Back in the day I used to tune my '69 Z/28 by hooking up a tachometer under the hood and setting the mixture screws until I got the highest idle. That was the last thing I did after replacing points, plugs and setting timing. Worked like a charm, the pipes were always a light grey color indicating a good burn. Not too lean, not too rich. And, upon spending countless hours driving an Allis-Chalmers D17 tractor in circles in field after field, I noticed at quitting time that it was quite a clean burner as well.

My '75 shovel motor isn't a Chevy small block nor a straight four agricultural motor. But I can't help but wonder about the exhaust color. My pipes are black, and when firing it up in an enclosed area the fumes tell me it's running pretty rich. Is a light grey exhaust deposit something I want to see with the shovel?

 

the real answer is in the history of the machine - it is 45 degrees the V twin and has a single crank pin - the ignition is not balanced like a real 2 cylinder engine BUT -- AND again but its what fit inside a bicycle frame sooooo it will never give you what you are looking for