I would investigate the cold start system now. It sounds like it is not functioning as it is what increases the fuel mixture for starting as opposed to changing the mixture screw. Check the wiring and see if there is voltage to the cold start valve when the engine is cold during cranking. Look for broken wires, disconnected plugs etc but it could be a bad thermo-time switch. Refer to D:04:06 in the workshop manual. David Teitelbaum vin 10757 --- In dmcnews@xxxx, "Rustproof" <Rustproof@xxxx> wrote: > Thanks guys for your input! (David, Andy and Bruce) I took your advice and > investigated all of your suggestions. Through the process of elimination, I > have been able to solve the excessive combustion problem ...it seems