carbs suck

if an engine has more air and it bogs at low speed but four strokes at high speeds(too much gas) is it posible to have to jet down with more air? could too much gas casue it to bog too? could too little gas cause it to four stroke at top end? well thanks for the info... oh and by the way i cant do any plug chops casue my leg is broken so id like to get this thing running right b4 it heals

Re: carbs suck

Ron Brown /


Unless you can find a test pilot to do some plug chops and other tests for you, you are wasting time.

Having said that, yes, you can be lean at low rpm and rich on top.

A moped carb has no means for providing extra fuel when you snatch the throttle open. You open the carb completely at low rpm, which reduces the vacuum at the needle or atomizer jet, which leans out the mixture. The simplest solution to this problem is to roll on the throttle as the rpms rise. If you are still leaning out when you do this, you need to raise your needle, if you have one, and/or increase the size of your idle jet, if you have one and/or enrich the idle mixture, if you have a mixture screw. You can also get a slide with less cut away but we won't go there.

Before you do any of those things, you have to make sure you have a good, clean air filter, a guaranteed clean carb with no passageways restricted, then do a high speed plug chop. This will allow you to select the correct size main jet. Without the correct main jet, all the other adjustments are meaningless.

The main jet controlls maximum fuel flow, consequently, the slower your engine is turning, the less the effect of the main jet, but it does have an effect down to fairly small throttle openings so get it right then try the low speed stuff.

Good luck on the leg.


Re: carbs suck

this carb worked fine b4 i drilled it out. now after i drilled it it has so much more power. i think i should probably go bigger.

Re: carbs suck

Ron Brown /

"this carb worked fine b4 i drilled it out"

That is a nice little piece of info you left out.

Everything I said still applies, especially the part about the throttle opening being too big to create sufficient vacuum to pull the fuel.

Read my post and think. Drilling it even bigger may not be your best option.


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