One more thing, while I think of it. New valves seldom EVER seat perfectly, no matter how well they are lapped. Of course, the secret to having a running engine is to get them to seal "enough" that the engine will start and run. Now the thing is, with brass valve cages and steel valves, once the engine begins to fire, the force created by combustion will force the valves into the seats to a point where eventually they will seal, perfectly. If you have an engine that "wants to start", and everything is adjusted properly to the point where the engine will fire but not "light off on it's own" or starts but only runs very briefly, this is what I do. Hook up the battery and confirm that you have spark occurring at the right time. Fill the gas tank and make sure that you have the needle valve open about two turns, and if you have a throttle, set it about 1/4 of the way open. Bolt or clamp the engine down to your workbench and drive it with an electric motor. Make sure that everything is lubricated well, and let it run.--The main proviso here is that the motor must be firing when it is being driven. After about 10 or 15 minutes of this, as long as the engine is firing, the valves will begin to seal better and better, until they seal well enough for the engine to run on it's own. Of course you can dick around with the needle valve while the engine is being driven until you reach the point at where the engine is firing most consistently. Likewise with the ignition timing if you have adjustable ignition timing. This trick has saved me from insanity two or three times when I had done everything correctly and the engines still refused to start.---And--ALWAYS have a fire extinguisher close to where you are trying to start the engine.
