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lawn boy starting problems

15 years ago

I just picked up a 1991, Model C21ZMRB, commercial Lawn-Boy

for $10.00 that looks to be in great condition. It starts

right up when it's cold, but after it gets hot, it will

start on the first pull only if it is within 10 seconds or less after shut-down. So if you are slow while emptying the bagger, it won't start. If you take out the spark plug and pull the starter rope 3 or 4 times, then put the plug back in, it will then start back up. Does anyone have an idea what the problem might be and if it is worth repairing?

Thanks, Russell

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Comments (12)

grn68rt
15 years ago
It could be the coil but don't trust me on that. I had a machine that did that and I replaced the coil and it's been fine since. I don't know if it's a coincidence or not.
rdaystrom
15 years ago
Sounds like it could be a heat related coil problem like grn68rt said. During that time when it will not start do an immediate spark check by laying a known good plug on the side of the engine with the wire attached and give it a pull. You may need an assistant for this. Should be a nice blue spark. If no spark or yellow spark then it's probably the coil.
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This is a 'real' Lawn-Boy with a somewhat complicated engine-management/governor system rather than the simple air vane/spring system of the later models. I haven't worked on one like that but there are a number of adjustments/parts that control engine speed. So I'll defer to others, like 'Walt' who has experience with them. But, there are still some things to check. The first thing is it is entirely possible that with the age of the mower and the fact that you have used it without an air filter element that it has lost adequate compression to develop power. Another common problem on old LBs is hard carbon build-up in the exhaust ports and muffler assembly. Assuming you used the right crankshaft seals and installed them correctly, and they haven't blown out of position, that factor should be okay. Contamination in the carb from lack of air filter could be another. The ignition coils have two-phase operation, where the 'start' phase works up to 800 RPM, then the 'run' phase takes over. If the 'run' phase in your coil is not working, it would act like you describe. That's about all I have. Hope you can solve it.
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walt2002
15 years ago
From your description, I would say that the float needle is leaking a little and floods it. After cooling down, gas has evaporated. Try turning off gas line shut off valve 15 seconds or so before stopping engine.

Another possibility, wrong or bad plug.

Walt Conner
thing
Original Author
15 years ago
I have checked the coil several times and it always is putting out a strong spark when it want start.When I pull the plug out and spin the engine good and hard then put the plug back in it will start right up.I have ruled out flooding as a problem so why would spinning the engine with the plug out seem to fix it? Thanks,Russell
walt2002
15 years ago
"I have ruled out flooding as a problem"

How?

When you remove the plug, have you held it up to see if there is a hair size "filament of carb between the electrodes?

Walt Conner
thing
Original Author
15 years ago
I have two new correct plugs that I have used which is how I ruled out that as the problem.I had someone say that it could be a vacumm? problem.I am at a loss. Russell
walt2002
15 years ago
My question was how did you rule out flooding. What does new spark plugs have to do with that?

Walt Conner
thing
Original Author
15 years ago
I always thought if it was flooded that the plug would be wet with gas.If that isn't always the case then how do check for flooding?You also asked if I held up the plug could I see a hair size filament of carb between the electrodes.I have and both plugs seem to be fine. Russell
walt2002
15 years ago
I suspect the fuel may be saturating the air filter which would not show up on the spark plug. I made some other suggestions for checks which I have not seen an reply about but maybe others have better ideas.

Over and out,

Walt Conner
thing
Original Author
15 years ago
Walt,The air filter element does'nt seem to be getting saturated but I have noticed that after it runs a while and then sits overnight there are several drips of fuel coming from the bottom of the air filter housing.I am going to turn off the fuel valve as you suggested and see what happens.Thanks
roserx
15 years ago
My 5247 has a similar problem. It cranks 1st or 2nd try when it's cold, but if you let it run out of gas and have to fill it up, it takes dozens of pulls on the cord to re-crank it.
thing
Original Author
15 years ago
Thanks Walt,I was only looking to see if the plug was getting wet from flooding but it has a small drip coming out from under the filter.Does anyone know where to find carb parts for this thing?

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