# Tecumseh engine idles up and down



## bushkanaka86 (May 13, 2009)

I am working on my mower which has a Tecumseh 640174 engine (model 143.995502). It didn't start at all, so I took the carburetor completely apart and replaced the float and was able to get the mower to start. 

However, while I was able to cut the grass, the whole time it ran the engine continued to rev up to cutting speed and drop down to idle. I could see the throttle butterfly constantly moving back and forth. There is no choke or manual throttle control on this model of mower. 

I read that this probably means the engine is running lean and I need to clean some holes in the carburetor. I ended up completely taking the carburetor apart 3 times and soaking everything down with carburetor cleaner. I made sure the main jet was clear as well as all 3 holes in the bowl bolt. After cleaning it 3 times, I can't find anything else that could be plugged.

The engine still runs but it still does the constant revving. The only solution I found so far was to completely tighten the idle screw so the engine idles at cutting speed. I don't know if this is good for the engine though.

Thanks for any help you can give!


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## AVB (Nov 28, 2014)

LEV 115 - 355016D with 640174 carb.

Do a static governor adjustment first.

Repair manual has the procedure in it.
http://www.mymowerparts.com/pdf/Tec...P-4-CYCLE-L-HEAD-FLAT-HEAD-ENGINES-692509.pdf


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## bushkanaka86 (May 13, 2009)

Thanks for the reply. I will try out the steps in that manual. I also had 2 ideas and I wonder if either of these could cause this result:

1) I didn't notice any brass low speed jet like in the diagram of a similar carburetor on another website. There were no other screws I could take out in the carburetor. I also didn't notice a low speed jet hole in the side of the pedestal but I wasn't looking for that one. I would have seen the brass jet though, I think. 

2) My float was bad and I bought a new one. They didn't have a new metal one for me so I got a plastic one. The new one came with a spring that my metal one didn't have. I installed the spring like it was diagrammed and it provides a constant, low, upward pressure on the float. Could that possibly be causing it?

Could either of these result in the constant revving?


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## bushkanaka86 (May 13, 2009)

I did have another idea. If I hold the solid link between the governor and the throttle, the engine reaches the correct RPMs. The governor appears to be adjusted as much as possible to the full throttle position so I can't adjust it but I am wondering if the governor spring has lost some tension and needs to be replaced.


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## AVB (Nov 28, 2014)

bushkanaka86 said:


> I did have another idea. If I hold the solid link between the governor and the throttle, the engine reaches the correct RPMs. The governor appears to be adjusted as much as possible to the full throttle position so I can't adjust it but I am wondering if the governor spring has lost some tension and needs to be replaced.


That just proves that it is governor related problem and not carb related and that why I suggested doing the static governor adjustment first. It can be spring related but most times it is the static setting does this and not the dynamic one.


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## bushkanaka86 (May 13, 2009)

AVB said:


> That just proves that it is governor related problem and not carb related and that why I suggested doing the static governor adjustment first. It can be spring related but most times it is the static setting does this and not the dynamic one.


Well the only problem is that I can't adjust the static adjustment anymore as far as I can tell. The governor lever is all the way to the left which should be full throttle. That is why I think it is a spring issue.


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## k2skier (Sep 30, 2008)

The carb is lean. If it revs up and down consistently, and it may run and die once or twice on a cold start after priming, the carb is lean. It's called a lean hunt. If it has a plastic main nozzle, it must be removed and both orings need to be changed. The float setting is not level.


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