i had a 120 on my Mitchell, ran great, but I had one problem with it that I could never figure out, had the same problem on a freinds 120 also. At idle, I could never get it to hit even on all four, you could pull the plug wires and the cylinders would drop different amounts, # 4 wouldn't even make hardly any difference, went thru the carbs numerous times, set the linkages per the manual, double and triple checked the linkage and settings, then went back and set the linkage so it would idle, ended up taking the idle speed knob all the way out to set the idle timing up enough so it would idle in gear. I checked the reeds, OK,made sure no one had mixed up the airbleeds and jets, spark and compresion were ok. Thought it was just mine, till my buddies did the same thing, even swap carbs from another motor and it made no difference. I never did get in to changing idle jet sizes(did'nt have enough to go experimenting). Got it to run good enough, but was never completely satisfied with it at idle.