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post #1 of 8 Old 02-08-2016, 06:18 PM Thread Starter
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HMSK100 Stumbling

Hello, I am new to the forum and would appreciate opinions from those more experienced than me on a Tecumseh HMSK100 that I'm trying to rehab. The engine is on a ~1973 Ariens two-stage Sno-Thro that I picked up for free over the summer. I don't know the maintenance history, or even if this engine is original to the machine, but I know that it is a John Deere badged Tecumseh HMSK100-159182T (D). The engine ran when I got it, but not well. It also had signs of neglect (very grimy/dirty, dirty oil, nearly dry auger gear case, etc.).

Since picking it up, I have installed a brand new carburetor and new spark plug, changed the motor oil and auger gear case oil, replaced the fuel lines and inline filter, and lubricated the throttle linkages. The motor runs decently now (no problems starting up using the electric starter, idles fine) but stumbles as the throttle is increased. I don't know if what I'm seeing is properly called a misfire, but as the throttle lever is increased the engine will almost die, the muffler will cough smoke, and then it will typically recover and get up to full throttle. If the throttle is increased too quickly, the engine can die when it hits the "stumbling" point. If the throttle is raised slowly, it usually recovers and gets to full throttle. I have been using it in this state to clear snow, it works well enough but does make me nervous that it's going to bog down and die in wetter snow (I'm not sure if this is a symptom of whatever is wrong with the engine or just a limitation of the power of this engine, this is the first snow blower of this type that I have owned).

While I've tried to describe the problem in some detail, nothing beats a movie, so I made one. Please see the YouTube link below (look for the stumbling at about the 0:14 and 0:48 second marks):


I have about gotten to the end of my experience with coaxing small engines back to life. I would appreciate any suggestions of where to look next to figure out exactly what is causing this problem and fix it. Thank you!

Last edited by rollerd; 02-08-2016 at 06:21 PM.
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post #2 of 8 Old 02-08-2016, 06:53 PM
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Is that replacement carb fully adjustable? Sounds like it's idling a bit low - but you need to see about getting a bit more fuel in the higher RPM range I think. SO - you are either needing to adjust it with the carb screw - or may need to drill out the jet (or get a bigger jet). I guess it could also be that is has valve trouble - but that should be more consisitant I would think.




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post #3 of 8 Old 02-08-2016, 07:37 PM
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+1. Sounds like a carb that's out of adjustment (lean main &/or rich idle would be my guess)...hopefully it's adjustable!

L-head service manual; page-16 (20 in the .pdf).


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post #4 of 8 Old 02-08-2016, 08:14 PM
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Since this is an Airens machine, and the engine says John Deere, I would hazard a guess that its not the original engine on there.

Remove the carb cover housing, and take a look at the linkages that connect the throttle lever to the governor arm, and the governor arm to the carb throttle plate. Since you had the carb off, its possible you may have one of the linkage rods in the wrong place. There are several videos on Youtube, showing how these should be set up and which holes the rods go through.

Make sure you find one that shows YOUR carb and throttle. The carb plate and throttle control have several holes and it's important that you get the linkage rods in the right holes for your engine arrangement. Also, make sure that the governor spring hiding behind the throttle lever is not broken, and that it's hooked into the correct area in the slot in the top of the throttle lever which the governor linkage goes to.

Also, check the throttle plate where the linkage goes on top of the carb, and see if the plate has come loose from the shaft and is kind of semi free floating on there. It should not be a problem on a new carb, but if that's the case, Donyboy73 has a video showing how to deal with it. Did you replace the gaskets on the intake when you changed the carb as an air leak there can cause it to run ratty.

Once you are sure all that is right and correct, you can try adjusting the idle up a bit, and then low speed mixture, and high speed jet, if you have those adjustment screws available. Once again, see Youtube for where they are located and what to do.

By the sound of it on your video, the engine is not getting up to the max RPM. It should be around 3600 according to the manual. Yours sounds slow to me. When you had it out blowing snow, did the engine speed stay reasonably consistent with and without snow load, or did it tend to bog down when you got into deep or heavy stuff?

You might also want to check the valve clearance when the weather gets a bit warmer. That needs to be done with the engine cold. Too much slop in the valves will make it run badly, as will valves that are not sealing well. If that machine sat outside for its entire life and was not looked after, it may need a little extra TLC to get it back in top form.

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Last edited by skutflut; 02-08-2016 at 08:20 PM.
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post #5 of 8 Old 02-08-2016, 09:10 PM
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I bought a 1978 ariens with HM80 late last fall and the motor had been neglected. I cleaned the carburetor but plan to do more after winter. When I start it up and don't let it warm up good if I rev it up, it stumbles and has smoke like yours. If I let it warm up good and rev it up slowly its fine. After it gets good and warm no more problem with idle too fast speeds.

I thought yours seemed better, less smoke the second time you throttled up. How does it go after you've run it awhile?

My plan is after winter, I will take mine apart, check the valves clearance, seats, and clean out any carbon deposits with the head off and then if needed tweak the carburetor.
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post #6 of 8 Old 02-09-2016, 05:15 PM Thread Starter
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Thanks so much for the advice everyone, I really appreciate it!

The replacement carb is adjustable. When installing, I made sure to put the governor linkage arm in the same hole as the original carburetor (the plates with the holes appeared to match exactly). And, after installing, I followed the steps laid out in Donyboy73's video on adjusting a carburetor (this one). The fact that several of you think this is the issue has me doubting that I did it correctly though, so I will definitely revisit this.

Skutflut, your comments have given me pause to consider a couple other issues as well. When I installed the new carburetor I replaced the gasket between the intake pipe and the carburetor, but I'm wondering if I should also attempt to remove the intake pipe and replace the gasket between it and the cylinder housing? I also probably need to inspect the governor and throttle linkage in a bit more detail. I tried to clean and lubricate them, but otherwise didn't mess around. I'll also see if I can figure out the RPM on the engine at full throttle.

To answer the questions about performance, when I throw snow the engine stays at a reasonably consistent speed with lighter snow (even a decently deep amount of it). However, it definitely bogs down with heavier end-of-driveway stuff or snow deep enough to reach the top of the auger housing (I just had some of that this morning to deal with). And, the stumbling problem does diminish as the engine gets warm, but doesn't go away.

One final thing I'll throw out there for comment relates to the model number of the new carburetor - and my apologies that it requires a bit of a background. When I picked up the snowblower, the previous owner told me that it was an 8hp engine. One of the first things I did was to clean the machine and spray on a coat of engine paint. I unknowingly painted over the engine info decal and, when I couldn't later find any identifying engine markings (I was looking for engraved numbers in a different place from the decal), proceeded on the information that it was 8hp. When I had difficulty with the original carburetor, I removed it and brought it to a local repair/supply shop. One look at it and they recommended replacement. I started to say that it was from an 8hp Tecumseh and the guy ran from there and got me the new carb that is on the machine now. The new carb is Tecumseh model no. 632334A. Since that time, I discovered my accidental overpainting, cleaned the decal off and learned that the engine is in fact a 10hp HMSK100. The 632334A carburetor appears to be for the HMSK80 and HMSK90 engines, while the recommended carburetor for my specific engine is part no. 632370A. From what I can tell looking at pictures online, there doesn't appear to be any (external) difference in these parts, but I'm wondering if maybe the 632334A carb doesn't deliver enough fuel for the larger 10hp engine? Or am I worried about nothing here?

Thanks again everyone! I'll update with more once I get a chance to act on your advice.
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post #7 of 8 Old 02-09-2016, 05:21 PM
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I believe the primary difference from an 8 to a 10 HP carb is that it would have a slightly bigger jet. I think your looking at lack of fuel more than anything. Watch the vid's about drilling out the Tecumseh jets and i think you will see how to do it.....




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post #8 of 8 Old 02-09-2016, 06:25 PM
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You can further identify you motor. The model and serial no. are stamped into the top of the sheet metal blower housing, maybe hidden under the starter push button unit if you have one. If its rusted/painted a lot you may have to sand down to find it.

Last edited by AL-; 02-09-2016 at 06:31 PM.
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