After clean up my '97 Kat 600 and reassembled everything, it starts, runs ok for the first 20 to 30 min. until it's well warmed up, then the idle become unstable. first shot up to about 4 - 5,000 rpm. if I try to lower the idle, it will die. #3 and #4 are easily synched, but #3 and #4 are not. #4 always have higher vacuum than either #3 or #2. I was using homemade manometer with 2 bottles connected together. Any advice is appreciated.

Hello, welcome to KR.

I have an 06 Kat, so my carbs are a little different than yours. On mine, one of the vacuum ports is larger than the other 3. I bought a sync tool, and it uses inserts in the tubing with very small holes as restrictors so that the vacuum pressures are read, rather than the amount of vacuum flow. That might be a bad description of it, but the restrictors even out port size difference.

That said, I think hanging idle is often caused by a vacuum leak. Maybe you have an intake boot or two that are fine when the motor is cold, but once it warms up, starts to have a leak. Hopefully other people with more experience with that kind of problem chime in.

If you try to search for info, use the google search option, as it produces better results.

Again, welcome to KR.

Welcome to KR

Welcome to KR. Carb setup, or vac leak could be your issue.

Welcome!

Welcome to KatRiders.