Change the spark plugs, even if they're new. Once plugs get fuel-soaked, it's possible they can leak voltage away down the insulator when under compression pressure without jumping the gap. I've seen it happen several times.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!