adjusting carburator on lawnmower

I have adopted a Craftsman self-propelled mower. It is about 25 years old but has not been used for the last 10 years. The engine is unmarked so I honestly have no idea of the horsepower or brand. It has the high wheels in the back for rough ground so I assume it is a fairly powerful engine, as lawnmowers go. After an oil change,
(pudding came out) and clean plug, I got it started. It starts great and does not smoke. BUT I can not get the motor to run fast enough to cut grass well.

I know enough to know I need to adjust the idle and fuel mix but the silly thing has 3 screws and I don't know which one to turn which way. Add to that that the idiot who designed it has the hot exhaust blowing right at your hand while you try to turn the screws so I can only make quick adjustments or get burned.

There is a screw in the center bottom of the carburator, a thick one on the side, (fuel mix, I think) and one near the top, sort of recessed, throttle maybe? Which needs to turn in, that is tighter, and which out for a fast smooth run?

Right now, I estimate I am getting 50-75 percent of the RPM it is capable of. Also it runs unevenly, faster then slower, without me changing the throttle though I have been able to improve that somewhat.

All assistance appreciated.

Re: adjusting carburator on lawnmower

#3429 06/04/01 09:22 PM

Joined: Dec 1999

Posts: 5,427

Likes: 36

Sydney, NSW, Australia

Bruce

Repair Junkie

The screw in the bottom of the carby bowl is the high speed mixture screw. Screw it in clockwise till it bottoms then screw out 1 & 1/2 turns. I would then run the mower at full speed and open the screw until it starts to run rough then back in till it starts to smooth out.

Once that is right then you adjust the idle screw which is just above the carby bowl. This one screw in clockwise till it bottoms then bring out 1 turn. Then start and bring the throttle back to the idle position and adjust the srew till it is running smooth.

The other screw is the idle speed screw which you adjust to the speed required.

Regards,
Bruce

Regards,