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Just lucked out while out driving the countryside the other day--a free Lawn Boy lawnmower at the end of someone's driveway. Looks like it was used very recently. I have been looking online to try and find a manual for this mower, but so far no luck. Lawn Boy's website doesn't recognize the Model # CS21ZSM, Serial # K175B0435 (label is on top of mower and is very clear--says it's a Commercial 21 mower). This model has no battery, does have a plastic gas tank.

Questions:

1. Is there a manual choke? Where is it?
2. What else should I be aware of before trying to start it (it still has some gas in it, so don't have to worry about mixing oil/gas--instructions are on gas cap anyway about how much oil/gas to mix)
3. Is the lever for self-propelled the bottom or the top one (there are 2 levers)?

Assume it is like any other two stroke engine. The choke is going to be somewhere on the carb. Push the priming bulb 10 times and then make sure the choke is on. Pull the cord until you hear the engine "first fire." It'll sound like it runs for a second and then off. Now turn the choke off. Pull the cord again. It should start up. You said it has been run recently, so it will probably start for you. But since its on the road it probably hasn;t been run recently. If it doesn't start, don't be surprised if the carb needs a cleaning and it may need a new spark plug. And make sure the air filter is clean. If its clogged with junk the mower probably wont start.

By the way I wouldn't be so sure of that gas thats already in it since you found it on the road. Dont even try with that stuff. Dump it and put fresh gas+oil in it.

For the oil mix, 2 stokes take a 30:1, 40:1, or 50:1. Just mix it 40:1 and you'll be fine. Or get one of those one gallon mixes.

Thanks to "crazyoldtractor" for your help. I guess I will just go with "trial & error" and hope for the best.

MeMyself said:

Just lucked out while out driving the countryside the other day--a free Lawn Boy lawnmower at the end of someone's driveway. Looks like it was used very recently. I have been looking online to try and find a manual for this mower, but so far no luck. Lawn Boy's website doesn't recognize the Model # CS21ZSM, Serial # K175B0435 (label is on top of mower and is very clear--says it's a Commercial 21 mower). This model has no battery, does have a plastic gas tank.

Questions:

1. Is there a manual choke? Where is it?
2. What else should I be aware of before trying to start it (it still has some gas in it, so don't have to worry about mixing oil/gas--instructions are on gas cap anyway about how much oil/gas to mix)
3. Is the lever for self-propelled the bottom or the top one (there are 2 levers)?

Click to expand...

I don't think that's a valid model number. Most Lawn-Boys have a name plate on the rear of the deck with both the serial number and the model number. Please look again.

You got a great deal -- free! :wink: Congratulations. And welcome to the forum, MeMyself.

There's a good section devoted to Lawn-Boy -- I hope you'll check that out -- and post some pictures. That might help someone ID this mower.

I hope maybe I helped a bit. Be aware that you have a mower that is very very hard to come by these days. Take good care of it.

-Brandon

+1 on starting over with at least a known mix of fresh gas and a premium 2-stroke oil.:biggrin: Probably 70% of the junk I try to get running has fuel issues.

Another +1 for starting with fresh fuel. Also, you likely have a model S21ZSM, made in 1991 (by the 'K' in the serial number. Manuals and parts lists are available online.

I recommend using the oil ratio listed for the unit as too lean a mixture would not lubricate sufficiently and might burn up the engine. The good old 2-cycle Lawn-Boy's are awesome mowers, I would recommend getting it fixed up and running if it doesn't need anything too pricey.