Hey everybody. I have this Troy built tiller with a 1970's Briggs and Stratton 8HP engine; that will not run. It has gas,spark and compression. It backfires out of the carb. The valves are fine. The carb. was cleaned and rebuilt. I was thinking maybe the carb is adjusted wrong??? Was wondering what you guys thought?
A little history will be helpful. ....What was done to the engine recently? ....When was it last run? ....Was the engine apart?
If you have adjusted the carb to its initial settings (1-1/2 turns from closed on high & low speed needles), it should be close enough for the engine to start. ...Final adjustments are made while the engine is running.
Backfiring thru the carb indicates incorrect ignition timing (wrong coil gap, or partially sheared flywheel key), incorrect valve timing (sticking intake valve, insufficient intake valve clearance, incorrect valve timing, or intake valve not seating properly). ....What makes you say, "the valves are fine?"
In order to backfire thru the carb, the ignition is firing while the intake valve is partially open.