mardi 23 juin 2015

B&S 6.75 Sputter/Misfire Diagnosis

New to the forum and pretty much confused about my mower. I have a craftsman mower with a B&S 6.75 L-Head engine on it. Over the last year or two it's developed a sort of sputtering problem. It isn't losing much power, but there's a noticeable miss every now and then. Sometimes a few in a row.

So far I've: Replaced and gapped the plug to .030, changed the oil, pulled the carb off and rebuilt it. I should note that there wasn't any junk in the carb but I did replace a broken gasket between it and the air filter housing. I replaced the bowl gasket, bottom nut gasket, and o-ring where the carb attaches to the cylinder. I also replaced the float pin, needle and seat. I ran a pin through all the jets and hit them with quite a lot of carb cleaner. When I put it back together there wasn't a bit of improvement. I've also added seafoam to the fuel tank with other additives over time.

I'm beginning to wonder if it's a valve problem or timing issue that's affecting the spark. I'm thinking of pulling the flywheel to inspect the key. The key was replaced several years ago after an unfortunate incident with a tree stump. It ran fine after the replacement however. The mower doesn't use any oil. I pulled the head and the valves appeared to be functioning fine, but that was just a visual inspection. I also re-torqued the head bolts to ensure I wasn't losing any compression.

I'm at a loss now, any help would be appreciated. I'm thinking of pulling the flywheel this afternoon for an inspection. I'll report back with what I find.


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