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Engine Surging


Bob Shepler's Avatar
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07-02-02, 06:28 AM   #1  
Bob Shepler
Tecumseh surging

Tecumseh 12hp OHV engine on Sears Lawn Tractor starts fine. Engine surges to high speed, drops to low speed, surges again, etc. It cycles about every 2 seconds regardless of throttle setting but does kill at idle setting. Carburetor appears clean, linkage is free but governor rod is driving surging. What should I look for?

 
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garywms's Avatar
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07-02-02, 07:41 AM   #2  
Have one just like it. Could be an ajustment needs to be made to the carburator, of it could be the carb has a blockage. Take off the screw that hold the float bowl on. The should be a small hole in the screw. Make sure that it isn't clogged. If it is, then the other tubes in the card are probably clogged. You would need to take off the carb and use a welding tip cleaner to open up the various pickup tubes. But try the carb adjustment first. Mine does that even when the adjustment is right, but smooths out under a load.

 
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07-02-02, 06:39 PM   #3  
Bphillipsz
Fix for surging

You should be able to get rid of the surging by turning the screw on the bottom of the carbeurator bowl slightly. Try 1/8 turn clockwise as viewed from the top. Wait ten seconds or so between adjustments, and you shouldn't turn it more than half a turn. If cw doesn't help, or is worse, try ccw.
Good Luck

 
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07-02-02, 08:20 PM   #4  
Bob Shepler
Thanks for the suggestions. I tried them both.

I took the carburetor apart and cleaned all jets and holes with wires and blew air through them. They were all open, I didn't find any dirt or obstructions. The carburetor looked pretty clean inside. I guess it should, I don't have that many total hours on the engine.

After assembly I tried adjusting the fast idle screw on the bottom of the carburetor bowl. I tried both directions until the engine died. The cyclic surging continued just like before. It surges when under load too.

I'm not sure what to try next. Does anybody have any ideas?

 
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07-02-02, 09:38 PM   #5  
Does your throttle shaft move freely? Check your governor linkage to make sure it isn't bent or loose. The governor may have gotten out of adjustment where the gov. control lever is attatched on the side of the block. It does sound like a carburetor issue though.


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07-03-02, 08:01 AM   #6  
Here's one for you Cheese.

Same engine. When it first tries to start, you get a no compression condition. Open up the OHV cover and find that both of the valves a real loose. Adjust them to the correct specs. Try starting again and the engine revs out of control like the govenor is bad. Here is the kicker. If you open the valve cover agin, the valves have lost the adjustments you just made.

Real head scratcher, ain't it.

 
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07-03-02, 07:07 PM   #7  
Well, {scratching head} Do the adjusters have jam nuts on them, like some older OHV engines, or are they lock nuts? It they are lock nuts, I would replace them. Another possibility is that the steel valve seats may have come loose from the aluminum head, letting them move around enough to make accurate adjustment impossible.


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

God bless!

 
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