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Discussion Starter #1
HI. I have a snowblower with a tecumseh HMSK100 with what seems like a carb problem. Starts good, idles good, and even at high speed works good but once you start to work it or even just engage auger it wants to stumble or run poorly. You can adjust high speed and get it back and then it will do it again. It seemed like a dirty carb which I cleaned, and today I swapped it out for a good carb and same problem. I have tried spraying carb cleaner around carb and gaskets looking for air leaks but does not make a difference. Any ideas? Could valves cause this problem. Definately an older engine. Thanks

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:welcome:

When you say "adjust high speed", what exactly are you referring to? The high speed needle jet or the throttle position?
 

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One of two problems, still go back to carb, cleaning can be a number of things, the worse the problem, the more you need to do, carb dunk tank, ultrasonic cleaner.

The other is resistance somewhere. Something is difficult to turn, auger shaft, bearings, pulleys. If everything is spinning easily, then carb.
 

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Have you tried to unscrew the gas cap to see if it run better with it off? If it does, you have a gas cap that isn't venting properly. If that's the issue, you can drill a small hole in the gas cap until you get yourself a new one.
 

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Have you tried to unscrew the gas cap to see if it run better with it off? If it does, you have a gas cap that isn't venting properly. If that's the issue, you can drill a small hole in the gas cap until you get yourself a new one.
Good catch. It may be starving for fuel. If it is the grass cap, drill a tiny hole on the side so water didn't get in. If you have a filter, replace it, make sure the fuel line is clear, remove the filter if you have one, remove the fuel bowl and play with the float to see how much fuel is coming out, maybe the float valve is slow to release.
 

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Cold Pepper
My 2 cents on this is awhile back I had a little 5 hp Ariens that started good and idles well. Reving up was good but not immediate but it would still rev at the top limit. I would get into snow and it would loose power and take a bit to get back up to speed, then the same thing when I went back into snow. Carb was clean with new gaskets, fuel was fresh so I was scratching my head. I decided to check the valve clearance and voila, I had one valve not closing all the way. I lapped the valves then set them back to factory specs and after that the machine really went to work on how ever much snow you gave it.
Hope this might help.
Regards
Snoman110
 

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There are quite a few things that can cause this, basically any loss of compression. As snowman said, the valves and seats can wear over time, to the point where they no longer close all the way. I've also seen these things run with a blown head gasket, which is really cool to watch at night! It does the same thing you said - runs fine no load, but no guts under load. Head gaskets for these are pretty cheap, get one with a real fire ring if you can. If it hasn't run in a while, it could be stuck rings. You can check by running a compression test, then putting like half a cap full of oil down the spark plug hole and running a second test. If the compression jumps, it's probably rings. I have a friend who swore you could unstick them by smacking the top of the piston with a block of wood, but I've never tried it. The most pain in the *** one is if the valve seats have worked their way loose, that usually only happens if the engine has overheated from either compromised cooling (mice nests in the blower housing) or overrevving.

Others have mentioned fuel starvation, but normally that presents as having power for the first few minutes after starting (while the float bowl is still full) and then dying as the bowl empties and the fuel supply isn't sufficient to keep it filled. Other things that can cause that are clogged fuel filters, pinched fuel lines, old fuel lines broken down by age and especially ethanol that basically clog themselves (I replace all my fuel lines with ethanol safe ones), and rusted metal fuel shutoffs, especially on older tecumseh metal tanks.

The last thing I'd suggest is the intake gasket. I'm not sure which intake setup you have, but if the intake gasket gets ripped, it becomes a vacuum leak.
 

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Discussion Starter #10
Sorry for delay but I have been away and didn't get a chance to work on it for awhile. The problem was the gas filter screen inside the tank. I tried a new tank and it worked good. I could not see inside tank to see how bad it was, I just cleaned it with brake cleaner etc. I guess what was happening was as long as bowl was full it would start fine and idle but once it started to work the gas could not come in fast enough. Thanks for ideas
 
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