I've got an '82 Gpz550 that I've upgraded with a Dynoman 615 kit and a MAC 4-1. Last summer, I was playing with TM-27 carbs, but they wouldn't idle right. Start easy, but give it any gas and the RPM would shoot to 4500-5000 and hang. I ran through every size of pilot jet that Mikuni makes, and while I could smell the mix get richer, the behavior was absolutely identical in every case.
srsupertrap
was extremely helpful in this process, but I never solved it.
Here's the thread:
www.kzrider.com/forum/forum-index/3-carb...50-mikuni-flatslides
I've put the stock carbs and airbox back on (with stock jets right now), and the behavior is *exactly* the same. Starts with some choke, is able to idle. Give it any gas, and it'll shoot to 4500-5000 rpm and hang there. If I put it in gear and drag the clutch, it'll bring the RPMs back down.
This seems like an air leak, but I really, really don't think this is an air leak. Boots on the head and airbox are all new. The airbox is intact, and I've sealed up the holes. What's more, I tried without a filter just to see (simulating a big airbox leak) and the behavior was *exactly* the same. I also put the filter back, duct taped over half the intake port (which should make it richer) and the behavior was *exactly* the same.
The other thing is that it seems very weird that two sets of completely different carbs would have such identical behavior.
I sprayed WD-40 all over. I tried propane. Nothing indicated an air leak.
Same behavior with throttle cable completely disconnected.
I've turned the mixture screws from fully closed to 4 turns out. The idle will smell richer and get a little rougher, but the behavior will be the same.
I have checked and re-checked valve clearance.
I have checked that the carbs are balanced.
I have checked the spark advance with a timing light, and it's a brand-new advancer unit. Moves smoothly by hand, and I can see it expand and contract with RPM.
One small possible clue is that the idle speed screw doesn't have much effect. When the idle is "normal", it takes like a quarter turn to change the idle speed noticeably. Giving it gas causes the exact same behavior, regardless of idle speed screw though.
What else could I possibly be missing?