ORIGINAL: opjose

Yes the needles control the amount of fuel that flows into the carb.

Yes a "too rich" setting will cause the engine to stall in the air. This is why tuning is so important.

Usually people set their engines properly on the ground, but forget that the engine will lean out in flight, so the engine cuts out and they do not know why.

You must run the engine slightly rich to prevent this.


Testing the engine nose up and nose down with 1/2 a tank helps to get the tuning right.

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Hydro lock

Fuel is not compressible.

Get too much fuel in the cylinder head, and the engine CANNOT turn over.

This is called Hydro lock.

If you force it you may break the crankshaft or piston rod... normally the latter.

Hydrolock can occur because of siphoning or user error... you over primed it.

You must drain the excess fuel out of the cylinder head when this happens.

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A cline regulator is used to maintain a constant pressure to the carb under most attitudes.

While normally not needed, it's a nice thing to have, particularly if your fuel tubing is long for any reason.

Short tubing runs increase available flow, so you are advised to keep your fuel tubes as short as possible ( with certain exceptions ).