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Tecumseh 12.5 hp OHV governor problem


alpineal's Avatar
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03-01-05, 10:36 PM   #1  
alpineal
Tecumseh 12.5 hp OHV governor problem

My Craftsman riding mower is powered by a Tecumseh 12.5 hp OHV engine. Governor hunts between high and low rpms. The governor shaft and linkage work smoothly. Just a couple of seasons on this relatively new engine and it has performed flawlessly. The original carburetor and its new replacement had no effect. Fuel lines cleaned. Fuel filter blown out with air nozzle. Fresh fuel. Carburetor settings per manual have no effect. No amount of tweaking alters the wandering governor. What is next?

 
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03-01-05, 11:24 PM   #2  
tweaking

Hi
You can't tweak a governor adjustment--it has to be right on. That means throttle fully open and shaft turned same direction full--far as it will go when connected with all linkage in place. May have bent some linkage or put in wrong position. Maybe spring in wrong position--maybe spring is streched?? Some of those linkages had to be the correct direction as well because they stuck and caused surging if they were swapped end for end. Hope this helps

S/T

 
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03-02-05, 12:35 AM   #3  
Also, try removing the air filter. If that corrects the problem, replace it.


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

God bless!

 
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03-02-05, 07:51 AM   #4  
Azis
Intake leaks may also be a problem if that is the engine I am thinking of. The intake pipe is higher than the carb.
Just a couple of seasons on this relatively new engine and it has performed flawlessly.
New engine as in, purchased replacement? Overhaul or rebuild?

Here is a digital manual that may help also.
http://www.cpdonline.com/692509.pdf

 
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03-02-05, 09:20 AM   #5  
alpineal
Tecumseh governor

Thanks for your excellent comments.
When I said tweaking I meant no amount of carburetor tweaking.
Removal of air filter had no effect.
New engine was purchased directly from Tecumseh.
I'll check governor linkage to carb for unusual bends/warps.
I'll check for intake leaks.

 
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03-03-05, 08:44 AM   #6  
Azis
Carburetor settings per manual have no effect
If your carb has mixture adjustments, use the manual from the link I provided and adjust the carb per instructions. The initial settings the manual descripes are just that, initial settings. From there it may need adjusting, usually enriching the mixture(CCW) will solve the surging. If it runs normal at full throttle and under a load, and only surges at idle, this would be the first place I would check.

Also beaware that "New" does not always = "Good"

GL

 
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03-08-05, 11:39 AM   #7  
alpineal
Tecumseh governor trouble update

Checked and replaced intake gaskets at both ends.

No warps or bends in linkage from governor to carb.

Replaced carb with new from Tecumseh.

No change.

Held governor shaft while engine running and hunting was reduced. Implies problem inside engine.

Removed engine and lower end housing to expose governor. Governor gear and flyweights are in good condition. Governor rod and its motion are good.

Remove spark plug and rotate crankshaft on stand. Smooth operation. Some hint of bearing noise, but smooth piston movement.

This is a tough one. Thanks for your help.

 
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03-09-05, 06:52 AM   #8  
Azis
Are there mixture adjustments on the new carb?

 
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03-09-05, 10:57 PM   #9  
craftsman problem 12.5 tecumseh

hi
we had some ohv engines with the factory high speed setting too high and it caused what you are describing.. Drop the rpm and you may solve your problem. Adjusting screw on throttle mounting plate. Setting for RPM should be around 3000 -- Sears does not use the 3600 number and suggests 3100 max.

S/T

 
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03-10-05, 12:51 PM   #10  
alpineal
Tecumseh governor problem solved

Thanks again for your help.

The new carb has identical adjustments to the original (both supplied by Tecumseh). Resetting those adjustments and paying attention to the high speed comment got things going smoothly again.

Along the way, here are the anomalies that were corrected:
Intake manifold gasket at head was half gone and was replaced.
Carb was replaced with new Tecumseh.
Discovered flywheel magnet was contacting spark module and readjusted.
Main drive belt found to be on wrong side of keeper at the engine shaft.

Despite all of these problems, I believe that more careful attention to carb adjustments, i.e. finer settings and knowledge of the high speed setting would have put this one to bed earlier.

 
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03-11-05, 06:30 AM   #11  
Azis
I believe that more careful attention to carb adjustments
Good job glad ya got it!

 
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03-11-05, 09:49 AM   #12  
Proper storage procedure is by far the most important area of concern. While todays gasolines aren't the best, it is varnish build-up during storage that is the biggest villian to any carburetor. Be sure to use a quality fuel stabilizer - added at the correct amount, based on the volume in the gas tank - and furthermore, run the engine at least once a month during this time of inactivity. If you prevent varnish, you likely will never have to service your carburetor. Provided though that you replace the fuel filter and air filter(s) as needed, never stretching them out to save money.

 
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