Lawn Boy 5236 low power and problem starting

9 years ago

Hi,
I have a lawn boy mower (5236 d-400 series) that is giving me problems to no end. It has problem starting (even after priming) and when it finally starts, it has very low power. My lawn has very short grass and the moment I push the mower there it just sputters and then dies. It's easier to start when hot but the low power problem still persists.

The plug is in good working condition, the ignition coil is new, and so are the seals. The only thing I am not sure about is the carburetor and governor.

Changing the lever from normal to heavy doesn't seem to affect the power in any way.

I had the carburetor cleaned some time back but seeing that I have been using it without the air filter, it may have took some dirt in. I tried to use a sponge in place of the air filter (which got lost) but the power got so low that the mower went off. I guess there wasn't sufficient air flow. I therefore had to do away with the sponge altogether.

Any help is appreciated.

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Comments (5)

1saxman
9 years ago
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.
walt2002
9 years ago
Well, actually the D-400 did not have the 2 stage coil but true for the later models. He contacted me directly but I was not much help.

Walt Conner
phototone
9 years ago
A mower that old, in all likelyhood has very worn rings which would cause low power output, and soon, no starting. Have you done a compression test?
phototone
9 years ago
Do a compression test. If you have less than 65 lbs. compression (which Lawnboy says is the minimum for a D-400) you need new rings. They are cheap from many vendors (around $6) but labor intensive to replace.
rasims
9 years ago
Another very common problem with these old D-400's, and probably the most common of all, is the primer plunger o-ring failing and allowing excess fuel up through the primer circuit. The easiest way to confirm this is to completely close the main jet by turning the large thumb wheel fully clockwise, if the engine continues to run then obviously fuel is bypassing the main nozzle (jet). It will still continue to run, but it will still be running poorly since it's getting a lot more fuel through the primer circuit than the engine can effectively use. I doubt that low compression is causing this since it will start, usually if the compression is too low with these old 2 strokes they will fail to start at all.