# Surging/Hunting Tecumseh HM100



## cadblaster (Sep 17, 2005)

I've got a 10 hp tecumseh hm100 horizontal shaft engine on a Sears (american yard products) chipper. I've had it for 8-9 years now. Every time I put it away I close the gas valve and run the fuel out of it. 

I used it recently and it ran, but It's surging/hunting for an rpm. So I removed, and cleaned out the carb (twice now), replaced the plug, the air filter, and tried brand new fuel. The problem actually got worse. If I try to steady the throttle, it'll die out. I did hold the throttle wide open for a few seconds, and it ran up to a high rpm, but also sputtered like it was loosing spark. This occurs with no load on the engine, and with the chipper mill engaged.

It's a constant speed engine/carb (series 3 or 4, I have to check), so it's pretty simple without many adjustments that can be made. I did adjust the float a little, but not much else. It was too low. 

The o-rings on the main and "idle" screws are not in great shape, but it's not leaking so they should be ok. Throttle and choke shafts appear to be tight and in good condition. 

My thought is to check for a weak or intermittant spark. But I'm not sure what's the best way to check this. Weak spark is somewhat subjective, and intermittant may not show up by pulling the rope (no electric start).

Any suggestions would be great, I'm not sure what to try next really.


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## cadblaster (Sep 17, 2005)

Okay, so no one wanted to take the time to read through my long post. 

so I'll keep it simple.

How do I check for a weak or intermittant spark?
Will worn o rings on the carb cause my troubles? even if not leaking.


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## bbnissan (Nov 7, 2004)

> I've got a 10 hp tecumseh hm100 horizontal shaft engine on a Sears (american yard products) chipper. I've had it for 8-9 years now. Every time I put it away I close the gas valve and run the fuel out of it.


I hate to say this, but this will do absolutely nothing to help your piece of equipment. Even when you run "all the fuel out of it", there is still a rather large quanity of fuel left in the bowl of the carb. This fuel will sit and varnish up the jets and passages in the carb and make it run like you are describing.

You need to pull the carb apart and clean it thoroughly. Also make sure you get the very very tiny holes between the treads of the "bolt" that holds the bowl on (there should be 1-3 of them depending on the carb).

In the future, don't try to run all the fuel out of the engine before you put it away for the season. Instead, you should put fuel stabilizer in any and all fuel you use in any piece of equipment you have. The stabilizer is cheap (about $3-$4) and it will treat about 20 gallons of gas. I recommend running it year round because gas sitting for as little as a week can start to go stale, especially during the summer when the fuels have a large percentage of ethanol that evaporates quickly.


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## cadblaster (Sep 17, 2005)

bbnissan said:


> I hate to say this, but this will do absolutely nothing to help your piece of equipment. Even when you run "all the fuel out of it", there is still a rather large quanity of fuel left in the bowl of the carb. This fuel will sit and varnish up the jets and passages in the carb and make it run like you are describing.
> 
> You need to pull the carb apart and clean it thoroughly. Also make sure you get the very very tiny holes between the treads of the "bolt" that holds the bowl on (there should be 1-3 of them depending on the carb).


Well to be precise I used to run it til it ran out of gas then choke it and run it until I couldn't get it to fire anymore. This did a pretty good job of getting most of the fuel out of the bowl, and It always started right up the following year. When I pulled the carb apart the bowl was pretty clean, in fact I could't find much of any dirt, varish or other deposits in it. I've cleaned out the carb twice, because the first time I was using a partial can of cleaner and I didn't have enough. All of the passages have been cleaned with solvent and blown out with compressed air only (to prevent damaging any orifice). 

These constant speed engines don't have much adjustmenet to the carbs. It's getting fuel, I can go and start it right now. I just can't gte it to maintain a constant rpm. This is what led me to thinking that maybe I don't have a fuel problem. I am baffled.


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