No start when hot-Tecumseh 10hp HM100

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rubberchicken

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I have a 2004 Powermate Generator with a Tecumseh 10 hp HM100 engine. When engine is cold, it starts on the first or second pull. When hot it refuses to start. Replaced spark plug, ran cold and hot compression tests which were almost identical at 82 psi, no change. Carb was just rebuilt. If the engine is running and I hit the ignition off button, I can relight the engine if it still has a few rpm left by turning on the ignition button. Checking for spark- the spark seems absent or weak if I check it when warm, but as it cools off I can get a reasonable spark. When I put the plug back in after detecting the spark, it will start up and run fine until next shutdown. It is not a vapor lock issue- I kept suspecting further carb problems after my first run in with dirt in the jets. So I tried putting an ice pack on the carb as soon as I shut it down, but that did not help either.

I am convinced its some ignition problem, but I am wondering if I am missing something. Am I on the right track to suspect the ignition / coil ?
 
Originally Posted by WhyMe
i have the same engineon my gen and shredder. when warm they always needed to be choked to restart .

In this case the amount of choke has been test countless time without starting. But once the engine cools down, it starts fine.
 
1. Valve recession, valve clearance.
2. Head gasket, loose head bolts.
I don't think that it is the coil but you should check for spark when the engine is hot before looking at anything else.
 
Originally Posted by AandPDan
Weak or absent spark when hot means coil. It's a common failure.



That is where I would look.

Is there any other sources that could kill ignition like a low oil level switch that could be faulty?
 
As others have said, it is most certainly a bad coil if you have weak or no spark when hot. I am assuming it is electronic ignition.
 
It does sound like the ignition module. (Tecumseh calls it an "Lamination")

First, if it has a low oil shut off switch, unplug and retest. It's a single wire connection.

If issue is the same, no spark or weak spark compare to cold spark test. I would highly suspect the ignition module.

What happens is after running for about 15 minutes to get engine to operating temperature, when engine is shut off the cooling fan is no longer blowing cool air across the ignition module (first) and cylinder cooling fins (second).
Then the ignition module gets heat soaked (could be seconds to a few minutes) from the hot cylinder it's mounted to. If the ignition module is "iffy", one of the two windings or electronic connections sealed inside expands and becomes disconnected. Now we have no or weak spark. Cooling allows reconnection, then spark.
 
I was thinking the coil just from the title. I still agree with the others. Your testing for spark when hot (no/weak spark when hot) would further suggest the coil as the issue.
 
Originally Posted by old1
As others have said, it is most certainly a bad coil if you have weak or no spark when hot. I am assuming it is electronic ignition.

Yes, a 2004 Tecumseh engine has an electronic ignition module.
 
Been struggling with a Coleman 5kw powered by a very balky HM100. I bought it when we were kid-less. So thats at least 37 yrs. Loaned it to nephew to build BIL's house. Has slowly declined in performance since. Makes electricity Just the engine is very iffy. Last time it ran, it went for 20 minutes before it died. Please post a follow up.
 
Andyd- the HM100 engine has been around for a while. This unit was purchased in 2004 and came direct from the distributor , so I assume it was built in 2003 or 2004. On yours, you might have points ignition.

Regarding valve recession- this is one of the things I was looking at, mentioned in a number of other sources. One test is to run a cold and hot compression test. If the engine actually starts when cold, then check hot compression readings and see if its lower. In my case the readings are identical at 82 psi. I thought 82 was really low but other sources consider it fine. I would estimate the engine has about 40-50 hours on it. Based on what I see so far, I tend to rule out valve recession, but a valve clearance check is needed to fully rule it out. Given that the ignition kit is about $15 I might try that first.
 
Very interesting finding !! I had time and went out and tested it over the last 2 hours: I disconnected the low oil shutoff at the coil, and now it seems to start fine when hot. The oil level is fine, so I am baffled why it would shutdown due to that switch. I ran it under load for 10 minutes, then shut it down and restarted many times. It worked fine
smile.gif
I wish it was the ignition coil- that part seems to be much easier to replace.
 
Do you really want to replace the low oil level s/d switch? IMO, I'd just leave it unplugged.
 
Originally Posted by JTK
Do you really want to replace the low oil level s/d switch? IMO, I'd just leave it unplugged.


If its inexpensive then I would like to replace it. I rarely use the generator, but when I do its for 12-48 hrs continuous due to power failures. So far I have been unable to figure out the part number. I am going to test it some more to make sure that is really the issue.
 
== SOLVED == Tecumseh 10 hp HM100 engine in generator, will not start when engine is warmed up.

Disconnected, then reconnected, the low oil sensor wire. Repeated a few times. Verified that the low oil sensor is causing the problem, so I left it disconnected for now and it runs perfect.
 
I'm happy for you, Rubberchicken. Alas, my HM100 doan have no stinking low oil shut off to fail. It has an CD coil ignition. In my advanced stage of decrepitude, I am physically incapable of pulling the recoil hard enough. I was trying to use a smaller fly wheel wth a ring gear. A righteous electric start fly wheel and starter is too much money, Better just to cut losses. Thing is loud. A shame because the 5 KW generator worked great. I had it powering 2 dryer coils cherry red to test it after I popped the breakers on it.
grin2.gif
 
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