8 hp Tecumseh (again)

[John_M]

A number of months ago https://www.hearth.com/talk/threads/33211/ I brought up some then-recent problems with this engine on my Ariens snow blower. The then immediate problem was solved, thanks to all your help and T Monter's Service manual. Today, and for the previous 18 years the Tecumseh has started on the first or second pull, no matter the weather, temperature, or how long it has been in storage. A truly great starting engine! And, it now has a new spark plug.

Today, I have some good news to report. Just finished trying to break up some 24" snow drifts in my driveway and the engine ran flawlessly. It performed and sounded like a new engine. However, the snow drifts were packed so hard by the wind I had to stop. I was making no headway and wearing myself to a frazzle.

Now to the point of this post: The outside temperature today is 25 °F. As I recall, the performance problems I have been having this year all occurred when the outdoor temperature was colder and conditions much windier than today's. As a point of info., this engine comes without an air filter but there is a metal shroud surrounding the carburetor. 1) Could the cold temperatures be causing the recent performance problems?; 2) Wind chill cannot affect the performance of an engine, can it?; 3) Because the recent performance problems always occurred during cold and windy conditions is it possible the light and fluffy snow is being blown around by the wind? The carburetor is then sucking in some of this airborne snow which becomes drops of moisture when it enters the carb?

Any thoughts on why the engine would run very well at 25 °F and warmer and sometimes hesitate and buck at 24 °F and colder?

Best, John_M

 

[pen]

You don't make mention of what the current performance problems are.

Most snowblowers that I have come across do not use air cleaners. I would imagine that snow could plug up the air cleaner. If it were doing so, or getting warm and turning the air cleaner to a solid block of ice, I would expect the snowblower to start hesitating and bucking as it would be running rich (just like it would if you turned the choke on while warm).

pen

 

[John_M]

pen, The engine ran very well today. So well, in fact that I was wondering why it ran so eratically a year ago and earlier this year when the temperatures were colder and conditions windier than today. A year ago, during those colder and windier conditions, the engine would run well for a while then start bucking and hesitating when under load. Sometimes, when I backed-up the snowblower the engine would smooth out. Other times, when I loosened the fuel cap the engine would seem to recover and start running well again. Other times it would stall but then restart with only one pull.

Last fall I ran a lot of Sea Foam through the engine and re-tuned the carburetor to factory specs. The engine ran extremely well. However, as soon as the temperature drops below about 24 °F and the wind blows strongly, the erratic running returns. This erratic running during the colder and windier conditions is what I am trying to cure.

Thanks for your interest.

John_M

 

[Deere10]

See if on the carb bowl if there is an adjustable main jet( round knurled screw type deal w a spring wound around it). If so you may have to turn it in or out just a little bit( to richen or lean it out) to compensate for changing temps. Just turn a little bit either way and listen to how it runs. By the way the screw will be in the center of the bowl not off to one side, that is a bowl drain Dont push that or you may get a big gas leak. I have to adjust my Tecumsehs when we get big temp swings. May run fine at 25 the next time when its 0 runs like crap,adjust the screw and its all good..

 

[RobC]

I think Deere 10 is on the money. Rule of thumb. If you tune a blower on a nice fall day and it's running just so sweet, you will go to the lean / rich adjustment and back it out about 1/4 turn. At this point engine should be running like the choke is on, rough. That's the winter setting and where you want it. With where your at now I would suggest either the above or when it's cold out try sliding up the choke 1 click and running it like that and see if it solves problem. Then go and make the carb adjustment.
Rob

 

[SlyFerret]

Is the fuel the same? Or did you mix up a new batch this time around?

-SF

 

[John_M]

Deere, the carburetor does have the main jet, just as you describe. I think you are focusing on the problem area. I'll try making the mixture about 1/16 to 1/8 turn richer at the colder temp. If that does not work I'll try it the same amount leaner and see what happens. I realize that if I turn it 1/8 richer and that does not work I'll have to turn the screw in a full 1/4 from THAT position to make it 1/8 leaner.

Rob, I have already tried "...sliding up the choke one click..." (actually, on my engine you turn it one notch clockwise) and that does help-but not totally. However, I considered this to be more of a temporary fix and I wanted to achieve something more permanent. Perhaps I should look upon these colder temperatures as being a "temporary" condition and use the choke or mixture screw as the "permanent" fix to this temporary condition.

Sly, The fuel I am using now is a new batch, less than month old, with StaBil and Sea Foam added.

Thanks for the help, guys. I'll post again to let you know how this works. John_M

 

[boatboy63]

John, Deere10 is correct in what he said. As the temperature of the air changes, the density changes. When it is colder, the air is denser which will require more fuel (richer) to run properly. Same deal with running an engine at sea level vs on top of a mountain. At sea level, air is more dense and on a mountain, it is thinner.

From your description of the symptoms, if it tries to cut out on you when you pull backwards, you could have some water in the fuel tank. This can happen because of condensation over time as fuel temp may be warmer than air. Water and fuel will not mix. Water is denser and will sink to the bottom of the tank. Your tank may have a lower area in it and the water that has accumulated over time will find this lower area. When you pull back, the water can actually "slosh" out of the lower area and be pulled into the carb, causing it to stall briefly, cough, or stutter. I am a certified marine tech and had a similar situation with a pontoon boat. Customer complained that it ran fine when going forward without turning wheel. As soon as it would turn to the right, it would begin missing, eventually die, and not start back for an hour or so. After troubleshooting, I found there was about 1/2" of water covering the entire bottom of a 20 gallon tank. Marina owner didn't like my theory as it implied he was selling watered down fuel. Come to find out, gas cap had been stolen and rain had splashed into fuel tank for about a month until owner returned and replaced cap. When turning, the water would roll over to 1 side and cause it to get high enough to supply a straight shot of water into the carbs, which killed the engine. The water would get in the bottom of the carb and displace the fuel. If enough water gets into the bottom of the carb, it won't run until either it is drained or slowly evaporates. You may even try draining the float bowl of the carb to see if anything comes out.

If it runs better when the fuel cap is opened, it makes me think you have a vent on the tank that may be partially clogged. This is causing a fuel restriction and making it run leaner since the tank is probably a gravity flow. Check your fuel cap carefully for a tiny pinhole that may be clogged with dirt or snow. Typically this hole is on the top of the cap allowing air to vent the tank so it will gravity feed.