Engine hunting

[Jack B.]

Could someone please list the causes for engine hunting? This seems to be a real problem that I see a lot of. But aren't there multiple causes. Hit and miss cures can be very time consuming.

[Azis]

It is hard to state a common cause for so many different engine types but I can tell you some that I have ran accross and read of in manuals.
Usually I find the fuel/air mixture is not set correctly.(A lean mixture can be a cause) On carbs that are adjustable, the factory recomended setting is a starting point and usually will have it close enuff but each engine is a bit different and each will usually have a sweet spot just off the initial setting. Surging at low speeds can be solved alot of the time by simply increasing the idle speed. A number of things can effect fuel/air mixture, leaks or blockage be it to air or fuel.
Another common cause I have seen is the linkage and springs for the carb/govenor either being installed incorrectly(some just modified during the installation most likely due to incorrect installation procedure, hence a need to bend or modify)
The govenor is the component that is responsible for maintaining a constant RPM as the load on the engine changes, however at least in my findings, the govenor itself is usually not the problem.
Page 26 of this manual http://www.cpdonline.com/692509.pdf gives some theory and checks for govenor suspected problems. It is for Tecumseh but the theory can be applied to most other small engines as well with similar govenors.

[puey61]

What application is the engine on?

[Jack B.]

What application is the engine on?

It's off of a sears walk/behind lawn mower with an engine no. of 143.996004 which crosses to a LEV 115 tecumseh. It has a governer that I've never ran into before. The governor seems to be "pushed " onto the governor shaft and held in position by spring steel. It has the governor lever held by a screw off to the side. The part that's pushed onto the shaft seems loose. It's really hard to tell because the shaft doesn't turn much.

[cheese]

Hunting is alost always caused by a lean fuel ratio (partially clogged or misadjusted carb or air leak).