# engine rpm contantly fluctuates



## nottelybill (Oct 27, 2008)

I have two lamn trimmers, both relatively new. The engines on both of them cycles up and down when in nutral and if in gear they usually die when the rpm level goes down. They go from idle speed to high speed and back. Like your car if you just sat there and mashed the gas pedal and let off constantly.


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## justin3 (Apr 10, 2007)

Engine RPM surging is caused by a lean running condition or a problem with the governor adjustment. Please give us the make and model of the engine(s) so we can have an idea of what we are looking at.


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## nottelybill (Oct 27, 2008)

model 91212 type 0619A
model 92202 type 1242E1
both Briggs and Straton - one of these engines started the problem after the third use.
Is the governor the little blade that swings back and forth that has a wire connected to the carb.? These engines have changed their caburation mechanisms since I use to work on them.


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## justin3 (Apr 10, 2007)

In this case, I do not believe the governor would cause your problem, your probably lies in the carburetor. You have an obstruction somewhere in your carb preventing gas flow or an air leak in between your carb and tank causing a lean burning condition. Your best bet would be to remove the carburator and clean it out and rebuild it using a kit from briggs and stratton.


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## paulr44 (Oct 14, 2008)

Without looking up the carburetor types, many of briggs carbs. for lawnmowers are very cheap. The style screwed right to the tank, like the old pulsa-jets, are about $22.00 - hardly worth messing with!
Paul


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## oscaryu1 (Mar 25, 2007)

I've heard this method works for air leaks: Spray some type of fluid (carb cleaner? something?) at the carburetor. If it starts to raise RPM, then you've found your leak.


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## nottelybill (Oct 27, 2008)

if it were an air leak wouldn't that be constant and not cause a servere rpm level change back and forth? If gas flow was constant and the air leak would simple lean the mixure out to a degree where it had no power or just wouldn't run, seems to me. Also as new as these engines are should I expect to have to rebuild carb every 4 or 5 uses? If so maybe I should just fix them and sell them.


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## justin3 (Apr 10, 2007)

The reason your engine keeps surging is because your governor keeps adjusting the throttle so that the engine will stay running. When the engine begins to die, the governor will open the throttle all the way and the engine will rev up, then when the governor tries to maintain the engines set speed it will begin to stall again and start the process all over again causing surging. 
If your rebuilding your carburetor after every 4-5 uses you have a problem with your fuel, fuel container or dirt in your tank. I have seen people complain of carburetor problems and find out they were using an old metal storage tank that was beginning to deteriorate inside.


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## nottelybill (Oct 27, 2008)

ok, that makes sense. I have all plastic fuel containers and use the same one on all my small engines so I will do a rebuild and see what happens -thanks


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## paulr44 (Oct 14, 2008)

oscaryu1 said:


> I've heard this method works for air leaks: Spray some type of fluid (carb cleaner? something?) at the carburetor. If it starts to raise RPM, then you've found your leak.


Some carb. cleaners will cause the engine to drop RPM or stall. If RPM changes, either way....


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