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Briggs runs rough at full throttle


aspeltz1

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OK guys,

The Briggs 300421 engine in my B10 just started to misfire something fierce. It idles ok but at full throttle the engine shakes, misfires, sputters, and eventually stalls. Removed carb, disassembled, cleaned everything especially main jet, and reassembled. No change. Any ideas?

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Blow back on fuel line for starts and see if that helps. If it does you probably have crud in the fuel tank. You'd be surprised how many fines sneak in the tank when re-filling.

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Somehow this year I have spiders in my one fuel tank}:) It was capped too.

Also check with an ignition tester(inline kind) for any coinciding spark miss issues. Sometimes a breakup can be indicated by that, either coil or plug.

Valve lash clearances can limit performance as well if it it does not perform well when warmed up but better cold. Currently fixing that on my B112.

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Doubt it's the carb...my old auto shop teacher, who was one smart guy, told use that 90% of carb trouble is ignition! For the most part he was right. I would give it a good tune up one item at a time and see if that helps. Could be just a bad plug. I've had them spark just fine laying on top of the head but under compression will not fire. That paticular set of plugs got flung far into the weeds!!

Harry

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Thanks. New fuel line and fuel filter. Tank was cleaned a few months ago prior to painting. Same issue. I'll start with the plug.

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I'd still check for fuel flow, then you got that one put behind you . Fill up a pint container with gas and if you have a solid flow move on.

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You stated you replaced the fuel filter, what did you replace it with. If you didn't use a filter designed for small engines that would be the cause of your problem.

Rick.......

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quote:Originally posted by dentwizz

Also check with an ignition tester(inline kind) for any coinciding spark miss issues. Sometimes a breakup can be indicated by that, either coil or plug.


id="quote">
id="quote">Briggs sells an excellent inline spark tester (works well in daylight also), $16.
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