Back firing is most likely caused by the ignition timing being retarded. What do you mean by "Blowby?
I think you mean lots of blue smoke from the tail pipes?
If that is the case then with so few miles on the engine I would suspect some worn valve guides caused by burning unleaded fuel in an older leaded fuel engine.
Provide some more details if you have not solved your problem.
Wednesday, April 15th, 2009 AT 4:01 AM