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Why can a small carburetor cause and engine to overheat?

I understand why lean jetting and things like that can cause overheating, but why can an improperly sized carb on the small side cause overheating issues? I read that the volume of mixture in the cylinder shouldn't change in the cylinder, so that kinda kills my theory that you are simply increasing the amount of mixture for added cooling... although that may be negated by the extra power and heat from burning more mixture. Anyone know for sure?

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A carburettor is chosen by the volume of the venturi on it. A small carburettor will not be able to supply a rich enough mixture. Evaporating gasoline, just like alcohol rubbed on your skin, takes out heat as it turns to vapour (that's evaporative cooling). If there isn't enough gasoline evaporating in the engine, the engine overheats. So, choose a carburettor that is at least big enough for the engine it feeds. As engine displacement is fixed, what changes is the amount of gas the carburettor can feed, hence, a small carburettor supplies a too little volume of a too lean mix.

Posted on Mar 11, 2009

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