performance carb problems

whenever i try putting a larger carb on a moped, it always seems to do more harm than good, no matter how much i play around with the air/gas adjustment it either wont go as fast, idles really high, or just plain runs poorly. any suggestions?

RE: performance carb problems

have you checked you jet screw? it might be too large or too small. i have a dellorto 14.12 carburator w/ a 55 jet (i'm hitting a bit over 30mph). also check that you have a large enough manifold, or else you won't get the fuel into the engine itself, which will slow you down. finally, you might even want to change your piston and cylinder to a larger size. i did that also before the carb change (i had a dellorto 14.9) and gained about 5 mph on that change alone and another 5 mph by changing from a 62.5 jet to a 49. finally, check the timing (something i haven't yet done and don't really know how, though i know it's important). hope that helps.

RE: performance carb problems

I've got a 20mm Keihin on my ped and I'm doing 50 Mph with only 49cc's. Before this carb I had a 16mm and before that a 12mm.

You need to precisely calibrate the carburettor by setting the airscrew to the right position, then checking if you need a larger or smaller main jet, then adjust the needle height and then resetting the airscrew to the correct position. If you do this correctly your bike will run great. Check the color of the sparkplug to see if the engine is running lean or rich.

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