1979 Lawn-Boy 2-cycle carb adjustment? Other mixture adjustment?

[Peabody]

I have an ancient 2-cycle Lawn-Boy mower (model 7086) that uses gas/oil mixture. It doesn't run very smoothly anymore, and the spark plug fouls pretty easily/frequently.

The other day I shut the main gas line off and let it run until the carburetor bowl emptied and the engine died. But I noticed that in the middle of that process, the engine smoothed out real nice, and also sped up a bit. Well, I'm wonderinging if the bowl is filling up too much under normal operation, producing too rich a mixture. That could make sense if whatever shuts off the gas inflow as the float comes up has gotten old or compressed or whatever in the last

27 years, so that the float has to go higher to shut off the fuel.

After that, I took the carb off, took it apart and cleaned it. And I discovered a screw adjustment on the side that I hadn't seen before. Can someone tell me what this is for, and how it should be adjusted? Could I use it to compensate for the aging of the fuel inlet gizmo so the mixure is leaned out a bit? The adjustment looks a lot like the "idle adjustment" screw you used to find on auto engines, but I don't know if it performs the same function.

Otherwise, do I have to buy a new carb the get the mixture right? I would hate to have to do that. It would probably cost more than the mower. Could I just bend the float arm? I don't see any way to check what the fuel level in the bowl is, or should be.

[Jeff]

Most older engines have several adjustments. High speed mixture--a needle valve usually adjusted by running engine at high speed and making leaner until engine rpm drops, back off a bit from this, further tweaking may be required under load. Idle speed usually a screw to prevent the throttle from completely closing, sometimes there is also a needle valve controlling the idle mixture. Usually set idle speed so engine idles smoothly and adjust idle mixture same way as high speed mixture. Engine should not stutter on quickly opening the throttle. This may require several iterations to get right.

[m Ransley]

If you are lucky it is a mixture adjustment, turning it in will lean it of gas, try it turn it in till it runs best.

[John Lawrence]

[Peabody]

Thanks. This one only has one adjustment screw. It's not obvious what it controls.

Well, I'll play with it and see what happens.

Thanks