Tecumseh Hmsk80 needs full chocke to run.. - Snowblower Forum : Snow Blower Forums
 
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post #1 of 5 Old 02-11-2015, 04:23 PM Thread Starter
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Angry Tecumseh Hmsk80 needs full chocke to run..

My Tecumseh Hmsk80 needs full chocke to run, muffler turns red and engine will only run at low rpm even with full throttle.

Is it the exhaust valve?
Having problems to get new head gasket to this engine in norway also
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post #2 of 5 Old 02-11-2015, 04:24 PM
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I would say either exhaust valve is leaking or it is running lean. Might just need the carb cleaned. Also check for an intake leak.

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post #3 of 5 Old 02-11-2015, 04:27 PM Thread Starter
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Tried to run engine, it first started easy and for the next 10 minutes rpm's gets lower an lower. (Only with full chocke)
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post #4 of 5 Old 02-11-2015, 09:56 PM
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Quote:
Originally Posted by HS80 View Post
My Tecumseh Hmsk80 needs full chocke to run, muffler turns red and engine will only run at low rpm even with full throttle.

Is it the exhaust valve?
Having problems to get new head gasket to this engine in norway also
Did low compression #'s prompt you to get a new head gasket & consider valve issues?

You may be able to salvage the old metal head gasket by cleaning it & the mating surfaces then spraying with permatex copper gasket spray if available in Norway.

Pull the valve cover / breather to check your valve clearance by measuring the maximum clearance using a feeler gauge (min of 0.008"). When doing this, there's a good chance that you'll tear-up the breather gaskets so make sure you have 2 on-hand before performing this check.

Good luck!


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post #5 of 5 Old 02-12-2015, 11:39 AM
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Let the additives do their thing..

Just last night, I just managed to resolve a surging issue on my HM80, not exactly the same problem you have, but I think that one or all of the following will either fix your problem, or at least help you get there:
(1) Guarantee a clean carb, (get a new one!).
(2) Slightly enrich the idle-mixture.
(3) Keep working the additives.
You are running lean: Closing the choke simply prevents more air from getting in, which would make the mixture too lean to run at all. The lean condition could be caused by either the idle-mixture, or a stuck valve. But a dirty carb has been ruled out, because you have (or will) replace it, RIGHT?
And I understand your issue of parts availability, but even a clean carb requires a rebuild kit.
Easiest way to clean a carburetor is to replace it. How can you go wrong for US$25 ?. I started there. New carb made no difference. So I added 3 oz Marvel Mystery Oil to the oil, and 1 oz to the gas tank, and 1 oz into the cylinder. cycle the crank a few times and let it sit there for several hours (a bunch will come pouring out the carb throat, so be sure to catch it!). Put the spark plug back in and start it up. It will blow black smoke for a a few minutes. Run for ½ hour, and then replace the spark plug. At least that is what I did, it is called ‘engine decarb’ and is better described here
I also put 2-4 oz of Sea-Foam in each gas tank refill. Ran for about 8 hours total (generally 2 hours per operating cycle). 2-1/2 blizzards in the Boston Area have helped to add up the engine cycles, for sure.

Finally I changed the spark plug (again), enriched the idle-mixture by ¾ turn, and added a heavier dose of Sea-Foam 2 oz of Sea Foam to a ¼ full tank.
Chugged a bit at first, then it took off with full smooth RPM and no surging. It could have been the idle mixture, because the motor was doing fine when the auger/bucket was full of snow to throw out. Was it due to one or all of those final 3 tweaks? I doubt it. I think it was regular treatment of the SeaFoam. I will try to undo the mixture and spark plug, at some point. Since you are running at painfully slow idle, the additives will be limited in how much they can really do.
Again, I have to point out that my symptom was not the same as yours: but the idle-mixture has an effect on two of the three major modes of operation: low-idle and so-called fast idle (‘full throttle’ but no load on engine). The third mode is of course the ‘doing real work part’ (engine under full load: auger engaged, throwing snow), where so much fuel is being forced up the main jet, that the smaller passages/ports of the idle circuits are of little influence.

next, as I’m sure you’ve been advised, would be the check the flywheel key and pull the head to service/check the valves.

Here is another great youtube video showing how to check/clean the valves without pulling the head:
Free a STUCK VALVE without removing head
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