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J.R., Small Engine Technician
Category: Small Engine
Satisfied Customers: 7445
Experience:  Owner of outdoor power equipment business, repairing all makes and models.
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Good Morning, I have a 1997 MTD Yard Machines Limited Edition

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Good Morning,

I have a 1997 MTD Yard Machines Limited Edition riding lawn mower. It has a Briggs and Stratton 18.5 HP engine with a Aisan carburetor. The B&S Model number is: 303777. The Type is: 1032-A1 1880. The Code is 96112211.

The carb sits on the side of the manifold instead of on the top like most carbs do.
My problem is that the engine runs great as long as the air cleaner is removed. As soon as the air cleaner is installed the engine loads up and starts missing and smoking. As soon as the air is removed it clears right up and runs great again. It has this condition at idle or at fast idle and seems to load up about the same in either throttle position.

I used my LED light to check for light coming through the filter and it has good light all the way around. The B&S part number matches as to what it should be. Can this type of carb be so sensitive to dirt in air filter that it can look good but still cause this problem?

The problem is most likely a plugged up jet in the carb, not an air filter problem. Pull the carb off and give it a good cleaning.
Customer: replied 7 years ago.
Hi J.R.

I pulled the carb off and completely disasembled it. Then I sprayed cleaner through all of the passages to make sure it came out of the other ends. The I blew through the passages both ways if possible. I did the same thing with the main jet, idle jet, emulsion tube etc.
I also check to make sure all the little holes werent pluged in them.

If you feel that the carb is clean, then I would replace the air filter. The filter may be dirty enough that it is affecting the air/fuel mixture. Does it have a green pre filter on it?
Customer: replied 7 years ago.
It does have a green pre filter on it but the engine runs the same with or without the pre filter on the air cleaner.
Change the air cleaner and see if that does not fix it.
J.R. and 2 other Small Engine Specialists are ready to help you
Customer: replied 7 years ago.
I will do that and let you know if it fixes the problem.
Let me know and we will continue if needed.

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