Originally Posted by Southgate Jonny
Do you have a NT carb? After running Opti at 100:1 mine was 4 stroking a lot with the stock jet, I installed a 68 and it improved it the issue slightly, then I switched to a 66 and it runs way better with just a bit of 4 stroking at about 1/3 throttle and again at about 2/3. I may order an even smaller jet to see if that will eliminate the issue altogether.
running a 16mm yamaha y zinnger / pw80 carb, #70 main jet, i just got my 90deg angle air filter though so now i can tune it up. i was running a brigs and straton lawn mower filter adapted to the carb with a spacer, now that i have a proper high flow filter i can tune it with my jet kit.
on another note on the 90 deg air filter from SBP.... if you use that filter angled upwards, it keeps your filter cleaner, this is due to the blowback from the motor hitting the rubber angle instead of the filter paper ! i like it a lot !