RPM's fluctuate on B&S engine.

Old 05-22-16, 10:28 AM
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RPM's fluctuate on B&S engine.

I have a 42A707 Briggs and Stratton 17 hp twin engine. When I start it it is hunting and surging at low RPM's. I give it more throttle and it seems to go away. I start to mow and usually after about 5 minutes it dies and won't start until it cools down. I have replaced the fuel lines, fuel filter, cleaned the carburetor, inspected and cleaned all the hoses and air filter and it still has the problem.

Any suggestions?
Old 05-22-16, 01:40 PM
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While it is idling try spray/dribble some carb/brake parts cleaner behind the carb and around the intakes mating surfaces, if the engine tempo changes you have an air leak of some type, maybe a failing gasket or cracked intake. Have a good one. Geo
Old 05-22-16, 02:21 PM
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The problem with it dying is probably the coil. Those engines are notorious for coil problems. When they heat up, the spark will die and the engine shuts down, then as it cools, it begins to work again. Check for spark immediately after it dies to know for sure.

The surging might be cured with a carb adjustment. Under the air filter at the bottom of the carb in the very front of the engine is a screw if your carburetor is an older version. If not, there will be a welch plug there. If it has the screw, just back it out 1/4 turn or so and the surging will rpobably be gone. If it has the plug, you'll need to take the top off the carb and clean it out and blow out the passages.

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