Lawn-Boy 2 Cycle Running Question


Old 06-20-05, 07:04 AM
PCkid's Avatar
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Join Date: Jun 2005
Location: Tennessee
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Question Lawn-Boy 2 Cycle Running Question

I have been given a Lawn-Boy M series 4,5 hp 2 cycle mower. It has tanks for gas and oil. I have never used one of these mowers and was wondering about the way the motor runs. I know most 2 cycle engines run with what sounds like a miss in the engine. This one starts and runs and mows great even through tall grass. It does not bog down or stall even under heavy loads.

The one thing I notice is that the engine runs a little rough when idling and sounds like it has a miss. I also hear some of this when mowing. I put in new plug and rebuilt the carb but really didnt make any difference.

Is this normal on these older 2 cycle mowers or is there something going on that I have missed.

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Old 06-20-05, 10:08 PM
repair_guy's Avatar
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Location: Marion,Al.
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Lawn-Boy 2 Cycle

A 2 cycle engine does not run "smooth" anyway.the older M and F series through,both had points.I think(it's been a long time).The way you described the running of the mower sounds like the contact points (under the flywheel) may be dirty or out of adjustment.I have no Lawnboy books,but if memory serves they set at 0.18.The air gap on the ignition coil is something like 0.006.
Old 06-21-05, 03:24 AM
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Location: Upstate New York
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Before you remove the flywheel, lets be sure you have points. What is the model and serial number of your machine? You may well have a typical running 2-stroker.
Old 06-21-05, 04:56 PM
PCkid's Avatar
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Join Date: Jun 2005
Location: Tennessee
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Lawnboy 2 Cycle Running

It is an old M21BMR (1988) which from what I found in the parts list online it has a CD ignition and no points.

I used it today and mowed for an hour and it mows great. I talked to a local lawn-boy dealer here and the tech said it was normal for the engine to run with what sounds like a miss as they ran them rich when not under load to get enough lubrication into engine. Under load it settles down quite a lot.

Have never tried one of these 2 cycle mowers but if they all are like this one they are one mowing machine. This is a commercial version and still looks almost like new after 17 years..

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