Originally Posted by Capt. Quirk
I don't understand the relationship of larger fittings = better carburetion??
it is better fuel pump action or performance. With the small fittings with a tiny hole in them, there wasn't enough of the crankcase pulses getting to the pump diaphragm to allow it to pump good. With the larger fittings and bigger holes, the pulses are stronger and the pump now pumps really good and then the carburetor works good.
So the carb is actually not bad, it works well when it gets a good fuel supply.
I think what happens is as the engine displacement gets smaller and smaller, the crankcase pressure pulses become more and more weak. So what might work OK on a larger engine doesn't work well when the engine is smaller. So the fittings need larger holes in them to allow for more of the pressure pulses to get to the pump diaphragm, so the pump will pump fuel better.
It just took me longer to figure it all out and come up with a fix for it on the 9cc engine.