71 Rochester Monojet MMV Carburetor tuning

[trevarthan]

Originally Posted by Wrenchbender Ret

You can do minor adjustments on the mixture by adjusting the metering rod height. The instruction sheet tells how to measure & adjust it. The measurement is usually about 1/16 in. If you bend the lever down a bit it will lean it out. Make sure the float level is adjusted correctly & the float not soaked up with gas. Check your ign. timing also. You usually can set the timing a little higher then specs to run better.
George

You are absolutely correct. In this case, even though I had the metering rod height set to spec, it needed to be a little higher. I don't know why spec isn't accurate here. Maybe it has something to do with the gasoline mixtures we run these days?

I ended up buying a remanufactured carb from Autozone and tossing that on just to see if it was tuned better. It wasn't. That carb ran way lean. I cracked both carbs open and compared the metering rod height. The carb we had rebuilt was set to spec. The Canadian rebuilt carb's metering rod was about 3mm higher. We split the difference and lowered the Canadian carb's metering rod about 1.5mm and installed it (I liked the Canadian carb better because it came with a nipple on the float vent and mine didn't have one).

After running this for a few days and pulling the number one spark plug it looks nearly perfect, so it seems we nailed it.

Thanks for the advice!