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Have Craftsman rider with a Briggs 15.5 engine. Have tried 8 different combos for adjusting the valves to try and get it to run correctly, still backfires thru carb. Any sugestions?:frown:

Cabalo said:

Have Craftsman rider with a Briggs 15.5 engine. Have tried 8 different combos for adjusting the valves to try and get it to run correctly, still backfires thru carb. Any sugestions?:frown:

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It looks as if 8 valve adjustment combos would do it because one would think at least one of those 8 were right, especially if the piston was about a 1/4" past top dead center on a compression stroke and you set them at about .004" for the intake and about .006" - .007" for the exhaust.

Another reason, but not with a warm fuzzy feeling, is a valve seat loose or the valve stem sticking in the guide and not getting fully closed in a timely manner. A burned valve is a possibility but rather uncommon compared to the other possibilities mentioned. A sheared flywheel key could be suspect but that often advances timing so far they won't run at all but don't rule it out completely.

OK I've pulled head, checked the seats, valves not sticking, burnt, or other wise damaged. And yes your valve setting was also used. Pulled, cleaned and rebuilt tthe carb, new plug, reset air gap on magneto and just about everything else I could think of. And still it won't run worth a hoot. What else?

Cabalo said:

OK I've pulled head, checked the seats, valves not sticking, burnt, or other wise damaged. And yes your valve setting was also used. Pulled, cleaned and rebuilt tthe carb, new plug, reset air gap on magneto and just about everything else I could think of. And still it won't run worth a hoot. What else?

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Lean fuel or timing is all else I can think of at the moment.

I suppose a vacuum leak shouldn't be ruled out completely either. On some, crank case breather / vacuum hoses can leak and cause a lean condition but idle rpm is usually worse than higher speeds because of greater vacuum at lower speeds.