Hi all.

I am wondering if the experts here can help. Long story short, after a crash, my YS 120FZ was repaired by me. However, most of the gaskets were intact, so I didn't have to replace any. After a long while of sitting once repaired, I tried to start it today using wildcat 20-20. It wouldn't start. I had to drop fuel into the carburetor to get to start. Once
it did, it will not idle at 2000 RPM as it used to before. Once started, it jumped to anywhere from 4000 to 5500 RPM, and surges up and down. Sometimes it drops down to 2200 RPM, then it either stop running or surges back up to 5000. I had checked the throttle linkage and setting for idle on the engine itself, all is fine. Would it be possible there's air leaks, or gasket leaks somewhere to caused the engine to idle so high and surges like this? Thank you for all the inputs.

Check the diaphragm.

Hi.

I looked at the diaphragm, it looked supple, soft and there's fuel inside of it. The plunger moved easily when i push it up and down inside the regulator unit.

They can develope tiny pin holes sometimes overlooked.

Yup !! The pin holes can be soo small you can miss them w/o a magnifying glass. When in doubt, change it. Good luck

Sounds like a vacuum leak possibly from a small, undetected crack in the case. My be at one of the mounting lugs. Had that happen to my Saito 91.

Thanks for the tips gents. I will replace the diaphragm and all gaskets to see if it would work.