Hi All
I know it is a stupid question, but how to stop the engine when it is required, not waiting for the fuel to run out??

Thanks

I usually also block up the exhaust. Threads like this on other RC forums decend into anarchy!

The generally accepted ways are;

1. Block exhaust pipe, effectively choking the engine up with the exhaust gasses. Most people do this, but some don't like the added back pressure that doing this induces into the engine or the fact that you effectively get left with tons of unburnt fuel in the engine which is never a good idea and could make the next start-up problematic. Ive never had an issue with it however and is my chosen method.

2. Pinch fuel line starving it of fuel, but also lubricant, so this is bad.

3. Block the air intake so the fuel cannot ignite. As the air volume decreases the stoichiometric ratio is wrong so the fuel cannot ignite,. but this is kinda impractical to do and removing the air filter to do this risks your engine ingesting debris and ruining it.

4. Stop the flywheel. Generally regarded the best way, and the one all of the professional & club level racers use, but difficult and dangerous as the flywheel is going pretty fast. It is said that as long as the engine is at idle its perfectly safe and if not try using a gloved hand or your foot. Benefits are that it doesn't stave the engine of fuel, lubricant or oxygen or choke it up with hot exhaust gasses so is probably the safest for the engine, if not your fingers. Again however there is an argument that the abrupt stop causes a large load on the engine, especially the little pins that are on either end of the conrod attaching to the piston and crankshaft.

So yeah, there's not a universally 100% agreed upon way of doing it, so go with whatever your comfortable with to be honest!

Oh, and remember to manually move the flywheel afterwards to its BDC position (bottom dead centre) so the piston and liner can contract back to their cold size without getting squashed together. Its best to make a mark on the flywheel or somewhere like that with a sharpie or a hand grinder to just remove the black colour from it so you know where BDC is, that way you don't have to stare down the glow plug hole and guess every time :)