MTD lawn mower running rough


Old 04-29-00, 08:15 PM
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I have a 3 year old MTD 22inch mower with a 4 horse Briggs and Straton engine. It starts good, but then runs rough, or misses, with diminshed power. I have replaced the spark plug twice. added dry gas to the gasoline, and removed the air filter temporarily. What else could be the problem?
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Old 04-29-00, 09:29 PM
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Hi:Terry Ringer

Sounds like the governor linkage may have dirt on it. This will cause it to resist reacting quickly to speed changes or cause it to bindup at a low speed setting.

Once it slides to a slow point it will stick there causing a sluggish running speed.

May also be a restricted fuel filter or even a plugged or restricted vent cap on the fuel tank.

Try running the engine as normally but without the fuel cap on. If this corrects the problem, clear the vent hole. It's located just under the cover inside the cap.

Check for other possible fuel restrictions and also the choke linkage. Move the choke by hand and be sure it moves freely also.

Good Luck

TomBartco: Accurate Power Equipment Company.
Trade:Natural Gas Energy Consultant & Technician.
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Vocations:Saw & Tool Sharpening. Small Engine Repairs.

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Old 05-08-00, 02:27 PM
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It sounds like it was left to the elements. Do you store your mower inside?

The first thing I do is take my air compressor and blow of whatever dirt or oil is on the mower, They should be kept clean.
Too much dirt and oil clumped on the engine keeps it from air cooling properly and will shorten the life of the mower. You can use a water hose if you do the tune up. When using a hose keep the spray away from the gas cap. so you don't get water into the gas tank. It can even go in through the threaded part of the cap.

What I would do is just a little tune up,
Take the gas tank off, when you unplug the fuel line put your finger over the hole on the bottom of the gas tank so the gas doesn't spill out. Then empty the gas and let it air dry or if you have an air compressor you can shoot air into it and get the old gas out. Then take the air filter and clean it with soap and water, thoroughly... Let it dry.

Then take the float bowl off and clean it so you could eat out it while your there you should take the needle valve out and clean it or replace it but be careful with it so you don't scratch it all up.

I would explain how to change the points and condensor but most likely their fine if its starting good. I would take the cover off my engine and clean the magnets on the side of the flywheel. Its also good to clean the magneto but you may not be able to get it back in adjustment and cleaning the magnets on the flywheel should be good enough. You can steel wool but wipe it off with a clean rag then put the cover back on.

Pull the oil drain square bolt under the engine and drain the oil. let it drain thoroughly.
While there take the blade off and if you have sharpened it check that it is balanced. If its worn or damaged buy a new one, their cheap. To check if its balanced drive a 8 penny nail into a wall or board. lightly oil the nail, make the nail level, put the center hole of the blade just past the head of the nail so it can move freely. if one side of the blade is higher than the other its off balanced could be from too much sharpening on one side not enough on the other or just wore that way... Put the blade on snuggly.

Afterwards put the drain bolt back in and put new fresh oil back in. Don't go over max on the oil dipstick.

Now if its dry put the fuel tank back on, hook the fuel line back up.
Once the air filter has dried put some oil on a rag and dab it lightly on the outside of the filter, it doesn't take hardly any oil.

Make a good cover for the engine out of a tough plastic and buy a short bungy to tie around the base of the cover and engine... cover the engine when the mowers not being used. Even when its inside it can still detour spiders and other small bugs... I have fixed alot of mower that were just filled with spider webs.

Hope I helped, Its the easiest way to get Some performance out of your mower.
good luck,
Old 10-19-08, 08:05 PM
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hey terry,
thanks for the detailed steps. my push mower just started acting up today as we were doing the last cut of the season, go figure the perfect timing..
Anyway, your steps are excellent.
Question please: in my attempt to clean all the trash out I loosened the magneto then read more carefully that this may require some fine tuning during re-assembly.
what is the proper gap between the magneto and flywheel?
Also, there is a plastic tube that runs from the gas tank to a place close to the exhaust manifold. It's light blue and about the diameter of a cigar. There's a hairline crack in it, should I replace it while I have the motor exposed or let it be? Any idea what it's called?

Thanks again for taking the time to list out the steps. I'm hoping that with your suggestions and a limited amount of knuckle-busting I'll get my MTD (4hp B&S) cutting again. Only this time I'll be sure to take better care of it in the off season.

Old 10-19-08, 08:30 PM
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Hi TN, welcome to the diy site. The post you are responding to is very old (8 years) and the original poster is no longer a member here.

The part you are describing is the intake tube, and if it has a crack, it should be replaced as it can draw air through the crack and cause the mixture to become too lean. This can make your engine hard to start, hunt and loose power. Without your specific model number from your engine I can only guess that the armature air gap should be .006" - .010".

You can download the Briggs check chart here and with your model number you can see what the settings for your engine should be.
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