When cold the motor takes a long time to fire up. I've been turning it over for around 20sec with a 60sec break (don't want to o/heat the starter) and takes 6 or so goes to fire up. Once its warm there's no probs. Engine has had a piston overhaul and i'm running the mixture slightly richer than 50:1 but there is no sign of spark plug fouling. What can i do to get that 'first start' perfomance.