# Tecumseh HM80 - Dies after 10 minutes



## ts8169 (Nov 9, 2015)

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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## cranman (Jan 23, 2016)

sounds like a bad coil to me.....


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## vinnycom (Nov 6, 2017)

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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## Ian Ariens 924 (Dec 22, 2015)

cranman said:


> 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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## ST1100A (Feb 7, 2015)

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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## ts8169 (Nov 9, 2015)

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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## Snowbelt_subie (Dec 20, 2016)

ts8169 said:


> 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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## ELaw (Feb 4, 2015)

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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## Jackmels (Feb 18, 2013)

I'll bet the Fuel Cap isn't Venting. Drill a Small Hole in it, and see what Happens. 









Climate Change is a Hoax by Globalists


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## ELaw (Feb 4, 2015)

He did say he tried loosening the gas cap...


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## ts8169 (Nov 9, 2015)

Yes, I both loosened the gas cap and ran the engine with no gas cap. Wasn't the issue.

Machine has a plastic gas tank, not metal. Doesn't mean there isn't a clog there. 

I do not have an inline spark tester, but they look pretty cheap to buy ($5-10). It's a real good idea.


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## vinnycom (Nov 6, 2017)

spark or fuel?
when its about to die spray some carb/brake clener into carb intake and see if it keeps it going, if yes then spark and valves are good(imo), then its a fuel delivery problem.
check bowl fuel level when it dies, if it has fuel then delivery is good and issue is w/carb.
adjust fuel air mix screw as it could be set too lean(hot muffler), donyboy has a vid on adjusting that or some hole is plugged up like the air vent hole which is often overlooked.
spark tester would help in see if it looses spark while its running


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## Fat City (Feb 11, 2017)

Sounds like the gas cap is not venting . Try running with cap off when it dies . Most Tecumsehs have a 3/4" female hole tapped into exhaust port . Use a screw in muffler .


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## uberT (Dec 29, 2013)

My vote is for the electronics. I had an identical issue with a TORO. It was the ignition system.


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## 2.137269 (Nov 15, 2019)

bolt on muffler re thread the holes and install heli coils, as to the fuel issue inside the carb the seat for the needle is a tiny rubber insert into the carb body,i have seen then inlarge and cut of fuel flow, even if the carb is a few years old,the residue left after running them dry for store age ,the left over ethanol turns into what looks like beige saw dust in the carb and clogs up the works, again it's something i've seen a lot ,customer plays safe runs it our of fuel,what left over dries up,fresh gas causes the junk to plug up the jets and passages 
also fuel lines swell up inside from the E reducing fuel flow to the carb


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## markopollo (Nov 30, 2019)

sounds like a coil issue to me, 

the float on the carb could also be stiff and not fully going down, (thats why when you hit the primer it saves it self a little bit)
the needle and seat could have some dirt in there (with the bowl removed, see if the fuel flow is good, should be a nice smooth line of fuel)

but my money is on a bad coil. (the blue flame might be the coil trying to restart again, burning the exhaust gases)


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## CarlB (Jan 2, 2011)

ts8169 said:


> 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?



sounds like exhaust valve clearance is too tight


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## ts8169 (Nov 9, 2015)

*UPDATE* 

Just had the carb rebuilt and despite the carb being fairly new (start of the 3rd season I believe) the float was set really low....from the factory? For Tecumseh's, I guess they're supposed to be set slightly higher than level whereas mine was far below level (I could have this backwards). 

Had some other work done, all professionally as I just don't have the time to do it myself these days. Waiting for the next significant snow to see how things turn out.


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## greggmischenko (Dec 12, 2017)

ts8169 said:


> *UPDATE*
> 
> Just had the carb rebuilt and despite the carb being fairly new (start of the 3rd season I believe) the float was set really low....from the factory? For Tecumseh's, I guess they're supposed to be set slightly higher than level whereas mine was far below level (I could have this backwards).
> 
> Had some other work done, all professionally as I just don't have the time to do it myself these days. Waiting for the next significant snow to see how things turn out.


Did you inspect coil/ignition system? I had very similar running issues/symptoms on my older HM80 with condenser/points ignition system. After cleaning/adjusting the old carb multiple times and even putting on a brand new OEM carb I had the same problems. As soon as I replaced the points/condenser it runs like a dream!


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## tdipaul (Jul 11, 2015)

.

so far you've had the following items thrown at you:

bad coil, 

carb adjustments, 

fauly vent cap, 

tight valves, 

clogged petcock strainer, 

stiff float needle, 

dirty float needle, 

points/condenser 

Which is basically everything. 

If the machine was running good last season but now it is not, first check I'd do is under the shroud to see if there is a mouse nest in it and causing the engine to overheat. Its free and easy to do. 

Then check all the other things


*
Whatever this ends up being please post it so everyone learns something*


.


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## gibbs296 (Jun 22, 2014)

Predators are $99 at HF right now, probably less hassle in the long run.


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## ST1100A (Feb 7, 2015)

it does sound like a heat related issue, that's why I mentioned valve clearance, and like another mentioned, get an inline spark tester and see if you loose spark when the engine dies out to rule out a bad coil or other ignition related components.
He tried it with the fuel cap off to eliminate a blocked vent. Another thing to check besides the fuel valve screen is the rubber fuel line itself, they can become clogged or swell internally and you wouldn't notice it from the outside.
Some of those fuel lines were tucked in to the cooling fins behind the flywheel and there is the possibility of the gas boiling in the hose causing a "Vapor Lock" condition, then it would act as it is running out of gas and the spark plug would be dry and he would have spark.
Just a few ideas to check, hopefully you can get it straightened out.


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## badbmwbrad (Jul 30, 2019)

Check your valve tappet clearance; especially the exhaust valve. It appears that your engine cold starts OK but has difficulty operating as it warms up. Thermal expansion causes a warmed exhaust valve to be _longer_ than a cool exhaust valve. 

In addition, unleaded fuel does not coat the exhaust valve seat with lead. There is no "cushioning effect" otherwise provided by a coating of lead. 
During operation, the exhaust valve disc slams into the un-coated valve seat. Any high point on the machined exhaust valve disc and/or seat absorbs the majority of the impact energy when the valve disc makes contact. A micro-weld occurs at the point of impact and when the valve re-opens, a microscopic piece of the exhaust valve seat (at the point of impact) is pulled off the valve seat and shot out the exhaust. 

Multiply this event millions of times... causing the exhaust valve disc to recede (sit deeper) as the seat is gradually removed. The result is the clearance needed between the exhaust valve stem and the lifter closes up. When the engine is hot, the exhaust valve is not fully closing causing a loss of compression.

Check the engine compression when it's cold then again when it's hot. Check the exhaust valve clearance by removing the carburetor and the valve cover located behind the carburetor. If the clearance is too small, then remove the cylinder head and remove the exhaust valve (a simple lever can be used to compress the valve spring to release the split ring valve keeper. Carefully grind away some of the valve stem. Use the same lever and a pair of plastic tie-wraps to compress/hold the valve spring during re-installation of the split rings. Use a wire cutter to cut the tie-wraps.


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## ts8169 (Nov 9, 2015)

*UPDATE*

We received about 4" of sticky snow yesterday and she's running pretty good after the service. I ran the machine last night and after 20-30 minutes there were no issues to report. Because it was dark out, I did notice some glowing orange deep inside the muffler, but that was all. The muffler is now properly bolted. 

I'm almost certain the culprit here was the carburetor float being set too low, which is surprising given it was nearly new carb and I never mucked with the thing. Dying issues could have also been due to the hot exhaust gasses heating up the carb & gas in the carb (broken muffler).


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