QuestionI have as Briggs Model 28M707 13hp on a Sabre. It got harder and harder to start, popping back through carb.
I adjusted the valves per OEM specs. This left the intake valve slightly off the seat during the comp. stroke and still no start. I ended with .012 clearance on the intake to get the valve on its seat. Still no start still back firing through the carb. I cleaned the carb., checked the flywheel key, fresh gas, made sure the valves weren't sticking etc. I know the comp release is built into the cam grind and valve clearance is critical. Any suggestions?
Answer You need to set the valves with the piston 1/4 past top dead center on the stroke when both lifters are not moving, not on the other stroke when one is closing and the other opening.
If you have done so, and the valve stems are not at an equal height
then you may have a loose valve seat, which I have seen them able
to peen back in and recut the seat, etc..
Although Briggs recommend a new head.
The valves should be at .004-.006 on the intake, and .006- .oo8
on the exhaust
