2-Stroke Lawn-Boy Engine Won't Run

Beltzington · May 28, 2016

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 · May 28, 2016

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 · May 28, 2016

Bird said:
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 · May 28, 2016

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

Bird · May 28, 2016

tcartwri said:
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 · May 28, 2016

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 · May 28, 2016

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 · May 28, 2016

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 · May 28, 2016

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 · May 28, 2016

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.

CalG · May 29, 2016

2458n said:
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.

Guys

Readthe op

It DID start on fluid, (but not run long). Now it does not start.
First thing needed is to get it to start again.. You know fuel, air, compression, and ignition. just the way the OP stated.

It's just that he got all sideways with the governor hardware which has absolutely nothing to do with starting unless it's got the throttle plate closed and choking the carb . Flooded ?

Bladehauler · Jun 18, 2016

I loved MY old Lawnboy, had it 25 years till the ex destroyed it .
Theres no choke on those, they used a primer bulb setup , and if its cracked or the lines bad or put on backwards its a no go.Mine would always try to start off the primer even if the carb was plugged.
My .02 and where I'd start since the O.P already verified ignition is working by getting it to start off either.
Pilot or emulsion tubes ( what I call em ) and main jets clean and a working primer system should have you mowing with a grin !
P.S I think I always ran mine at 32 to 1 , usually off left over gas from my race bikes.

Bladehauler · Jun 18, 2016

And just now noticed the last post from dam near a month ago , so.....

Toyboy · Jun 19, 2016

Well if he continued to use starting fluid to get it going, the mowers probably toast by now. Two cycle engines rely on the oil in the fuel to lubricate them. Without that your running metal to metal. Starting fluid and two strokes just don't get along. Lots of people forget about that aspect.

RalphVa · Jun 20, 2016

Loved my Lawnboy but gave it away to Habitat when the differential locked up.

Had to replace the electronic spark module once. Used some of that carb cleaner gasoline additive that I keep forgetting the name of (in white can) when carb got a little funny.

Ralph

RalphVa · Jun 20, 2016

SeaFoam fuel treatment is the stuff. Used it once or twice in the Lawnboy when it either wouldn't run just right or wouldn't idle right. Fixed it right up.

Ralph

ultrarunner · Jun 20, 2016

I have a 1980 Toro Commercial two stroke walk behind mower with aluminum deck...

Gave my neighbor $25 for it when he was moving overseas...

Good, well built mower.

Mom was over a couple of weeks ago and wanted to mow... when she ran out of gas she reached for my gas can and put in straight gas...

Have not tried to see if it still works... suppose to have 50 to 1

She said it ran out when she was almost done.

I'm wondering if it is toast?

Only way to find out is to drain the tank and refill with my Stihl 50:1 mix...

My fault in that why would anyone know what fuel a 35 year old mower would use...

https://www.google.com/url?sa=i&rct...BoUTvdqfXmVORhdqjmMCq15g&ust=1466551227570658

Industrial Toys · Jun 20, 2016

I had a couple in the 80s. I think I farted around with them enough. One threw a stone threw it's magnesium deck. Not a pretty sight.

My trick for starting any such small engine is to hold a propane torch (unlit) up to the carb intake, with the filter off. If it has spark, it usually starts. It beats pulling, til you rip out the cord. Sometimes it helps to have someone hold the torch.

ultrarunner · Jun 21, 2016

Makes sense and a great tip!

ch1ch2 · Jun 21, 2016

Industrial Toys said:
I had a couple in the 80s. I think I farted around with them enough. One threw a stone threw it's magnesium deck. Not a pretty sight.

My trick for starting any such small engine is to hold a propane torch (unlit) up to the carb intake, with the filter off. If it has spark, it usually starts. It beats pulling, til you rip out the cord. Sometimes it helps to have someone hold the torch.

Never heard of that one.
I have used propane to find vacuum leaks.