of this site who found no leaks using starter fluid, and he said the carb cleaner revealed the leak right away. He said the problem with using the starter fluid was that is was evaporating so quickly it wasn't being drawn into the leak in enough quantity (if at all) to affect the idle, but the carb cleaner evaporated much slower so it was drawn into the leak. Ed

Almost any product's spray mist would be okay that results in a noticeable change in rpm when ingested through a leak into the air-fuel mixture being drawn into the combustion chamber.

Sometimes the rpm change is easily detected, but under other circumstances may be more difficult to detect, for example where the engine won't idle down to a very low rpm for test spraying.

While WD40 may leave a residue (that's relatively easy to clean off), an advantage of using WD40 spray as the test medium is that smoke from the exhaust is visible (in addition to any rpm change) to confirm ingestion of the spray.

I don't know whether ingested carb cleaner spay smokes as much from the exhaust as does ingested WD40.

But the visible confirmation of smoke from the exhaust is helpful when rpm change is doubtful or inconclusive.

Good Fortune!

When I tested my old leaky carb holders I set the idle down low (about 750 rpm). This caused max vacuum inside the carb holders because idling that low the slides are pretty much closed. When carb cleaner was sprayed around the carb holder/cylinder head joints the engine stopped running. That was pretty strong evidence of carb holder leaks - no smoke needed. :laugh: :laugh: :laugh: Ed

Thanks for thr replies everyone. The carbs were gone through and cleaned 3 times with carb spray, air , and a wire brush
They have new gaskets, jets, ans needles. The previous owner screwes the intake boots down way too tight to get them off the bike if i do find a vacuum leak when I test it later. If I try to take them out theres a good chance I'll strip the screws. Any ideas on how to get them out without stripping them?

Just tested for vacuum leaks. There is one small leak on the #3 boot but the rest are still good. I just started it up with the choke on and it seems to warm up faster and not require the idle screw to be turned. I figured the summer heat would be enough to keep the bike from needing choke. Is this still a problem or is it normal for Kzs to use choke every time they've not been running?

I think it is pretty normal for all carb engines to require a bit of choke when the engine is cold, even in the summer heat.