15.5 Briggs runs bad

Bob S. · Jul 26, 2014

I have a Sears mower with a 15.5 OHV engine. It ran good for the past 10 years, was hard to start the past month or so, starter drag. It just started running bad and backfiring through the exhaust last week. I adjusted the valves (rocker arms) to .004, it stopped backfiring but wont rev up and sounds like it"s not breathing right.
Any help would be appreciated, the grass is getting pretty tall.
Thanks,
Bob

Steve@Advance · Jul 26, 2014

Did you replace the spark plug? They can look fine and do some strange things, like cost a lot of money chasing another problem! BTDT! LOL

Is the governor linkage as it should be? Throttle opening fully?

Does partially choking the carb make a difference? If it brings up the RPM, it's too lean. Trash or water in the carb, vacuum leak.

How does the spark look? Try easing the plug wire loose while it's running. Should be able to pull it away from the plug a 1/4 inch or so before it misfires.

joe csuti · Jul 26, 2014

Might want to do a leakdown test on eng,many of the older mod 14-16hp ohv have a history of being hard on head gaskets as they tend to leak/blowout between the valves.

joe csuti · Jul 26, 2014

When you set valve clearance was piston 1/4" into it's downward travel AFTER TDC?

If you set valve's with piston AT TDC this might be your problem as valve tappet may not have been clear of acr cam.

Bob S. · Jul 27, 2014

I didn"t know about the 1/4" ATDC trick, I will give it a try.
Thanks for the tip.
Bob

15.5 Briggs runs bad

Bob S.

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Steve@Advance

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joe csuti

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joe csuti

Well-known Member

Bob S.

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