Tecumseh HM100 driving me nuts

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New carb behaves like old carb. Engine starts gets warm, and starts popping back through the muffler.It will die in about 5 minutes If I start it on choke after it dies, it will die when I open the choke. Would a bent fly wheel key do this? Perhaps a stuck valve? The last time I messed with it was 5 yrs ago. If memory serves me, it was acting up then. I'm open to suggestions TIA
 
If a new carb didn't fix it I would check a few things:

-Flywheel key
-Coil/points are producing a good enough/constant spark
-Compression

I've seen a few of these with leaking valves causing issues. Sometimes the valve just isn't seating all the way and needs a little bit ground off the end so it closes.
 
Originally Posted By: andyd
The last time I messed with it was 5 yrs ago.
The gas isn't 5 years old right?
 
to me it sounds like it's either running lean (carb, intake leak) or there's a hot spot in the head. carbon buildup? warped valve? too little valve clearance? might pull the head and have a look....
 
you could test for hot spots by running a tank of premium gas. if that helps, it's a hot spot issue. If it doesn't help, it's probably a mixture/leak issue.
 
Thanks guys.I have a blue spark. Gas is less than a month old. So,the coil is good. I have a fly wheel with a ring gear that I want to use, so I'll do that when I replace the key.
 
Originally Posted By: jeepman3071
If a new carb didn't fix it I would check a few things:

-Flywheel key
-Coil/points are producing a good enough/constant spark
-Compression

I've seen a few of these with leaking valves causing issues. Sometimes the valve just isn't seating all the way and needs a little bit ground off the end so it closes.


+1 I was leaning compression or fuel related. How old is the fuel filter? I have a B&S that would die out when the engine warmed and wouldn't restart. Replaced the generic filter with a smaller one and have had zero issues since.
 
Some of those had a screen in the gas tank that can get clogged and cause fuel starvation. Check and make sure the cap is venting as well.
Could also be flywheel key or valve adjustment.

If it is a newer pointless electronic ignition, I have seen those get bad and start dropping spark as the engine warms up, but work fine cold.
 
Small engines need 3 key ingredients to run:

1. Fuel and air at the correct mixture ratio
2. Spark ignition at the correct time
3. Compression so that the piston pulls a vacuum when it travels downward

Out of those three, which one is the most likely to be a variable ?

Answer: The fuel and air mixture ratio

Carburetors bolt on, but they need adjustments as soon as the engine starts running.

If the carburetor has no provision for adjusting the mixture, then the main jet will need to be drilled larger until the mixture is rich enough for the engine to run smoothly.
 
I just ordered a coil. Despite having a decent spark when shorting out the loose plug, The way the exhaust pops is a rich mixture and a weak spark will cause that. If that doesn't fix it , I will dig further. Though the engine is 35 yrs old, it has less than 100 hrs on it. I think the low hrs would contra-indicate needing a valve grind.
 
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