Hello. We have a Craftsman 42" riding mower with the B&S 20hp OHV Intek single cylinder (model #31P977 type 0635 E1). This mower is approx 15 yrs old but hoping to get a little more usage. However I am scratching my head and wondering what I could have missed. After it's off season sleep added fresh fuel and it started right away and moved 50 feet to garage to prep for new season. Did notice in that short span it ran at full throttle and would not slow but did not give much thought.
Gave carb side of engine a good clean with carb cleaner and that where problems began. Tried to start again and only result was a very slow rpm that would run 15-20 seconds. I checked fuel flow before and after the fuel cutoff valve and fuel filter there was no clogs. Remembered in past couple seasons at low idle it would have some surging but continued on to check spark.
Cleaned the surface rust off flywheel magnet (only one-correct?) and made sure the magneto had proper gap at flywheel. Did the old school test of viewing plug while turning motor over and there was a visible spark. Put plug back in and attempted restart but there was no improvement.
At this point decided it was time for new parts. I have replaced the carb, magneto and spark plug looking for the culprit. After all this best it will do is maybe a one minute run at the very low rpm and that is not an immediate start.
I am a novice with small engines and at my wits end. Wondering at this point if there might be some interior part failure and thinking perhaps might be time to perform a compression check. Blown head gasket? Any advice would be greatly appreciated.
just thought i'd post your engine information, adjust valves per operators manual, page 5, with engine cold
#3
Oliver Douglas
15 years old, compression test, and or leak down test.
What we do at the shop, is clean the fuel system, then try to start. If no start right to the compression and leak down tests.
Head gaskets blow for a number of reasons. A leak down will tell you if its leaking out the sides of the head gasket, OR you have a valve obstruction. Keeping one open, or cracked, or as silly as carbon build up. Which you can knock out with a hammer.
