Tecumseh HM80 - Dies after 10 minutes - Snowblower Forum : Snow Blower Forums
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post #1 of 24 Old 12-03-2019, 01:39 PM Thread Starter
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Tecumseh HM80 - Dies after 10 minutes

I have an 8HP Tecumseh HM80 (circa 1990) that is dying after about 10 minutes of effort. It's as though I turned the ignition to OFF. Engine will restart after a priming and a few pulls, but then will die after 5 minutes, then 2 minutes....repeat... I seems that as the motor heats up, it dies more frequently, but so far I'm always able to get it restarted.

A few years ago I bought a brand new carb (not ebay...). So the carb is relatively new.
Gas is always treated with Marine Blue Sta-bil and "Star Tron / Star Brite".
Gas is drained from the tank & bowl during storage etc..
Fuel line is only a few years old.
Pulled the main jet and cleaned the passages this morning, all clear.
Engine starts up fine from cold and doesn't like to be choked.
Idle Mixture screw is 1-1/4 turns out.
Main Jet runs okay between 1 and 1-1/2 turns out. Rough at 1-5/8. Rough at 3/4. I set this at 1-1/4 turns and engine ran smooth.
I've tried loosening gas cap, but this doesn't seem to work.
I've tried adjusting the main jet when engine starts to struggle under load, but this doesn't seem to work.

I'm grasping at straws here. Muffler Bolt holes in engine block are getting stripped, so muffler not tight = Hot exhaust kinda spewing in different directions between muffler and engine block. Could this be heating up the carb and causing problems?
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post #2 of 24 Old 12-03-2019, 02:26 PM
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sounds like a bad coil to me.....
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post #3 of 24 Old 12-03-2019, 02:29 PM
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do the air fuel adjustments on warm engine. if it starts with no choke its probably set too rich.
fix the muffler. completely remove gas cap to test. check valves, fuel lines, fuel shutoff, needle valve and float

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post #4 of 24 Old 12-03-2019, 02:42 PM
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Quote:
Originally Posted by cranman View Post
sounds like a bad coil to me.....

I agree with cranman, I bet the coil gets warm, quits working.
Seen it a few times.

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post #5 of 24 Old 12-03-2019, 03:18 PM
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Check your valve clearance, sounds like you have tight valves, more likely the intake causing loss of compression and not sealing, you could also have a tight or bad exhaust valve doing the same thing on an old engine, its very common.
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post #6 of 24 Old 12-04-2019, 09:48 AM Thread Starter
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UPDATE: Ran the blower again last night and she ran strong for about 10-minutes. Started right up, did not surge and was blowing snow good. I did have some blue flames at the exhaust / muffler (visible due to night). Not a red hot muffler, just blue flames. Then the blower quit after 10, same symptoms, kept getting it re-started, kept dying. Gas cap fully removed did nothing. Then I tried hitting the primer bulb when the motor started to quit. It worked 2 times / 2 presses of the primer bulb, where the motor "came back" very briefly but there was no real saving it. I think gas even came out of the bulb?

So with the primer bulb "working", I guess this means I have a fuel delivery issue and need the whole fuel system cleaned. So much for stabilizer and draining the carb every spring.... Given age, I'm not sure I want to get into paying someone to pull the head and do the valves at this point, but we'll see. New coil is probably no big deal if needed. Maybe 50-bucks?
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post #7 of 24 Old 12-04-2019, 09:59 AM
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Quote:
Originally Posted by ts8169 View Post
UPDATE: Ran the blower again last night and she ran strong for about 10-minutes. Started right up, did not surge and was blowing snow good. I did have some blue flames at the exhaust / muffler (visible due to night). Not a red hot muffler, just blue flames. Then the blower quit after 10, same symptoms, kept getting it re-started, kept dying. Gas cap fully removed did nothing. Then I tried hitting the primer bulb when the motor started to quit. It worked 2 times / 2 presses of the primer bulb, where the motor "came back" very briefly but there was no real saving it. I think gas even came out of the bulb?

So with the primer bulb "working", I guess this means I have a fuel delivery issue and need the whole fuel system cleaned. So much for stabilizer and draining the carb every spring.... Given age, I'm not sure I want to get into paying someone to pull the head and do the valves at this point, but we'll see. New coil is probably no big deal if needed. Maybe 50-bucks?
do you have an inline spark tester? maybe you could put it on and start the engine. as soon as it dies pull it over and see if it has spark. if not than that is your issue. if it does than it might be some weird fueling issue where it doesn't fill the carb bowl fast enough to supply the engine.

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post #8 of 24 Old 12-04-2019, 10:02 AM
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Does the engine have a metal fuel tank?

The metal-tanked ones usually had a shutoff valve screwed into the bottom that had a strainer on it (inside the tank) - if that's what you have the strainer may be clogged.

It's super-easy to check... just drain the tank then unscrew the valve from the tank.

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post #9 of 24 Old 12-04-2019, 10:16 AM
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I'll bet the Fuel Cap isn't Venting. Drill a Small Hole in it, and see what Happens.









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post #10 of 24 Old 12-04-2019, 10:29 AM
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He did say he tried loosening the gas cap...

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