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James W
James W, Small Engine Troubleshooting Expert
Category: Small Engine
Satisfied Customers: 3708
Experience:  7 years as Mechanic & Parts Manager for Brother who has Owned Lawn & Garden Repair shop for 35 years
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Ariens ST824 Snowblower with a Tecumseh HM80 155316P engine

Customer Question

I have an old Ariens ST824 Snow blower with a Tecumseh HM80 155316P (Ser.   #   92790) engine. I rebuilt the carb last year. It starts good; however, it will not run smooth. There are always minor misfires that keep the engine from running smoothly. I can adjust the main adjustment screw (high speed) one or two rotations either direction and that makes very little difference in the way the engine runs. It continues to have minor misfires and the engines rpms vary somewhat.

Thanks for your suggestions.

Submitted: 5 years ago.
Category: Small Engine
Expert:  James W replied 5 years ago.


There are many things that can help, none the least of are replacing the spark plug. How old is it?

James W and other Small Engine Specialists are ready to help you
Expert:  James W replied 5 years ago.

I understand you just cleaned the carburetor, some of this may not apply, but still the information will be helpful.

I expect you have either a fuel Quality or fuel delivery problem Still..

As engines sit or get older, fuel that is left in the carburetor can turn to gum and varnish and cause this and other problems.

Also, any gasoline that was left in a gas can for a period of more than 30 days must be discarded because it also has begun to turn to varnish.

Today's gasolines contain MTBE and alcohol. (Ethanol) They turn to "Junk and garbage" very quickly. Alcohol absorbs water. And they call it "Oxygenated fuels! It is the oxygen (and the water) that breaks down the organic compounds in the fuel and turns the gas to "Garbage" (Gum and varnish) The fuels we had just a few years ago had no alcohol in it and would store for longer periods of time before going stale.

Fuel stabilizers do almost nothing to prevent the fuel from going bad with the changes in today's fuels. The whole point of a fuel stabilizer is to form an oily film on the surface of stored gasoline whether in the tank or in a gas can. The idea was to keep oxygen away from the gasoline to prevent breakdown. Since the fuel is already oxygenated, the fuel stabilizer concept is null and void. These fuels start to degrade immediately upon the addition of the ethanol.

Do not buy gas from the "Discount" Stations. The discount stations get a reduced price on gas because they may be buying fuel that is nearly 30 days old already. You may be getting fuel that's nearly stale right from the pump when buying from a discount station. Purchase your fuel from the well-known stations such as Shell, BP, Sonoco, Phillips 66 etc.

More than 70% of all of our repairs in our small engine repair business are due to these same issues. You most likely have dirt, gum, varnish...etc in your carburetor plugging up the small passageways and jets in the carburetor.

The carburetor will need to be cleaned and overhauled as well as the rest of the fuel system.

  • If you plan to do the work yourself, take pictures with your digital camera or at least make a drawing of where all the linkages, gaskets, and component parts go. Correct reassembly is critical.
  • Remove the carburetor from the engine.
  • Remove all of the non-metallic parts since the carburetor cleaner will cause them to be disfigured decompose and plug the carburetor as time goes on.
  • Clean all parts with carburetor cleaner.
  • Blow out all the small holes and passageways with compressed air.
  • Use a tiny stiff wire such as is found on the twist tie on a loaf of bread or on a garbage bag to open all tiny passageways found in the carburetor such as in the screw, nut, or jet holding the bowl of the carburetor on (if it has a bowl). Make sure to look for tiny holes in the bottom and side threads of the bowl nut or nozzle a make sure they are clear with the wire.
  • Wash the carburetor cleaner off of the metal parts by washing them in warm, soapy water then rinsing with clean water.
  • Dry all carburetor parts by blowing it off with compressed air.
  • Make sure that all the passageways are blown dry before reassembling (you do not want water back in the carburetor).
  • Reassemble the carburetor using a NEW carburetor rebuild kit.
  • NOTE: DO NOT TRY TO REASSEMBLE WITHOUT USING A COMPLETE CARBURETOR KIT! You will just end up having to do the job again.
  • Find the Model, type and serial or code numbers off of the engine and take them to your local dealer to get the carburetor repair kit.
  • ALWAYS clean the fuel tank and replace the fuel line when doing this repair or you may have to do it all over again. The inside of the fuel line disintegrates over time and these small pieces of rubber will plug up the carburetor too. Dirt and water from a dirty fuel tank will also plug up the carburetor. If this happens, you will be starting over again from the top.

In an Emergency such as a blizzard where you cannot get out to buy a carburetor kit until the plows come through, or during an emergency power outage and you need a generator running even if it runs poorly, you might try the following if your carburetor is the type that has a bowl. Sometimes this procedure works:

While the carburetor is still mounted to the engine:

  • Pinch the fuel line with a pair of vice grips to stop the fuel from going to the carburetor.
  • Remove the bowl nut (or nozzle from the bottom of the carburetor and let the fuel drain from the bowl.
  • Carefully remove the bowl from the carburetor without letting the needle and seat and float fall out of position (if it does, no big deal, but you will have to reassemble it, which is harder with the carburetor on the unit).
  • Dump all of the Gunk out of the bowl and put the bowl back into position.
  • Use a tiny stiff wire such as is found on the twist tie on a loaf of bread or on a garbage bag to open all tiny holes in the screw, bowl nut, or nozzle that was holding the bowl of the carburetor on (if it has a bowl). Make sure to look for tiny holes in the bottom and side threads of the bowl nut or nozzle a make sure they are clear with the wire.
  • Reassemble and see if you got lucky.

You may be able to finish the job at hand then clean and overhaul the carburetor correctly when you have more time and a new carburetor overhaul kit.

If you don't feel comfortable with these kinds of repairs, or if the carburetor still doesn't work correctly after your attempt, I would suggest sending it to a profession repair shop with a reputation for having friendly, knowledgeable, experienced service technicians. It would be best to take it to someone who has an "Ultra-sonic" cleaning machine. This machine uses a very mild carburetor cleaner in concert with ultrasonic vibrations to get the very small passageways clean. This method is very effective even when traditional methods fail.

Please feel free to ask follow-up questions so that we can always arrive at the correct solution.

Customer: replied 5 years ago.
The fuel system is clean. I completely disassembled the carb last summer and rebuilt the carb. The snowblower wasn't used that much last winter. All the fuel was drained out of the system when it was stored over the winter (including the bowl). We just started the engine recently. I removed the bowl yesterday and it was very clean. I also replaced the high speed needle yesterday. I believe the carb is clean. I will replace the spark plug; however, it was replaced last fall. Any other suggestions?
Expert:  James W replied 5 years ago.

can you manually manipulate the governor assembly while adjusting the carb.

You should be able to rev it up quickly and smoothly when the carb is adjusted properly and good and clean.

There are two sides to the carb, the low speed and the high speed.

I will be that there is one little oriface somewhere that is still plugged up.

Perhaps underneath a welch plug (that is why I say use a carb kit..

If it runs all the time whithout stopping then the ign is good.

Compression is OK or else it would not start easy.

Is it possible there is a bloackage in the muffler?

Perhaps a dirty fuel filter or dirty screen in the gas tank?