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my friend has got a Mac allister. Push mower with a Briggs and Stratton 500 series
Engine. 158 cc. Eng number. 12 1206 51 11580
He brought it second hand. It would start but was running rough and had black
Smoke coming out of the exhaust.
So i removed the carburettor and cleaned it out and changed the diaphragm
And gasket.
Now it starts ok and runs on full throttle ok but the idle is rough and
Popping.
I done a compression test and got a reading of 70 psi.

Do a search using this in the forum search box, “Briggs 500 series engine”. You will find it under the magnifying glass in the upper right hand corner. This problem has been seen multiple times and you should be able to find a solution, without us rehashing it again. If you can’t solve the problem come on back and we’ll go through possibly solutions again.

10T502-0111-H1

Boy we all need a push mower engine with 158 hp.

That’s only used by the commercial guys who get paid by the job.

Check for vacuum leaks. Spray carb cleaner around carb mount and any intake pipes. If it smooths out you have a vacuum leak.

slomo