Snowblower engine troubles (HMSK100)

My snowblower (10hp Tecumseh Snow King engine HMSK100) is actually working quite well except for one little thing that I can't figure out.

When it's under load (blowing snow at full power) it seems to run really well. It's only when the load is off and it's still running at high speed that it's misfiring quite a bit. I've messed with the main jet during this but it doesn't seem to help.

Go back into the snow, misfire gone. Weird? Anyone have any suggestions? This past fall I took the carb apart and cleaned it up pretty well. While I had it apart I changed the carb bowl gasket, intake gasket, and replaced the float. New plug installed as well.

I've noticed as well that when you reduce throttle to almost cut off, like almost at idle speed that it really starts to loop.....rev up rev down rev up rev down etc. I guess the first place to start is the fuel?

 

Carb is still dirty. Carb needs to be taken a part again and soaked in a carb cleaning solution, rinsed off, blow out ALL holes with compressed air. Some tiny pin hole inside the carb are varnished up and soaking is the ONLY way to dissolve the varnish. Spray carb cleaner will NOT work on the inner workings of the carb.

 

it's misfire as opposed to hunting/surging?

 

When running full throttle with no load it misfires. When throttled back it seems to hunt/surge.

Hmm, wouldn't the engine run like crap if the carb was dirty? It runs great under load

 

Nope. There are 3 "circuts" in the carb. 1) low speed (idle). 2) mid range. 3). High speed. Each "circut" is independant of each other except for mid range which uses both low speed & high speed circuts. Your problem is in the low speed circut. As I said before, a pinhole is varnished up and the only way to remove the varnish is by soaking. You can not see these pin holes as they are inside the carb casting.

 

One sec now.....

My problem is definitely not in the low speed.....well not entirely. Yeah it hunts a bit at low idle but the original issue is at high speed (wide open throttle) but not blowing snow (ie not under a load).

 

Indypower is right.. Even tho you have the throttle in the wide open position,, the govenor is controlling the engine speed & @ 3600 rpm with no load,, the throttle is only off the idle screw.. That's why it runs good under load, (the carb is using the "hi"circuit ) 'cus everyting is OK there,, but @ fast idle, (or slow) the idle circuit is blocked.. Do a search for Geogrubbs posts as he has Excellent pics of the most common problem with Tecumseh carbs.. The main jet has the idle passage blocked & possible the idle passage in the carb... Soak it in a bath type cleaner & install a complete kit & you'll be O.K.... Roger

 

Excellent.....ok sorry about the confusion! I think I know what has to be done

 

My brain is trying to understand this.....having a hard time.

My confusion is with the throttle at wide open but not under a load. The governor is controlling it here and limiting the amount of throttle obviously. You say it is only working off the idle circuit at this point though? I guess that makes sense but how could you ever make adjustments to the main jet screw if that's the case? If it was only operating off the idle circuit, wouldn't adjustments to the main jet do very little?

The engine manual says to make your carb adjustments at idle and then at wide open throttle (actually the other way around I think) but if your operating the engine unloaded (as you would be when making initial adjustments) and it is indeed only using the idle circuit at this point, what's the point of adjusting anything but the idle screw?

Maybe I'm missing something.

 

You guys were right on..... Well sorta.

I readjusted the carb and my idle adjustment screw was off. Once I set it properly and after a little fine tuning it's running smoothly.

I still am a little confused, read my last post, but thanks so much for the help!