2-Stroke Lawn-Boy Engine Won't Run

[Beltzington]

Fuel, air and spark how hard could it be? Hoping someone has some experience with the Lawn-Boy 4600 Push mower, two-stroke, single cylinder.

I bought this new in 1982 and used it for 16-years and it ran before I put it in storage in 1998. A few weeks ago a was looking for a better solution than weed whacking a steep ditch and dug the mower out of the shed. Wouldn't start initially but I could get it to start with starting fluid but it will not continue to run. Unsurprisingly I found some cracked or disconnected fuel and vacuum lines which I fixed, pulled the carb and it seems in good condition but there is a throttle valve on the carb I do not fully understand how it should be adjusted. The mower has two engine speeds, rabbit and hare. The selection lever for these settings is connected to the throttle valve which basically is moved to wide-open on fast and partially closed for slow. The kicker is the throttle valve's exact position is determined by a wind vane and a spring, the wind vane is deflected when the engine is running by radial-impellers on top of the engine. It is really a simple design to automatically keep the engine speed constant under varying loads and my hat is off to the engineer who came up with this solution but I have no idea how to adjust it. When I had the carb off I found the spring was disconnected from the throttle valve so I reconnected it and stupidly "adjusted" the spring tension to open the valve wide open when set to rabbit, and now after putting it all back together I can't get it to start even with starting fluid.

I am guessing the valve might also operate as a choke for startup but I could sure use some help from someone whose knuckles don't hang as close to the ground as mine.

 

[Bird]

I haven't had a two stroke Lawnboy since 1989 when I sold the house and became a full time RVer. But at that time, I gave away a good Lawnboy that I'd been using for about 16 years. Those were the best lawnmowers ever made as far as I'm concerned. I assume you put fresh gas in it. The only other trouble I ever had with mine was fixed by replacing the points and condenser.

 

[Beltzington]

I haven't had a two stroke Lawnboy since 1989 when I sold the house and became a full time RVer. But at that time, I gave away a good Lawnboy that I'd been using for about 16 years. Those were the best lawnmowers ever made as far as I'm concerned. I assume you put fresh gas in it. The only other trouble I ever had with mine was fixed by replacing the points and condenser.

Yes fresh gas, I guess I will need to start over with the basics, no reason I can see it should not at least fire with starting fluid. Maybe I just fouled the plug, during troubleshooting. Would really like to get it working as with the aluminum deck and 2-stroke it would be perfect for cleaning up around the pond, but seems everyone is specializing nowadays, even small engine shops. I asked the folks where I get parts for my Stihl equipment and they didn't even want to look at it.

 

[tcartwri]

Equally important on a two stroke..... The muffler. If it's sludged up or plugged the engine will not run.

 

[Bird]

Equally important on a two stroke..... The muffler. If it's sludged up or plugged the engine will not run.

Good point; one I'd forgotten.

 

[JimRB]

It takes me 20 minutes max to cut my Mom's lawn, if the mower will run. It kept stalling.

Toro 2 stroke. I had cleaned out the muffler and the easy start port a few years ago so that was not the issue. I thought I would try a new fuel line and filter as the line was mushy. That did not help. Carb semi on and off a few times. Linkage prevented me from taking it totally off. Anyhow taking off the main jet and the pilot tube and making sure they were clean, flushing what was left of the carb with carb cleaner a few times and 40 psi from the air compressor got the mower running again. 20 minute job took 3 hours. Hopefully it will start and work next time I have to mow. The neighborhood kid usually mows.

The pilot tube has gotten me a few times on Honda 4 stroke mowers too.

 

[CalG]

It's probably flooded.

remove the spark plug and clear out any surplus fuel. Then disconnect the fuel line from the carb so you eliminate fuel delivery settings etc.

Then give a little squirt of fuel in the plug hole before screwing the plug home. Give a few pulls with the throttle valve fully open. if it starts and runs out the fuel, You have it down to the carb settings.

If it still doesn't start, try again with a new spark plug. Then start looking at "all the other stuff."

I've got a similar Lawn-Boy. maybe a bit older, self propelled. I bought it used over twenty years ago. Had to put a new coil/pickup assembly on it last summer.

 

[2458n]

Gas has to be mixed with oil. Starting fluid does not have and after 16 years of setting any gas has plugged up the carb. A mower that old has a good tip speed on the blade. Government has since reduced this. Clean carb with spray, replace lines, clean muffler, new spark plug and mixed gas. The farm had a old Western Auto Wizzard mower that ran for 50 years-until the renter ran regular gas in it.

 

[timster2]

I just fixed the same problem on an old lawn boy mower. A neighbor had not used the mower in twenty years. It would run on starting fluid but would not keep running. It turned out to be a plugged main jet in the carb. I took a thin wire, one strand from an old throttle cable, and pushed it through from the inside of the carb. Flushed it out with some carb cleaner and it now runs good.

 

[Kyle_in_Tex]

I have also seen stuff get caught in the reed valves like pieces of deteriorated foam air filter or very small sticks or blades of coarse grass. Check your compression.