Is the "pinch" test also applicable to 4c engines for adjusting the LSN? I have a FS91SII which was well tuned before but after sitting idle for a month or so, the thing would quit as soon as I removed the booster. That happened even after I replaced the plug. It would race with the booster on but drop in rpm suddenly when it was removed. I need to get this engine operational this week to put into a new airplane.

Also, do 4c engines compulsarily need nitro in the fuel. After a lot of problems running 2C engines on a batch of fuel containing 10% nitro, I moved to a batch with 0% nitro and the engines are now happy. I would intend to use the same batch on the 4C engines

Another thing, how do you know whether the tappet valves for a 4C engine need to be re-set?. I am recently getting a lot more misfires at WOT from the FS91SII and have never had any 4C engine before this one. I have the OS valve adjustment kit but no experience in doing the adjustment

Ameyam