Tecumseh 5hp lacks power when warm

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threeputtpar

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Aug 4, 2011
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Appleton, WI
Hey fellas -

I've got a small problem with the snowblower that I could use some help with. It runs well when it's first started, but after about 15-20 minutes of blowing snow it seems to lack power when under load. After 30 minutes, it really won't throw the snow over the front auger anymore.

This is a rescue machine that I've gone through and cleaned and serviced everything. At first I tried an emissions carb and it ran well for the first two times I used it. The third time, it started to develop the problem of lack of power. I ordered a new adjustable carb and installed that and tonight was the first time using it again. I'm a bit stumped as to what can be going on. The first time I fired this thing up after it sat for years, it was very strong. It seems that each time I use it, it's performance degrades.

Might this be an ignition problem? It got a new plug (J17LM) for the maiden voyage. Can the ignition be tested at all? Will heat cause the coil/magneto/solid state to not deliver a proper amount of volts and weaken the spark? Flywheel key maybe a bit sheared and the timing is off?

It's a HS50 67292J for reference on Partstree.

Thanks.
 
To test the magneto when it is hot and acting up: Disconnect the plug wire and hold the bare metal end 1/4" away from the head and pull the motor over by hand. If the spark is blue it should be good. If it is orange or yellow it is too weak to produce reliable power.

Sounds like you have got the complicated stuff covered. Maybe it is something simple? How is the oil level? Maybe it is fixing to seize from oil starvation when it is warmed up and cold ambient temperatures are preventing it from doing so.
 
How's the valve clearance?

If good, have you checked for mouse nests, etc, under the cowl? It does sound like it might be overheating.
 
Went out to finish up the driveway and it has low power even when cold. Pulled the plug and with it hooked to the wire and grounded on the head, the spark jumps the gap but it's yellowish and not very bright in a dark garage. It doesn't click like I remember a good spark does.

I also noticed that a small part of the exposed section of the muffler is slightly glowing orange.

Is my ignition not 100%? Should I start by pulling the shroud and checking the magnets on the flywheel? Just replace the coil?

Thanks again.
 
Originally Posted By: threeputtpar
...... the spark jumps the gap but it's yellowish and not very bright in a dark garage. It doesn't click like I remember a good spark does.

I also noticed that a small part of the exposed section of the muffler is slightly glowing orange.


Almost sounds like a sheared or shearing flywheel key. Starting to retard the timing and causing late ignition.
 
Take the muffler off and look for carbon buildup. Also make sure the exhaust ports are clear. You may even want to remove the emissions device in the muffler...if there is one.
 
Originally Posted By: Propflux01
Originally Posted By: threeputtpar
...... the spark jumps the gap but it's yellowish and not very bright in a dark garage. It doesn't click like I remember a good spark does.

I also noticed that a small part of the exposed section of the muffler is slightly glowing orange.


Almost sounds like a sheared or shearing flywheel key. Starting to retard the timing and causing late ignition.


Does that mean pulling the flywheel to get visual conformation? I was hoping that it wouldn't end up being that.

Would a key starting to shear make it run good and then in the middle of a pass up the drive it would lose power and not get it back?
 
My solution to a weak HS50 was to go to Harbor Freight and shell out $99 for a Chonda motor. It bolted right up to my old Simplicity and has tons more power.
 
Possibly a leaking exhaust valve. That would cause the muffler to glow. I had a neighbor that had the same issue with a 5hp Tech. I removed a few thousands from the stem of the exhaust valve. This also reduced the compression release on the ex valve, which gave it more power. Blows snow just fine now. This requires removing the cylinder head and valves. The only way to check the flywheel key is to remove the flywheel. Even a partially sheared key can cause issues. It is difficult to see a partially sheared key with the flywheel on.
 
Originally Posted By: Dean85
Possibly a leaking exhaust valve. That would cause the muffler to glow. I had a neighbor that had the same issue with a 5hp Tech. I removed a few thousands from the stem of the exhaust valve. This also reduced the compression release on the ex valve, which gave it more power. Blows snow just fine now. This requires removing the cylinder head and valves. The only way to check the flywheel key is to remove the flywheel. Even a partially sheared key can cause issues. It is difficult to see a partially sheared key with the flywheel on.


This. If it is glowing then you have some sort of timing issue or an exhaust valve that is leaking.
 
89$ HF motor is probably cheaper than fixing and 6.5hp.

unless thats the one with the goofy dual rotating shafts.
 
Last edited:
Yep, it's the one with the dual opposite rotating shafts.

I really took on this machine as a project and a reason to spend some time out in the garage, but I've since sold my newer snow chucker so this has become a priority.

I'll be pulling the flywheel as soon as I have time and replacing the key, whether it's damaged or not. I'll probably take the opportunity to clean up any rust on the flywheel and magnets.
 
I am also trying to fix a tecumseh hssk50 that has low power (stalling when trying to blow snow and not idling well). I found the valves had zero lash (maybe negative lash). I ground the valves to .010" lash and it seems to be fixed. The compression went from 75 psi to 105 psi, but I haven't had snow to test it yet.
 
Quick update from last night's tinkering:

I pulled the pull start housing and inspected the flywheel. The magnets were dirty and rusty along with the corresponding spots on the coil, but I've read that that shouldn't make a difference. The flywheel came off pretty easily, and the key holding it in place looked to be brand new so I didn't replace it. I feel safe in saying that timing is not the issue.

I'll take the coil into the local shop on lunch and see if they have any way of testing it. Either way, from what I saw last night I think a valve adjustment job is in my plans for the weekend. It's been getting harder to start the last couple of times, and when it does start it slowly sputters until it can gain enough momentum to build up the idle. I've read a few other forum posts that had the same symtoms and it comes from lowered compression when the exhaust valve doesn't fully seat closed.

Anyone know off the top of their head if I'll need to remove the intake pipe/carb and the muffler to gain access to the valve cover? It looked like at least the intake would be in the way, but I wasn't sure about the exhaust. It'd be nice to know so I can pick up gaskets when I'm in the shop. Thanks.
 
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Yes you will certainly have to remove the carb/ intake, and will be easier if you do the muffler also. Muffler MAY not have a gasket, but you will need a manifold gasket and head gasket, and a valve cover gasket. Use a file to shorten the valve stems if needed, and I think there should be .010 clearance. While the valves are out, check them to see if they look like they have been leaking. They may need to be ground.
 
I have the same 5hp tecumseh Ariens sno-thro. These old engines last forever if maintained (mine is from 1968). I suspect yours needs a new set of points. Whem installing a new set, set the gap at.022". This allows the rubbing block .002" breakin amount of additional clearence. If its old, it does not have solid state ignition. FWIW

Oldtommy

PS: Send me a PM with the serial # and I can probably tell you the year it was built.
 
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