Rumblee

Ive got a 91 GTU. It starts up good, runs for a sec, then dies. It will run if i give it some gas, but it lacks power, and puffs smoke out only one side of the exhaust. I checked for bubbles or spewing of coolant and there was none. It doesnt use any either. I pulled the plugs and it makes a nice rhythmic thumping sound. BUT, the plugs on the back rotor were pretty clean and smelled like gas. The plugs on the front rotor were black and smelled of gas but not nearly as much as the back two. What is this an indication of??? Any help is greatly appreciated.
Thanks,

Drew