# small engine surging



## MELOC (Sep 26, 2005)

i found a used 5 hp engine for my tiller. it seems to run generally ok, but it does seem to surge a whole bunch. it runs a bit smoother under a load (when tilling). 

the only info i have is that the guy did something to the carb (replaced something i missed as i was gabbing to a friend) i think he mentioned a pump, but i assume he replaced the diaphram? i do have a few gas leaks i can't quite put my finger on just yet. a small plate on the side of the carb gets wet when running. maybe that is where he did what he did? i tightened the screws a bit, but they weren't real loose...they were just under tightened IMHO. it still gets wet even after i tightened them. the other side of the carb is wet too. it appears there is a hole between two of the screws that hold the carb on the gas tank. it appears too small to be a mounting bolt missing...i am unsure without tearing things apart. i was just wondering if these leaks could cause the surging...i just think it is a seperate issue, but i want to hear your thoughts.

the other issue was the dirty valve i saw when i pulled the plug. i saw lots of black in there. could the surging be an issue with the valves maybe hanging or sticking?


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## brewswain (Dec 31, 2006)

surging is commonly caused by a restricted air filter.
clean it
its a too lean condition which may be solved by backing the adjusting needle out


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## TNHermit (Jul 14, 2005)

I got a 5hp troy bilt that does the same thing. it seems to make its own water soemhow. Anyway a little carb cleaner and dry gas in the tank and it clears up. Myabe its from setting out all night and some kind of condensation.


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## Rocky Fields (Jan 24, 2007)

Hey.

Sounds like a possible governor problem.

More info: http://www.smallenginesuppliers.com/shop/html/governor_adjustment.html

RF


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## Blu3duk (Jun 2, 2002)

ANd it could be sucking air around the gasket to the carb.... my walk behind lawnmower had issues I removed the bowl to drain the water, and rust but the gasket swelled and it sucked air, would not run worth sour owl crap, new gasket and it runs smooth as the day off the showroom floor.... perhaps the holes in the fuel line are allowing just enough air into the mix to keep the thing surging like a governor problem.

William
Idaho


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## raymilosh (Jan 12, 2005)

I'd check for a vacuum leak, too. the fact that it does it at idle and not under load definately points to a vacuum leak. The air that gets in leans out the mixture, then the engine slows, the governer opens the throttle plate, allowing in more fuel, the engine surges, but then gets lean due to the air leak, whick decreases the engine speed..and round and round.

test for an air leak by spraying something flammable around the carb gaskets (ether, carb cleaner, etc). If there is a vacuum leak, the engine will pull in the flammable substance, which will increase the engine speed momentarily. That way you can pinpoint the source of the problem.
Have fun with your diagnosis.
ray


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