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Jon K.
Jon K., Small Engine Diagnostic Expert
Category: Small Engine
Satisfied Customers: 5783
Experience:  Gold certified Stihl tech, Service Manager for a rental/repair shop.Certified in most small engines
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I have a craftsman snowblower model 536.881850. The engine

Customer Question

I have a craftsman snowblower modelNNN-NN-NNNN The engine starts easily, will run well while blowing snow, but then stalls after about 10 minutes and won't restart until it cools completely. Thinking a component in the ignition system was failing due to heat, I checked for spark immediately after last stall. Spark looked perfect. It seems like the engine is running hot. Please help! This snowthrower is not very old and has only been used a few times.
Submitted: 3 years ago.
Category: Small Engine
Expert:  Jon K. replied 3 years 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.

Is there an adjustable jet on the bottom of your carberator that looks like this?

graphic

Customer: replied 3 years ago.
No. In fact there are no adjustments at all on the carb except for the end stop for the throttle position.
Expert:  Jon K. replied 3 years ago.
Ok I thought that maybe being an older machine that we would be able to adjust the carburetor back to where it needed to be. If you are getting spark after the engine dies then your ignition system should be fine. Let's check something simple that happens all the time. Remove your gas cap and look at the underside of it. You should see a metal disc. Very often this disc falls off and will cover the outlet to your fuel tank. If this is the case then you will need to fish the metal disc out of the tank and replace the gas cap.
Customer: replied 3 years ago.

The metal disk is connected to the gas cap as it should be.

Expert:  Jon K. replied 3 years ago.

Ok So we know the fuel is not getting blocked off and that you are getting spark after the engine dies, that leaves the carburetor. You are going to need to clean out the carburetor and main jet, hopefully this will fix your hot (lean) running condition.

 

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 side of the engine you will see the carburetor float bowl with your main jet in the center. Remove this jet 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 will also need to clean the jet thoroughly including the little hole 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 3 years ago.

So. I forgot to mention that I already cleaned the carb. Here is the background . . . I have had the blower for three years. The first year it ran great. The second year it ran well, but I had to keep the choke on all the time to get the engine to run right. After some reading, I reasoned that the carb was dirty. I bought a gallon can of "chem dip" carb cleaner. I disassembled the carb (removed all plastic and rubber parts) and submerged the carb in the chem dip for 30 minutes. After removing from the chem-dip, I washed the carb with water and cleaned all the orifaces with compressed air. Then I reassembled the carb, attached it to the motor and restarted the blower to check to see if it would warm up and run with the choke off. I repeated this chem dip process five times before the engine would run with the choke off. I also replaced the gasket between the carb and intake manifold.

 

How can I tell if the engine is running lean?

 

 

 

 

 

Expert:  Jon K. replied 3 years ago.

A lean running engine will run much hotter then a normal engine. If your muffler is starting to glow that is a good indicator. Also if you remove the spark plug the tip will appear white if the engine is running lean.

In all accounts this does sound like a classic ignition problem. When an ignition coil starts to go bad, it will stop producing spark when it gets hot. After it cools down it will begin to spark. As time goes on it will loose it's ability to create spark all together. Because you are immediately getting spark this is throwing me off.

I still believe that your problem is in the carb. Just because it has been dipped and cleaned does not guarantee that it will function correctly.

Does this engine run smooth when it is running?

Customer: replied 3 years ago.
No, the engine does not run smooth when it is running. Let me describe the engine's behavior from a cold start: With the engine off, I set the choke to full on. After one pull, the engine starts. Within a minute I move the choke from full to half, and within 7 minutes I move the choke to full off. Then, with the engine warmed up and running and the choke fully off, the engine does not run smooth. The engine speed oscillates from slow to fast, such that in about 10 seconds the engine speed has risen and fallen 15 times. This engine does not have a manual throttle, and so the throttle position is governed by a mechanical control system (tied to the main crankshaft, if I understand correctly), and I can clearly see the throttle on the carb opening and closing repeatedly. So, it is like the engine speed control is not working properly. THEN, if I move the choke to half on, the engine will run smoothly at a constant speed.
Expert:  Jon K. replied 3 years ago.

You most definitely have a carburation issue. The osculating is the engines governor trying to compensate for the lack of fuel being delivered. Using the choke to smooth out the engine is the same as changing the jets inside the carburetor. By lessening the amount of air being drawn into the carburetor you are increasing the fuel ratio (the amount of fuel does not change, just the air fuel ration) At this point after cleaning your carburetor this many times and as thoroughly as you have I would probably replace it. The only other option is to bring the carb to a shop that has a sonic cleaner. These little machines are what jewelers use to clean jewelery and are extremely effective in cleaning out the hidden orifices in these carburetors. You also have welch plugs in the carburetor that if not sealed properly will allow the low and high speed circuits to cross and mix the two air fuel ratio's at the wrong time.

My professional opinion would be to replace the carb if cost effective.

Customer: replied 3 years ago.
Thanks for your opinion. I have ordered a new carb ($45) that will arrive this coming Wednesday. I will install it shortly thereafter, test the snowblower, and then respond to you with the outcome.
Expert:  Jon K. replied 3 years ago.
I'm hoping for the best for you. $45 is a GREAT price for a new carburetor
Jon K., Small Engine Diagnostic Expert
Category: Small Engine
Satisfied Customers: 5783
Experience: Gold certified Stihl tech, Service Manager for a rental/repair shop.Certified in most small engines
Jon K. and 3 other Small Engine Specialists are ready to help you
Customer: replied 3 years ago.

Hi Jon,

 

Just put the new carb on and the blower runs great. The "osscilating from slow to fast" engine speed problem is gone, and now the engine runs smoothly. Also, the engine RPM's were much higher before the carb change, and now they seem much more reasonable.

 

Thanks again for your help!

 

- Matt

Expert:  Jon K. replied 3 years ago.
Great news, I am glad to hear everything worked out for you. Thank you very much for the bonus!

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