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Briggs Snow Engine oscillates

Posted by vinnie_s NJ (My Page) on
Sat, Jan 29, 11 at 10:02

This is the 7.5 HP Briggs engine on a Craftsman snowblower. The choke switch is a 5 position switch (left choke to right fo run). It starts easy and runs smoothest with the in the center position. However, if I leave it in this center position, the engine almosts stalls when I engage the auger, but recovers. When I move it all the way right to the "run" position, is oscillates. In the run position, it does not stall or want to stall under load, and does run. However, it oscillates up and down.

Gas is always fresh and always has Sta-bil in it.

I have attached a video link of the oscillation:

http://s224.photobucket.com/albums/dd78/yankees_1996/?action=view¤t=Video91.mp4

Any ideas?


Follow-Up Postings:

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RE: Briggs Snow Engine oscillates

  • Posted by ericwi Dane County WI (My Page) on
    Sat, Jan 29, 11 at 16:25

Usually the change in engine rpms, also called hunting, is caused by an accumulation of varnish in the carburetor. If the engine is more than three years old, that is more likely to be the case, since varnish accumulates over time. Since you are able to get the engine started, and keep it running, you might want to try adding some carburetor cleaner, gum-out, or something similar, to the gas. My experience has been that this works, but it can take two hours of operation before the engine settles down and runs smoothly. I do not think it is a good idea to use carb cleaner all the time, because it can chemically attack plastic parts, o-rings, and rubber hoses.


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RE: Briggs Snow Engine oscillates

Depending on how cold the weather is and how long the engine was running it just maybe cold hence the 5 positions of the choke. IMO you will have to find the right air/fuel ratio for the temp. your operating in untill the engine gets up to operating speed and then depending on the zero factor you may still have to choke if off alittle? I once seen it so cold in Neb. my old ford truck wouldn't come of themostatic controlled choke setting.


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RE: Briggs Snow Engine oscillates

It was warm. Had been running for at least 5 minutes. Was like 30 or so degrees.


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RE: Briggs Snow Engine oscillates

I would follow Ericwi thought process . Try Some Lucas top end that is both a lubricant and cleaner 2 ounces usually will eliminate the fouling problem . Ensure fresh fuel prior to adding the carb cleaner . I hope the oscillates discription is your way of describing a rough running engine lol.


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RE: Briggs Snow Engine oscillates

We still don't know how old or new it is or how long it's been setting? I know my new tiller with briggs inlek 6.5 engine would hunt after being in storage until it got all the air out of the fuel system and warmed up, also seem like the gov. design was awlful touchy and would hunt with little load on the engine.

If this thing has set for while then the carb maybe gummed up as suggested (buy you can of spary carb. cleaner and read the instuctions and go to work degumming it). IMO it don't take much for new briggs engine to start hunting espeically if you don't use them. Then again it could be fouled plug, dirty air filter, or carb. out of adjustment too lean for cold operations. who knows with little history.


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RE: Briggs Snow Engine oscillates

Oscillation! LOL

Tells you what I know about gas engines. I can do basic repair, maintenance removing and reinstalling. But I do not know how they function. That is why I asked about the carb. Removing it looks fairly easy on this unit.

I definitely do like the correction made with "hunting". I had no idea what it was. I don't think the engine is running rough. I also considered rough more like erratic and misfire. This is just hunting. It starts super easy and really runs pretty good.


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RE: Briggs Snow Engine oscillates

Hunting is normally an indication of a lean running engine . You can try the cleaning as advised to allow more fuel flow or attempt to enrichen the air fuel mixture via the low speed jet . Turn the jet out an 1/8 to 1/4 turn and see if it helps with the idle and hunting issues . Also if someone has improperly set the governor you would experience some erratic engine behaviour.


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RE: Briggs Snow Engine oscillates

"I do not think it is a good idea to use carb cleaner all the time, because it can chemically attack plastic parts, o-rings, and rubber hoses".

I had 34 year old 3 1/2 hp tiller that I bet I cleaned the carb. 30 times, plus the tank, and head. Never once did I ever replace a gasket, not even the head gasket.

What do you think in the liquid your pouring in? I guessing airsol or liquid all the same chemicals. IMO airsol is better because it evaporates very quickly. I buy gum-out like beerbellies by beer, if it hurt any seals none of my equipment would run.

I wish I could just plug a can in like propane and just run if off that, disconnect when your done? think about it never have to clean or worry about stale fuel setting in the fuel system.

I don't know why small equipment not being ran off those little green jug of propane anyway. Could have 40 lb bottle to recharge all the little green ones???????


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RE: Briggs Snow Engine oscillates

The snowblower is about from 2004 or so. It was the first year Briggs got back into snow engines. Plug is new. I used the crap out of it the last 3 years.


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RE: Briggs Snow Engine oscillates

  • Posted by ericwi Dane County WI (My Page) on
    Sun, Jan 30, 11 at 22:50

I can't be certain that carburetor varnish is the cause of your symptoms, but I had the exact same problem with a lawnmower, about 6 years old. Carb cleaner did the trick, although I think it took about three successive lawn mowings to get the problem completely solved. Our snowblower has a fuel line valve, and I am closing the valve, and letting the carb run dry, 'till the engine quits, every time I am done. I agree with RCMoser, a propane fuel source would make small engines more reliable.


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