Some Diesel fuel in the gas will cause exactly the symptoms you're describing, but the exhaust gas will smell like it's coming from a turbo shop heater. The odor is really obnoxious! Also check the timing mark on the balancer against true TDC of the #1 piston- - - - -balancer rings have been known to slip on the hub.
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!