Small Engine Has Me Stumped

I have a Coleman 5000W generator with a Tecumseh HM100 10HP engine. I keep gas stored in the tank with Sta-Bil and carb cleaner. The gas was about a year old and is 10% ethanol. Each time I use it I turn off the fuel supply valve and let it stop on its own. It has always fired up on the 1st or 2nd pull and run for hours.

Last week I fired it up and after 15 minutes it just sputtered a few times and stopped. It would not restart until it got cool. The length of time it runs is dependent on how warm the engine is. When warm and it finally does start, it might go 5 more minutes.

Knowing that an engine needs 3 things, air, fuel & spark, Here is what I've done:

Spark:
This symptom has a bad coil written all over it. I've seen it many times. I replaced the coil and made sure the armature air gap is to spec at .125". Traded out spark plug with my mower of the same type. Nice and clean with gag set at .30" per specs. Mowed the lawn.

Air:
Filter is new. Tried with no filter.

Fuel:
Completely drained the older gas and blew out the tank completely dry. Ran carb cleaner through the hoses and replaced the fuel filter. Took off the carb and its as clean as a pin. Carb cleaner blasted through all orifices just fine. The carb is nice and shiny clean. I think the needle pin and seat are fine. I removed the reservoir nut and tank after mounting the carburetor. I opened the fuel valve and fuel tricked in. Lightly raising the float stopped fuel from entering the reservoir. Put in brand new 88 octane corn free fuel in the tank. No ethanol.

Other:
There is a low oil shutoff switch. Oil is to the top.

With engine now cooler it started on 2nd pull and then again after about 10 minutes of running it just quit. What is the possibility of a DOA coil? I'm stumped. What should I try next?

Thanks.

Just thought of one: After it quits I'll pull the plug, ground it out, and see if there is a spark.

 

Maybe the gas is boiling in the carb, but I thought thatonly gave you trouble if you cut off a hot motor and tried to restart it hot. Just an idea

Maybe the float sometimes is sticking

 

Vaporlock?

 

I know you said you cleaned fuel tank and line, but, I had similar thing happen to me. One time I had a small pebble stuck in the fuel line, it would allow enough fuel past to pool in the carb, but wasn't letting enough to keep running at full throttle. The other time was when my gas cap was not venting and carb would pull fuel until it was unable to break the vacuum, then starve for fuel.
I know these aren't exactly the same as your situation, but I'd keep looking at fuel issues. Good luck, it sucks when your small motors have issues.

 

Thanks guys.

It does act like it's starving for fuel just before it quits. You can see the hose inlet down right in the center of the gas cap. I'm going to replace the fuel line since I have some fuel hose laying around. I'll see if there light through the outlet. The cap does breath fine. If the spark turns out good after a shutoff, I might try a carb rebuild kit or a completely new for $79. The generator is worth it and works great when running. Also I feel better having a source of power to run my fridge, freezer, circulation fan on my fireplace, and furnace if there is a natural disaster or long term power outage.

 

Cooling issues caused by a mouse nest? Had that happen on a mower with similar symptoms.

 

Not sure how old the motor is or if it applies to the 10hp motors but on the newer small hp motors they replaced the the adjustment screw on the bottom of the carb with a screw/bolt that has a small pin hole in it. This is the bolt that hold fuel bowl on.
To fix shut gas off or clamp gas line take bolt out and blow out the pin hole with a compressor or similar.
Could be an easy fix, this pin hole gets clogged up on all my small engines just about every year.

 

SOLVED: So an easy try was disconnecting the low oil shutoff switch from the coil. Bingo, it ran for over an hour in 85 degree heat. Doesn't even have the occasional misfire like it did before. Problem solved. A new switch is $46. I'll check the oil every few hours on my own for that price.
I was going to buy the poster with the correct solution a full year's worth of gas but no one got it right. Sucks to be you. (No changes to your post. I have a screenshot saved as proof.) I will offer a heartfelt "thanks" to those that gave suggestions though.

 

Just glad you figured it out! I could have used a years worth of gas though...