Re: starter won't stay ingaged
weak starter , weak battery or both. I was getting that often in the bitter cold of winter.... the motor starts to fire...I am guessing the flywheel over comes the starters gears push and forces the gear back down, but ther wasnt enough MOMENTUM to sustain firing.
you could also be missing spark in one or more holes. make sure the motor is primed correctly....
there may be another reason, but your symptoms were the same as mine and I explained how i over came my issues.
hope it works for you
bob