CJ750 toolbox

Useful information on carburetors

An interesting experience that Jim Middler had

"One thing you should be aware of. I am not sure if the Mikunis have the same problem or not but I would expect them to. I was using the other non-CJ carbs for awhile and ran into this. My petcock leaked and a lot of my fuel ended up in the engine. I have a 29 litre fuel tank that was almost full and didn't run the bike for more than a month (was out of town a lot). I ended up with an oil/gas level in the crankcase high enough for some to remain in the cylinders and hydraulic lock them. The original CJ carbs will just leak out of the float bowl and not run into the engine. Also, the M1 petcocks are much better quality (hard to believe, eh?) than the petcocks on my big tank and not so prone to leakage. If you run your engine regularly it should heat off any fuel that does drain in. The fuel is thin enough that it is very difficult to identify on the dipstick so just checking the level is not reliable."

Excellent technical information from Phil McKinnon

"You may be interested to know that Wolfgang in Shanghai claims he has flow-tested the old carbs and found most of them have a jet orifice too small. He claims that for the airflow, volume, etc. of a CJ (and he has an SV) the jet should have an orifice of 1.05mm yet when he tested them he found sizes from 0.7-0.9mm. He says if you drill the jet out (obviously in a drill press) with a 1.0mm drill bit, it will give you almost exactly 1.05mm. According to Wolfing this will give you as much boost in performance as the Mikuni knock-off carbs. I haven't done this but put the knock-offs on my OHV and did for sure notice a big increase in upper end response and 4th gear roll-on, especially above 50-60km/h (30-40mph) with standard gearing."