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Craftsman 12hp runs rough under load.


woscarr's Avatar
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08-06-09, 06:38 PM   #1  
Craftsman 12hp runs rough under load.

I have a Craftsman 12hp/38"cut model# 917.255511 lawn tractor that seems to start and run pretty smooth. I was trying it out the other day and was cutting nice, going thru grass 1 to 3" with no probs. but when I hit some really thick grass 4"+ the tractor started to sputter and cough really bad that I had to disengage the blades then it seems to slowly smooth it self out again. I can drive around and even cut grass again but if I hit thick stuff it will do it again.

Where should I be looking to solve this one. I put in new oil and air filter.

Thanks in advance for any advise on this.

Wayne

 
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08-06-09, 07:09 PM   #2  
Usually when someone is having problems with an engine under heavy load, when it runs well otherwise, the main jet circuit is partially plugged or the fuel delivery is restricted.

When this happens the engine has enough fuel to pull a load of up to about 75 % of capacity, but when the governor opens the throttle valve to its max there's not enough fuel to accommodate the demands.

It wouldn't hurt to check the fuel flow going to the carburetor and use a little Sea Foam (from auto parts store) in the gas to clean it up. A lot of times the Sea foam takes care of the problem, but if it still persists the carburetor would have to be adjusted or cleaned.

 
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08-08-09, 06:53 PM   #3  
What kind of engine do you have. Single cylinder OHV briggs like to blow a head gasket internally. They blow between the cylinder and into the space that the push rods go through. This can cause the problems that you describe. This can be difficult to tell with out removing the head to look.

 
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08-09-09, 05:40 AM   #4  
It has the 12hp Tecumseh OHV single cylinder.

I gave the carb a quick clean, haven't tried it yet tho. I plan on giving it a try later today see if I can fine tune the carb. and see if its still doing the same.

I hope its not valves !

Cheers
Wayne

 
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08-09-09, 08:29 AM   #5  
I've never seen that head gasket problem on a Tecumseh and it should not be valves. I agree with marbobj in that it is probably a carb problem. I believe that you have an older model and it should have an adjustable carb. On the side of the carb just above the bowl should be an adjustment screw turning that screw in will lean out the gas mixture. If your are adjusting the carb do just a little at a time. If the problem gets worse than try to back it off and richen the mixture but from your description a little leaner should help. If none of this works then it will have to be cleaned.

Good luck

 
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08-09-09, 12:37 PM   #6  
Hi everyone. I finally got around to trying out the tractor today and it ran perfect. I sprayed out the carb. I put the low speed jet at 1 turn and the high speed at 1.5 and went out into the field to hit some high grass. Sputtered a tad, slight adjustment to the high speed and all is good.

Also noted is how smooth the throttle is between high and low settings now.

Cheers
Wayne

 
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