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Jon K.
Jon K., Small Engine Diagnostic Expert
Category: Small Engine
Satisfied Customers: 5786
Experience:  Gold certified Stihl tech, Service Manager for a rental/repair shop.Certified in most small engines
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Tecumseh 8hp MTD 26" snow thrower idles up and down, up and

Resolved Question:

Tecumseh 8hp MTD 26" snow thrower idles up and down, up and down with and without load. Slight backfire on down side of the idle surge. Engine has a govenor but not sure how those work, yet. I am mechanically inclined and can read and follow drawings. Does the carb affect the govenor or does the govenor directly control the carb? Can the carb cause this up and down idle condition?

Thanks, Derek.
Submitted: 1 year ago.
Category: Small Engine
Expert:  Jon K. replied 1 year ago.

Thank you for choosing Just Answer, my name is XXXXX XXXXX I will do my best to help you find the answer you need to resolve your problem.

Your carburetor is 100% your problem. You need to clean out your carburetor; your machine is starving for Fuel.

First turn of your fuel or pinch off the fuel line.

Turn you machine on its snout so that the handles are facing straight up in the air.

On the left side of the engine you will see the carburetor float bowl with your
main jet in the center.This is directly under the square box that has the
throttle control and the key in it Remove this jet (the ½ inch bolt in the
middle) by unscrewing it and gently remove the bowl inspecting to see if there
is any debris inside it. Clean the bowl and spray some carb cleaner straight up
and into the hole the jet was unscrewed from. (you can get away without the
carb cleaner if it is not too bad) You will also need to clean the jet
thoroughly including the little hole (a bread tie wire works well for this or a
similar small wire) not just the big one (see picture) Once everything is clean
set the machine back on it's wheels and turn the fuel on allowing fuel to run
through into a drip pan for about 10 seconds.

Stand the machine back up and reassemble. This should get you going.

graphic





Customer: replied 1 year ago.


Cool thanks, XXXXX XXXXX try that now and let you know soon.

Expert:  Jon K. replied 1 year ago.
If it is just revving up and down but running cleaning that jet should clear up your problem
Customer: replied 1 year ago.

I took the jet out and cleaned it with carb cleaner and a wire as you recommended and I verified the jet is clear, both holes including the very, very tiny one that you would not notice unless looking for it. I also dropped the bowl to check that and I found some "goo" like old gas that jelled up, not much but some. Cleaned and back together but the idle still goes up and down, maybe even a little more now. What should I look at next?

Expert:  Jon K. replied 1 year ago.

You are going to have to really clean out the carburetor now, maybe even rebuild it. What is the model number off your engine. Once I have this I can send you directions on how to go about this.

That goo is old gas and is probably clogging up some of the passages in your carburetor

Customer: replied 1 year ago.


Tecumseh model number "LH318SA". 318cc, also had "SPEC 156553G" on tag if needed.

Expert:  Jon K. replied 1 year ago.

Thank you

Before you do a complete tear down I want to try one more cleaning trick. Using the link at the bottom open up picture number 2. I want you to remove this small jet (it probably has a plastic cover over it, just pry that off) Unscrew that and spray some carb cleaner into the hole and then using that small wire run it inside this little jet the same as you did on the large one. Reassemble and try it. If this does not work then you are going to have to go through all the cleaning. Make sure to pay attention to pictures numbers 13 and 14. If this fails then you will need to disassemble the entire carburetor and soak it overnight in a commercial carburetor cleaner, then rebuild it with a new carb kit. Even after all of this there is a chance the carburetor will not come clean and will need to be rebuilt. At almost $100 for the carb we need to try everything else first

Do not remove any linkages without diagramming them first

http://outdoorpowerinfo.com/repairs/tecumseh_carb_640084b.asp

Customer: replied 1 year ago.

Thanks, XXXXX XXXXX let you know very soon how and if that jet cleaning worked.

Expert:  Jon K. replied 1 year ago.
I'll be here, best of luck to you.
Customer: replied 1 year ago.


Well, it's gonna be a remove and rebuild I think. Not sure if this is normal but when I was looking in the muffler while it was running I noticed it was getting cherry red inside. Indication of lean but would the exhaust port on the engine look like that normally?

Expert:  Jon K. replied 1 year ago.
yes when the carb ports are clogged up and the machine revs up and down like that, it is running very lean and it will very often make the muffler glow like that. I've seen the whole muffler turn cherry red
Jon K., Small Engine Diagnostic Expert
Category: Small Engine
Satisfied Customers: 5786
Experience: Gold certified Stihl tech, Service Manager for a rental/repair shop.Certified in most small engines
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