Rebuilt Tecumseh HM80 won't start!

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  #1  
Old 02-14-12, 01:36 PM
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Rebuilt Tecumseh HM80 won't start!

I broke the rod in my HM80 on a snowblower. I was able to get a new rod and rebuilt the engine and carburetor. It started after a few pulls and it ran for about 15 mins while I messed with the carb screws and governor. I shut it off and I thought everything was great.

Next day when I went to use it, I was going to fine tune the high and low speed screws and had it running for about 3 mins. when it kept dying at low speed. Then it just won't start any more. I don't get any pop or sound of it kicking over at all now. I tried starting fluid -- nothing. The spark plug is wet and I gapped and cleaned the solid state magneto and flywheel magnet. I can see a spark from the plug wire to the frame and from the wire to the plug when it's installed. Sometimes I get a backfire out of the exhaust. Compression seems OK after I re-torqued the head bolts. There's just no 'pop' or combustion happening when I pull the starter cord over and over, even with starter fluid.

It just seems like maybe a timing issue - that the plug is not firing at the right time? But I'm not clear about why it would run fine for 15 minutes one day, then run OK for 3 mins the next day and slowly just die and then won't start again.

Is it possible that maybe the magneto coil just wore out or got weak in 1 day for some reason? Or maybe the key for the flywheel somehow got loose and the flywheel rotated on the crankshaft? I'm really baffled why it would run one day and then next it doesn't even turn over.

Thanks!
Bryan

Edit: Looking at the HM80 repair manual, I see in the Engine Troubleshooting that I have done most of the things in their list so far. The plug is wet, I tried two different plugs (a new one and the old one that was still working), I installed a new air filter, fresh gas... I guess the next step is to pull the flywheel and see if the key is sheared - and if that's OK, then the coil? Has anyone else gone through this troubleshooting process? Am I missing anything?
 
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  #2  
Old 02-14-12, 03:19 PM
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I think you'll find the problem when you check the flywheel key.
 
  #3  
Old 02-14-12, 05:45 PM
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I think you are exactly right. :-) I pulled the flywheel and guess what was sheared off. hehe

So, maybe greasing the crankshaft and inside of the flywheel was not a good idea? But I did torque the nut to spec (40 ft. lbs). I'm not sure why it would loosen up like that so fast. How many times do you have to torque the flywheel nut before it actually stays torqued?

Thanks!
 
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Old 02-14-12, 06:30 PM
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It doesn't matter if you torqued it since you greased it. You can't grease it. The flywheel key is not designed to hold the flywheel in place during operation, it is just to align it for assembly. It depends on that tight friction fit on the tapered shaft to hold it there. You'll need to use carburetor cleaner or some kind of solvent to get the grease off completely, then reassemble.
 
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Old 02-14-12, 08:01 PM
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Ah... well that makes sense then, thank you! I figured I'd grease it to keep it from rusting to the crankshaft, but I guess that's OK in this case. So... I have 3 keys on order from eBay. I'll have this thing running on the weekend. :-)
 
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