QuestionI have a Murray 20" lawnmower with a 4 HP Briggs and Stratton motor. It was running fine the last time I used it when all of a sudden the engine speed started to swing from almost stalling up to normal. I cleaned the air filter, put in new gas and sprayed everything I could with carb. cleaner. This engine does not have a throttle control but there is some linkage underneath the air filter that is swinging back and forth as the engine speed changes. There are two springs attached to the linkage and they both appear to be OK. Nothing looks loose or disconnected.
The engine oil was clean last week and now looks like it is getting darker. Probably because the motor is running so rough.
I have had the motor about two years but because my yard is so small I probably have used the mower less than 20 hours total time.
What do you suggest?
AnswerThis is a classic "dirty carburetor" problem. The repair is not that difficult, but often requires an air compressor to clean the carburetor.
When a mower enters this shop with this symptom we remove, disasseble and clean the carburetor with compressed air and carburetor cleaner. This fixes 99.9% of engine reving problems. Once in a while we find a defective spring, but this is very rare.
You may want to try just using some spray carburetor cleaner to clean the carburetor but the compressed air ensures that you get all the small carburetor orfices clean.
Let me know if you have any other questions.
Eric
