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Tecumseh 10HP HM100 engine hard to start


sjc1701's Avatar
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12-15-15, 08:20 AM   #1  
Tecumseh 10HP HM100 engine hard to start

I have the HM100 159402P engine in a Powermate 5000 genset. It's maybe 20 years old now but has very low running hours. It's always been hard to start (10 or 15+ pulls), only way I've lived with it was to remove the plug and put a little gas into the piston and then start it. It has always performed well when loaded but does require just a bit of choke to keep it from surging at no load (no adjustments on this carb).

I've checked the carb (5165 series) float and it may be just a hair higher than spec but I'd think that should help and not hurt the starting problem. I'm getting to old now to do all the screwing around to get this thing to run, so I'm looking for recommendations;

1. Replace the carb and hope that helps?
2. By a flywheel with a ring gear and add a starter?
3. Put some 'mechanic in bottle' in the gas and run it for awhile to see if that helps somehow?

Since it's been hard to start since day one I wonder if anyone has one of these engines that actually starts easily.

 
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12-15-15, 09:23 AM   #2  
Might check and make sure the choke valve is closing all the way. Also the shaft for the choke and or butterfly could be leaking slightly.
As for the surging under no load, I find this somewhat common in applications such as generators, pressure washers and tillers. As long as they perform under load, I don't worry much about it especially since no load condition is not often or very long in these applications.
My reasoning is in these applications, the load is usually constant and rather large compared to a lawnmower, so the governor is doing as it should which is apply throttle for high torque/load. When in no load it still attempts to do so but then catches itself to prevent over speed.
If a lean condition is suspect, check the spark plug. As long as it is not white or light grey, the mixture should be fine.

 
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12-15-15, 11:02 AM   #3  
The plug looks fine, no indication of to lean or to rich. Like I mentioned, it runs fine under load. The problem is getting the darn thing to start. Should mention that the choke butterfly has a rather significant (at least in my mind) opening in the butterfly itself... day on factory thing. The choke to operate fully from open to closed position.


Last edited by sjc1701; 12-15-15 at 11:05 AM. Reason: Added comment
 
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12-15-15, 11:13 AM   #4  
Which butterfly?
The choke butterfly should close completely over the throat of the carb, if not there may be an adjustment or other reason for it not closing like a restriction...
If you can cup/choke the carb with your hand and see if it starts up, then that would point toward the choke valve/butterfly not operating properly.

 
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12-15-15, 01:37 PM   #5  
The choke butterfly does move to close over the carb throat. Factory design of the butterfly plate has a rather large U shaped cut out so the amount of air drawn through the intake can't be cut out completely. I can't try cup choking the carb since this is a pull start and it takes a might good tug to spin the engine over.

 
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12-15-15, 02:11 PM   #6  
Again, it does not take much to make a difference in my experience. I realize the cutouts are there and for a purpose, never the less, if the valve does not seat in can INDEED make the difference. Especially if there is and adjustment such as the throttle needs to be completely advanced to engage the choke.
Perhaps have some one pull the start while you manually choke the carb?

 
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12-29-15, 01:24 PM   #7  
Thanks BFHFixit. Gave trying to figure it out and bought a new carb through Amazon (for $15 why not). Replaced the plug, new fuel lines and filter, fresh gas and the new carb.... Fired up on the first pull!! I did notice that the choke plate on the new carb doesn't have the extra hole in it like the old one, maybe that made all the difference. Now I have a new head scratcher that I'm gonna post in a new thread, fuel from the tank doesn't want to keep up with the engine when it's at 1/2 rated load. I think it may be running a bit rich but I don't think it should be gobbling up that much gas.

 
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