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Discussion Starter #1
Hey guys, I really need some help here. I was given a snowblower and I can't get it to run properly.
It's a 10hp Tecumseh - HMSK100 - 159456W. The problem is that I can't get the engine to stop surging I was going to do a carb job on it but instead was convinced to get a brand new, non-adjustable carb. So I put that in and made sure all the linkages were in the same slots as before. Then adjusted the governor with the throttle wide open and there is plenty of tension on the throttle spring. Fired it up and it still runs like crap. So my next thing was valve adjustments. I pulled the head, cleaned out all the carbon and just in there. Inspected the valves and they seem to be in good condition. No pitting or warping. The clearance called for
.008-.012 for both valves so I went with a happy medium at .010. Cleaned everything nice, installed a new head gasket with the head. Put a brand new spark plug in and fired it up. And it still runs really bad. I changed the fuel line and primer hose just to be sure there's no leaks and still can't get it running good.

I'm at a loss for what else it could be? Unless it's a faulty carb. Any advice on which direction to go next would be greatly appreciated. This one has me stumped
 

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Have you checked the condition of the gaskets on both ends of the intake manifold?
It's not unheard of to find shavings from machining in a brand new carb either.
I had replaced my worn out carb with one from oregon and it ran terrible. I found a used carb in decent condition and rebuilt it and now it runs great.
If your old carbs' throttle shaft isn't slopped out, you should rebuild it.
 

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Discussion Starter #3
All new gaskets all around on the intake ends, new head gasket, and new gaskets on the crankcase breather (after doing the valves). I should have mentioned earlier that I bought 2 of the same new carbs because I also needed one for another snowblower. I put a carb kit in the original carb and all 3 carbs do the same thing. So I am fairly certain it is not a carb issue
 

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Discussion Starter #5
Just set the armature gap to .020 and wire wheeled the magnets. Good thinking but it sadly didn't help.
 

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Sounds like you're into the governor/throttle linkage next. Do you have another engine to copy the link connection placements? If not, post pics of it as is. The PO could have done some accidental mischief while attempting a fix.

I just found a hm100 with the throttle lever spring inserted in the wrong hole/slot- that was enough to cause surge and more.
I usually adjust the governor lever in the middle instead of using the manual procedure - seems to work better.
Good luck to you!
 

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Discussion Starter #7
This is the pic of my linkage setup.
I'll have to try setting the governor to the middle instead of it all the way to the end.
 

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This is the pic of my linkage setup.
I'll have to try setting the governor to the middle instead of it all the way to the end.

my linkage is in the same as yours just went and checked
try this start it up and get warmed up while its surging hold the gov arm and see if the surging stops
gov could be adjusted wrong take a pic of the arm is it forward toard the carb or pointed away from the carb when you look at it?
 

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Discussion Starter #10
This is the governor arm setting. I loosened the torx screw, open the throttle lever up on high, turned the governor clamp clockwise as far as it would go and tightened the screw back up. I'm going to try the half governor thing right now
 

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Discussion Starter #11
So I'm definitely thinking it's something with the governor. If I set it a tittle lower than turned all the way it revs way out of control. But if I loosen the throttle spring screw I can get it to town down and somewhat run clean. I might just have to find the perfect sweet spot for it
 

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So I'm definitely thinking it's something with the governor. If I set it a tittle lower than turned all the way it revs way out of control. But if I loosen the throttle spring screw I can get it to town down and somewhat run clean. I might just have to find the perfect sweet spot for it
The gov arm isnt away from the carb it looks right
you need a tach and set max rpms at 3600 via the torx screw behind the throttle arm
myself i adjust my 8 hp gov arm back more then what yours is so i can run 3725 for eod
 

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Discussion Starter #13
my linkage is in the same as yours just went and checked
try this start it up and get warmed up while its surging hold the gov arm and see if the surging stops
gov could be adjusted wrong take a pic of the arm is it forward toard the carb or pointed away from the carb when you look at it?
The surging does stop if I hold the governor. But as soon as I let it go it starts again no matter what RPM.
I don't have a tach so I've kind of just always adjusted by ear but have never had any problems like this
 

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surging is usually related to fuel air mix ratio.
u need to check fuel delivery from gas cap all the way to intake valve .
gas cap, tank outlet port, fuel shutoff valve , fuel line, carb inlet,needle valve, float, jets, mixture screws, fuel /air passages, intake pipe and gaskets.
also possible is a bad/intermittent/weak spark
 

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Discussion Starter #15
surging is usually related to fuel air mix ratio.
u need to check fuel delivery from gas cap all the way to intake valve .
gas cap, tank outlet port, fuel shutoff valve , fuel line, carb inlet,needle valve, float, jets, mixture screws, fuel /air passages, intake pipe and gaskets.
also possible is a bad/intermittent/weak spark
I've replaced the old fuel line with new, as well as the primer line. Made sure there's no kinks or restrictions. When I press on the dump valve on the bottom of the carb bowl I get a full steady stream of gas. I was thinking all the same things as yourself. Now my spark plug is starting to look like this, which is worrisome. Does the color of how the plug is burning point anyone in a better direction?
 

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looks a little too hot, running lean. either too much air or too little gas.
any backfire? u check the gap? spray carb cleaner at both intake gaskets for air leaks?
if u spray carb cleaner into choke opening do revs even out.
if u partially close choke does it help
 

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Discussion Starter #17
looks a little too hot, running lean. either too much air or too little gas.
any backfire? u check the gap? spray carb cleaner at both intake gaskets for air leaks?
if u spray carb cleaner into choke opening do revs even out.
if u partially close choke does it help
I have it apart right now so I can't run it. Even though I put all new gaskets an air leak would make a lot of sense. I'm gonna to take the whole carb and manifold apart and check and double check and recheck to see if there is a small crack in the manifold or a bad gasket.

What about the little diaphragm one way valve on the crank case breather filter? That's the only thing I haven't tampered with yet. I'll post a pic of what I'm talking about.
 

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I have it apart right now so I can't run it. Even though I put all new gaskets an air leak would make a lot of sense. I'm gonna to take the whole carb and manifold apart and check and double check and recheck to see if there is a small crack in the manifold or a bad gasket.

What about the little diaphragm one way valve on the crank case breather filter? That's the only thing I haven't tampered with yet. I'll post a pic of what I'm talking about.
ive never really heard that diaphragm giving any1 a problem espicially for surging, imo.

i also have a 10hp, from the 80's though, flathead. cleaned mine 3 times b4 i got it right, finally, it used to run like crap, surge and backfire, but bought a clone off ebay and runs similar, both are the adjustable type, if u can buy that and never the non adjustable.
closing choke will reveal if it was running lean, surging, backfiring.

spraying carb cleaner or similar volatiles will easily find any air intake leaks, using propane from a torch is also a good option and better imo. u can also use it on the air intake side where the choke is to see if rpms level out.

some people do widen/drill out the main jet to get more fuel into the motor if they have a non adjustable carb which is why if replacing a carb people get one that is adjustable even though the original was not.

as the engine gets older it sometimes the only way to get it to rev correctly.
or they just get used to partially closing the choke....or maybe try a higher octane fuel, that might help, u never know
 

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Never seen the tecs ive worked surging fron being lean they will if theres any crap in there they will
buy and adjustable carb for 12 bucks and be done with it
set low speed screw 1 turn out
the hi speed screw 1.5 turns out
 

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Never seen the tecs ive worked surging fron being lean they will if theres any crap in there they will
buy and adjustable carb for 12 bucks and be done with it
set low speed screw 1 turn out
the hi speed screw 1.5 turns out
agreed, if it was an air leak it should run lean consistently, so it sounds more like of a fuel issue, carb is not letting enough get in consistently, in which case it variably runs lean, but he swears carb is clean with out any debris. buy ya, should of bought an adjustable, cheap enough to get and snows not here yet.
 
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