Lots of Question About Tecumseh HM100-159079H:repairs,upgrades,swaps

I'm hoping I'll get lucky and someone who is expert on this engine and possible upgrades to it will see this posting.

The engine in my Sears snowblower from 1983 is a Tecumseh HM100-159079H that has a breaker point ignition. The snowblower probably has fewer than 100 hours of use even though I've had it a long time because I use my snowplow and only keep the snowblower as a backup.

But, over time, the engine ran worse and worse and became harder and harder to start. Now, it won't even start.

Here is what I've done so far to diagnose & repair it. Please tell me if you recommend that I do something that I may have missed.

Bought a cheap Chinese carburetor for $10, installed it, unit ran even worse. Put back original carb. Insides of original carb looked clean. Only part I did not remove was the emulsion tube since it seemed to require a lot of force and I was afraid I might break it. The carb is getting gas and when I press the primer, I see gas coming out of the carb. I did notice one tiny hole in the outside case of the carb that looked clogged that I am guessing is to let outside air inside and I cleaned it out. Inside of gas tank is also clean. I did have the unit running a few months ago and I adjusted the fuel/air mixture and any other adjusting screws to where the engine ran the smoothest.

I took off the flywheel and looked inside. Things are pretty clean, but I intend to unscrew all electrical connectors such as the wires from the coils that are screwed down to the stator assembly and the bolts that hold on the stator assembly(being careful not to rotate the stator which would throw off the timing) and file them down so they are shiny.

As best I could, I already set the breaker point gap using a feeler gauge to the recommended 20 one thousands. I did this as best I could. It is hard to be certain at what point I might be setting the gap too small and be forcing it open when I slide in the feeler gauge versus when the points are simply snug up against the feeler gauge and therefore not too far open. I did not rotate the stator unit and so the timing is still where it had been. The points did not look pitted or mis-shapen.

Because they are cheap and easy to replace, I'm ordering a new ignition output coil and spark plug wire and spark plug and capacitor and will install those.

When I have the connections from the two magneto coils unscrewed to clean them, I will use an electrical continuity meter to ensure the coils are not open circuited.

Do you think I am making a mistake by not working on the timing? I didn't work on the timing because it seems I would have to take off the head, buy a run-out gauge and magnetic base, and then have to install a new head gasket and put everything back together. I made the assumption that if I ensure the point gap was at or close to 20 one thousandths, the timing would remain close enough to its proper value so as not to be a problem.

I intend to use the compression gauge I use on my car engines, assuming it will fit, and check the compression.

What should the compression minimum value be? About 140 psi just like in cars?

The magnets still all seem to be glued onto the flywheel-none are missing. They totally wrap around the inside of the flywheel with equal gaps between each. If I remember right, there are 6 of those magnets.

The above is as far as I can go with trying to diagnose/repair this. So, again, please chime in if you think I should do something else or do something differently than I did or plan to do.

Next topic: upgrade ignition to solid state????

Did tecumseh make a newer version of this engine or another engine with a solid state ignition that would fit my engine and work right in my engine and if so, can I buy the parts and replace my breaker point ignition with them including replacing the flywheel along with its magnets so that everything will fit my engine and work right??

Last topic: Is there an engine from another manufacturer that I can buy that is not discontinued and has a solid state ignition that can be dropped into my machine with little to no modifications needed? My engine bolts to the mounting surface with 4 bolts. 2 bolts are bolted into the front of the engine to hold on a metal plate that supports the output drive pulleys. I don't care if I also have to buy another output pulley or two to fit the new engine's crankshaft just so long as I can mate them up ok. I don't mind if I have to replace the drive belts with belts that are shorter or longer than what is there now. I would want a complete engine including gas tank, governor, recoil starter(and electric start too would be fine), carburetor, muffler, etc. if available rather than having to buy a lot of individual parts and put them together.

If you are an expert on any of this, please give me your advice. I've already used Google and some other sources and have simply not found much specific information. If you know of any sources you think I missed, please point me to them. Thanks.

Thanks to everyone who posted here or contacted me. I was going to remove the muffler if the engine didn't run after I tried everything else but I forgot to put that step in the procedures that I planned to do-thanks for reminding me of that.
 
Someone else suggested I remove the spark plug after trying to start the engine to see if fuel got into the cylinder. That sounds like a good idea and I plan to also do that.
 
I have an air compressor and an air wrench and I will try rotating the flywheel fast using it by placing the air wrench with a socket onto the flywheel nut. If that rotates the flywheel faster than I can do by pulling the start cord, maybe I will see a better spark going across the plug gap while I have the plug outside the machine and have the plug connected to ground where it should be.
 
There is a video on YouTube of someone whose machine has what looks to my eye to be the identical stator/ignition assembly that is in my machine and you can see that video here if you wish: https://www.youtube.com/watch?v=ZfHJOMzGvdc&list=LL&index=2&t=1268s
 
At runtime 0:34, you get a pretty clear view of my ignition system. The engine is a 10HP just like mine and may very well be the same engine I have.
 
I haven't found a way to post & upload photos. The system here asks for a URL but I don't have a URL for my photos, I want to upload them to this site. If I missed something, someone please help me out on how to upload photos. If I can upload photos, I'll do that.

Thanks for your suggestions.
 
Yes, I have tried using starter fluid, but the engine never really fired, just a backfire or two.
 
When I used the starter cord, I did see a spark at the gap of the spark plug when I had the plug outside the machine, but with the spark wire connected to it and I had the threaded part of the plug grounded to the chassis using a jumper cable. The spark did not look as strong as sparks using the same setup on my cars. I will try cranking the engine with my air compressor using an air wrench which ought to make it crank much faster than I can do by hand with the starting cord and should also keep it going as long as I want so I can get a better look at the spark.
 
I haven't  yet tried measuring the compression. I hope my compression gauge has whatever adapters are needed to fit the spark plug hole.
 
Here is some more information: the inside of the flywheel is continuously lined with magnets all the way around with small gaps in between the magnets. There are 6 magnets and 6 gaps. From what I've read, I assume the magnets alternate in the direction their magnetic fields point.
 
I'm going to try to do as much work on the ignition system as makes sense unless I measure the compression and find it to be way, way too low. It seems I can work on the ignition system fairly easily and cheaply with parts being available online for not a lot of money and that is why I will start with it if the compression is ok.
 
If I change out the ignition coil, plug wire, and plug and capacitor and cleanup all connections including those that are screwed down to the stator plate and also the bolts that hold the stator plate to the chassis and the stator plate itself where it touches those bolts and any other electrical connections to it and I also remove the muffler and the engine still does not run, then I guess all that's left is the carburetor.
 
I don't know what to do about getting the emulsion tube out without breaking it or distorting it badly.
 
I'll try to test the compression in the next few days.

I measured the compression. I don't have an electric starter motor and so I had to do it by pulling the starter rope of the recoil starter by hand. I have not  yet tried putting oil inside the cylinder to see if the compression goes up. I measured 45PSI which seems to be a big problem.
 
I hope within the next few days to post photos on the website suggested above so you can see what my engine looks like.

I did forget to be sure the throttle & choke were open so I ran the compression test again being sure those were wide open and the compression increased from 45 psi to 55 psi, still really low.
 
One thing I noticed was if I threaded my compression gauge in all the way into the spark plug hole, I got zero compression. I discovered that the gauge was actually bottoming out and touching an internal baffle in the engine and if I unscrewed the gauge out of the spark plug hole a turn or two, I again got a non zero compression reading. This happens because the spark plug hole is offset away from the piston.
 
I took off the head and saw nothing obviously wrong and when I manually rotated the engine, the valves opened & closed at what seemed like approximately the correct times during the cycle.
 
The head gasket looked fine and almost new in fact even though 38 years old.
 
There seems to be a cover plate I can take off just under the valves. I'm guessing there may be some adjustments there to the valves that I can make.
 
What, if anything, should I try to do in terms of adjusting/measuring the valve actions and to find out what the reason is for the low compression?

Thanks SRTsFZ6.
 
Here is what I found regarding being able to rotate valves when they are supposed to be closed.
 
Both valves can't be rotated when they are supposed to be closed with the following exception. When the piston comes up from bdc on the compression stroke, quickly after that the intake valve closes. When the intake valve has closed, suddenly I can rotate the exhaust valve and I can continue to rotate the exhaust valve while the piston goes up but when the piston comes very close to tdc, but not quite at tdc, I can no longer rotate the exhaust valve.
 
It appears that when a valve lifter lifts a valve off of its seated position, the valve can be rotated and so I am guessing that the reason I can rotate the exhaust valve when it is supposed to be closed is that the lifter underneath came up very slightly-just enough to slightly lift the valve off its seat. I can further guess that the cause of that might be a bent camshaft and/or some sort of camshaft bearing problem.
 
Let me add another piece of information I neglected to mention earlier that might be relevant. The flywheel key was recently broken off and I got a new one and replaced the broken one.
 
Do you think I should now try to open up the engine(only surface of the engine I haven't yet seen since engine is still mounted to snowblower is its bottom surface and so I assume there must be an engine access cover on the bottom that I will have to remove) and examine the camshaft, camshaft bearings, and other internals? Can you think of any other causes that would cause this unwanted exhaust valve rotation?
 
Thanks again for all your tips, they are right on the money and have helped a lot.
 
Audioresearch

As that cam isn't available anymore, I did find a used one on E-Bay  (Craftsman 8HP Tecumseh Engine Camshaft part #34143).  There aren't any separate cam shaft bearings, just the engine block it resides in.
 
It does indeed have a mechanical compression release...  
 
Even with a compression release, compression should be more than 50 PSI. 
 
I think a failed compression release would make pulling over compression higher. 
All you would need to inspect the innerds is a side cover gasket which is still available.
 
 
 
 
 
 

Valve clearances are measured under the crankcase vent cover, usually behind the carb.
 
If adjustment is needed (too tight), the valve gets removed and the tip slightly ground down until the correct clearance is obtained..