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Hello,

New member here. I have a Lawn Boy S21ZSR that I just can't seem to get running. This mower stopped working a couple years ago. I tried to clean the carb up then but the cable that hold the flywheel brake was stuck and I didn't have more time to spend on it. Fast forward to this last winter and I dragged it back out to get it running.

First order, I disassembled the carb and cleaned it all out again, it was just as clean as I left it. I drained out the little bit of old gas. Next I ordered a replacement cable from Ebay to fix the frozen engine brake cable. It must not have been for this model because it was a bit too long. I cut a piece of pipe to space it out to the correct length. The engine ignition cut off switch still works just fine. Air cleaner and filter are clean. The gas tank is clean and has fresh gas in it. The gas tank filter screen looked clean. Gas drain out of the tank well. I disassembled cleaned and reassembled the gas tank fuel cut off. It has new fuel line and a new fuel filter. I blew air through the fuel line and filter with no restriction. The gas will drain out of the gas tank and out the line at the carb connection point ok. I loosened the float bowl bolt today and gas started to drip out. It appears to me that gas is getting to the carburetor ok.

I have disassembled and cleaned out the carb a few time now, hoping that would fix this, but it's all clean. I sprayed carb cleaner through all the passages, removed the air mixture screw and float needle when I did that. The only thing I didn't remove was the float needle seat, but the carb cleaner blasted right through the carb fuel intake just fine. Choke and throttle cable seems to be working correctly opening and closing the butterfly valves like it should. I've tried to get this mower to run with the air mixture screw at 1.5 turns out, .5 turns out and 3 turns out... nothing works.

Pulling the starter cord ignites a spark in the spark plug, I checked. This mower will start and run on starter fluid (I know it's not he best to use on 2 strokes but this mowers old and if it won't start, it will be scrapped) so I'm assuming that means that the spark is good and it's a fuel issue. Any thoughts?

Is there anything you can suggest I check? My last idea was to remove the float bowl and see if gas drained out. I did that this morning and it seems to be getting gas to the float bowl.

Thank you for any advice.

Did you remove the main jet? There are little holes in the sides that MUST be clean. Depending on your carb they may be very small and if they are plugged you may not see them.
You may also remove the muffler and make sure your exaust ports are clean and unrestricted.
Lee

X2 on the exhaust ports; also I would check compression, should be above 100 on most tester. Best way I have found to test float is to blow air into gas inlet. Turn carb upside down and blow, should not be able to get any air in, place bowl on and turn right side up and blow, air should blow freely into carb, if not you can bend tabs until you get the desired result. I would test float before and go and get a compression tester. I had a walbro carb that the float was out of adjustment and I chased that for a month until I did the blow method. Good luck.

Some of the guys probe the holes. with tiny dia copper wire. You did try choking it?

Thank you all for the suggestions, it's taken me a while to find time to respond. Since my last post I did remove the blot holding on the float bowl while the carb was on the mower. Gas began to run out until I shut off the fuel tank. I may try to run a straight fuel line from the tank and bypass the fuel filter next.


unclelee - I did what you suggested. I removed the muffler and cleaned the exhaust ports. I'd say they were about 10% clogged. It didn't look to me like that would have prevented it. I removed and tore down the carb again. The main jet appears to be pressed in. I couldn't remove it. I tried to pull it out with needle nose pliers, but it felt like that was going to do more damage than good. This is the first carburetor I can remember that doesn't have a main jet that unscrews. Carb cleaner blows through the main jet and out into the air horn (or body, not sure what you would call it) with out restriction it appears.



lewb - Thank you for the suggestion for checking the float. I'll try just that although I'm not sure how well the plastic tab on the float will bend. I'll also check the compression.

motoman - I'll keep that wire trick in mind and see if that might help. I did have the mower in choke position when I tried to start it. The choke flap is working.

After looking up some parts diagrams, I see some carbs similar to this one have an inlet screen for a filter. I'm 99% sure if this one had it, I removed it years ago. I don't remember any screen being there when I tore it apart, but I'll check one more time.

Thank you again for all your advice. The mower runs briefly on starter fluid, so I'm fairly certain it's not electrical/ spark of exhaust port related.

Tunar said:

Thank you all for the suggestions, it's taken me a while to find time to respond. Since my last post I did remove the blot holding on the float bowl while the carb was on the mower. Gas began to run out until I shut off the fuel tank. I may try to run a straight fuel line from the tank and bypass the fuel filter next.


unclelee - I did what you suggested. I removed the muffler and cleaned the exhaust ports. I'd say they were about 10% clogged. It didn't look to me like that would have prevented it. I removed and tore down the carb again. The main jet appears to be pressed in. I couldn't remove it. I tried to pull it out with needle nose pliers, but it felt like that was going to do more damage than good. This is the first carburetor I can remember that doesn't have a main jet that unscrews. Carb cleaner blows through the main jet and out into the air horn (or body, not sure what you would call it) with out restriction it appears.

View attachment 28456View attachment 28457

lewb - Thank you for the suggestion for checking the float. I'll try just that although I'm not sure how well the plastic tab on the float will bend. I'll also check the compression.

motoman - I'll keep that wire trick in mind and see if that might help. I did have the mower in choke position when I tried to start it. The choke flap is working.

After looking up some parts diagrams, I see some carbs similar to this one have an inlet screen for a filter. I'm 99% sure if this one had it, I removed it years ago. I don't remember any screen being there when I tore it apart, but I'll check one more time.

Thank you again for all your advice. The mower runs briefly on starter fluid, so I'm fairly certain it's not electrical/ spark of exhaust port related.

Click to expand...

If that is the case then a new needle, valve and float may be your only fix, does not sound like this is your issue. Looking at the parts diagram, does not list a jet assembly, might be fixed part of carb as far as I can tell. I have never had that style of carb apart so no first hand experience. You could also try ebay for a replacement.

Regarding starter-fluid start...

Is air filter installed?

Where are you squirting in the starter fluid? In the carb throat? Sparkplug hole?

...trying to think of other differences between starter-fluid start and gas start that could give a clue.

Well one final update. Thank you all for your great suggestions. I was absolutely stumped on this one. My uncle gave me this mower (he couldn't get it started, but it just needed new gas) in the mid 90's. We used it about twice a week for a Family Landscaping Business we have. About 4 years ago the mower stopped working. I parked it to fix it and kind of forgot why it stopped by the time I got time to tinker with it. The blade brake cable was frozen, I think this is why I parked it. So I fixed that. Then it just wouldn't start. It had spark and fired with starter fluid squirted into the carburetor with the air filter off. I did a lot of what you all suggested. I did try to check the compression, it would peak about 90 if I recall correctly, but it's 2 stroke, so I really don't know how you can check the compression.

I'm certain it can run again, It's probably something with the carburetor. Possibly a new one would fix that but maybe just a carb kit. I just couldn't spend more time or money on it. I have a garage full of other stuff I need to fix including a newer Lawn Boy I originally bought for my mom and a commercial Snapper self propelled push mower my dad bought me when I was about 10. I hope I'll get some more good suggestions if I need them then.

I sold the Lawn Boy for $25 to a new owner this week. Good luck to him, I'd really like to think that mower has some life left to it. I was a really good mower that provided us with 15 or more years of service. He has time to tinker with it and worked fixing mowers when he was younger. I hope he finds his way to this forum if he need any help.

Pass the torch, life is too short and there are always plenty of rats that always need killing!