Hi!
If your electric starter cannot turn the engine over you have a too weak battery or a too weak starter!
Use a 10A 12V Motor cycle battery or...a 14,8V ,2000mAh LiPo battery (I use both ).

If you have the engine in the plane ...just leave it there and run a couple of tanks full at fairly fast rpm,if you don't know what that means get help from a fekllow club member that does!
Use a 10x6 APC prop, OS 8 or Enya 3 or 4 glow plug and rew the engine at around 12000-13000rpm (you don't need a tach , just listening to it). Always set the rpm with the high speed needle when running it in ...not with the tthrottle! That way you always know that the engine gets enough fuel and does not run lean...provided you can hear when it runs lean...or run rich!
It' vital when you learn how to set an engine that you learn to set it by ear! That's the fastest way and most exact way of adjusting an engine. Do not! I repeat! Do not rely on just how much smoke the engine belches out! It's not an exact way of meassuring how.
rich the engine is running. And pinching the fuel line is also an inferior metod of setting engines.

Second! You must use silencer pressure and have the tank mounted according to the tank mounting rule. That's very important!!!
The tank size is also important! A 240cc (8oz) tank is what you should use for your 6,5cc (.40 ) engine.