Techumseh problems


Old 05-30-04, 09:24 PM
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Techumseh problems

Murray Lawn tractor with 12 HP OVXL120 202046D engine.
After mowing for around 1 hour I hit a rock that stopped the blades...I quickly disengaged the blades with the clutch and backed up ...the mower was running verry rough and backfiring...I throtled down and it smoothed out enough that I could limp it over to the barn.
Things I have checked: flywheel key, valve setting .004 for both exhaust and intake...this was given to me as the setting by a local mechanic, but I have seen a lot of different settings for Tech engines...although this setting has worked for the last 2 moths, At TDC the magnet on the flywheel is about one inch past the receptor this about right?
I spin the flywheel and check the spindel below and there is no preceivable wobble to the shaft so i doubt that the crank is bent, but who knows?
Then i removed the bowl from the carb, and although unrelated to the rock... there was water in the gas... so I took the carb apart and thoroughly clarn all parts and re-assembled....I set the air/fuel needle out 1.5 turns and the throttle control to 1 turn...It will start but it has flames out the exhaust and it backfires very bad.What am I missing?
Another question....While I had the flywheel off I noticed two star type allen head adjusters that are under the flywheel in the top of the engine case that run parallel to the top of the case....What are these for?
Any Ideas?
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Old 05-31-04, 12:25 AM
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I would dismiss the possibility of the crankshaft being bent since the blades are belt driven.But I would check the spendles good.blades,belt and deck level.But I'll get into that latter.But now to the problem at hand.You said that"It will start but it has flames out the exhaust and it backfires very bad."That tells me that your engine is out of time.The exhoust valve is open(at lest)part of the time that the spark plug is fireing.Now a flywheel key is designed to brake/shear when a engine is stoped abruptly like that so as not to brake something inside the engine.And it doesn't take much of a dint to thro an engine way out of time.So recheck the flywheel key because something bout the position that you said the magnet was in don't sound right to me.After you do this re-check the valves to see that masurement has changed(that's both valves setting at 0.004 on TDC)
You had water in the float bowl,replace the fuel and fuel filter too.Cause water mite still be in the tank and if it is it will be back in the carb. before long.

Now about leveling the deck.(John Deere makes a nifty tool for this for under $10.00, that's what I now use)it makes it easer.Make sure that all 4 wheels are up to proper PSI.(it's on each wheel)pull mower up on a concrete slab.Let deck height lever down to mid point(2 or 3),rotate blades to point out.measure from bottom of blades to ground on both sides.ajust deck till both blades measure the same.Then rotate blades to point back to front,measure again at front an back.This time the back measurement can be 1/16 to 1/8 lower than front.


Old 05-31-04, 11:38 AM
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Hello Tadpole!

The engine could be out of time, as suggested...but another reason for flames coming out of the exhaust is a lean mixture caused by a restriction in the carburetor (which is a distinct possibility since you found water in it). Did you tighten the flywheel nut really tight? If not, the key may be sheared now. You didn't put oil on the shaft before putting the flywheel on did you? If so, the flywheel key is sheared.
Old 06-01-04, 04:16 AM
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RE: Techumseh problems

The flywheel key is not broken....but the setting of the carb could be a problem...what do you suggest for the needle valve setting and the upper air needle setting? I got the engine to start and run, but it is still rough...I continued to adjust (slowly) the needle valve out with some effect but not significant improvement...The main needle valve is just slightly pitted could this be my problem? It did run fine prior to the rock hit...
I also cleaned the engine of all oil and found that the sump gasket, (below the finned cylinder) is leaking oil....could this loss of vacuum be a possible problem with the smooth running of the engine? Other than splitting the case is it difficult to replace this gasket? While open should I check on anything else? Thanks for the feedback...
Old 06-01-04, 04:38 PM
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Water in a carburetor will give the same symptoms as incorrect ignition timing. The only part related to the timing is the flywheel key. I would recheck the water issue in the bowl by again removing the bowl to inspect. I suspect you will find water again. Furthermore, a complete fuel system flush sounds to be in order, using compressed air. The sump gasket will not affect engine performance (only 2-strokers will, with a bad sump gskt). Nothing to necessarily to check for once inside the engine other than a general inspection and cleaning. The two "star shaped allen head screws" are merely plugs for the oil passages. These passages are machined then sealed at the factory by way of these plugs. The pitted main jet should not cause your trouble although this should be replaced. The proper valve clearances will be .004" on each valve. These need to be set with the piston 1/4" past TDC after the compression stroke (this eliminates the compression release camshaft from coming in to play). The position of the magnets in relation to the coil sounds correct, since any engine is designed to fire before TDC. The fuel adjustment screws are correct at 1 and 1/2 on the main jet and 1 turn out on the idle circuit screw.
Old 06-03-04, 04:56 PM
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Goodday Tadpole

What's the verdict. Anything further to report?

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