I'm new to the forum. I've owned a Lawn boy a number of years but do not understand what is the difference between a L-series engine and an F-series engine? I have a L21ZPND not sure if this is the model # or not. My lawn boy quit yesterday while mowing. Replace the ignition module and it ran for a little while and quit again. Took off the muffler and looked in the exhaust ports saw the piston had a lot of scratches on it. Anyway getting ready to tear it apart have done so quite awhile back to clean the carbon off the piston head. Like I said before I've had a lawn boy a long time and want to rebuilt this one. I really like the two stroke. Any help would be appreciated. I tried do a search on the L series motor on this web site to no avail. What terms do I need to put in to get a response on a rebuild, thanks.
I have never heard of a L engine, by your model number L21ZPND, I think you have a steel deck 21 inch F powered push mower. The L = steel deck 21= cut width Z= zone start P = push D= 1992 680526 is also a model number for a 1992 mower steel deck 21inch F powered push mower. Check for spark right away when it stops running, and check the gas cap vent for being plugged up. Pull the fuel hose off of the carb and check for full fuel flow.
Hmmm,,,an F series engine is supposed to generate 90 psi cold if you have access to a compression gauge. You could have flash carbon scoring of the cylinder walls or possibly just a stuck ring.
Using a gauge, what reading do you get? When doing a compression test, Pull recoil the number of times required until you come to the maximum reading or it no longer rises. For a F motor the Lawn Boy service manual lists the minimum as 80 psi
