S21ZPN Issue - Lawn Mower Forums : Lawnmower Reviews, Repair, Pricing and Discussion Forum
 
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post #1 of 8 (permalink) Old 04-19-2020, 01:35 PM Thread Starter
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S21ZPN Issue

Just joined the forum because, well, I suddenly have an issue with my 30+ year old Lawn Boy.

I was mowing and pushed mower under spruce tree and short branch seemed to affect throttle. Mower fell to a low idle speed, stalled and would not stop. Moving throttle lever had no effect. I removed air cleaner, assembly and unfortunately carburator (Walbro LMR 1). Now can't figure out where longer end of governor spring attaches to.

No obvious damage, thinking branch could have dislodged spring, of course, could be something else.

I have the manual but photos are unclear, been looking online unsuccessfully. Need it back together to see if it will run, then further work if necessary. Really love this mower, don't want to have to replace it.

This is a choke carb, not a primer bulb bit like some Lawn Boys

FYI, I am original owner and always maintained this mower.

This may also be known as a 4275 model (S21ZPN and s/n G263C0763 are on label, note s/n does not sync with S21ZPN according to literature, thinking is should be an H).

Need help, hate to take it to a shop as competence level is not high.

Mike
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post #2 of 8 (permalink) Old 04-19-2020, 02:10 PM Thread Starter
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Guys, figured it out, there was a black lever with a downturned hook I did not see, hooked it up, reassembled and she fired on the 2nd pull.

Greatest mower ever made!

Mike
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post #3 of 8 (permalink) Old 04-20-2020, 09:21 AM
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Glad to hear you got it figured out Mike and that it was a simple fix. I have found the Lawnboy 2 cycle mowers to be relatively simple to use, operate, and maintain as long as you understand the basics. Just love being able to go out to mow with a machine that is 45 to 50 years old and it starts on one or two pulls. Too bad mowers of this quality aren't made anymore. Bill

Also, welcome to the forum. Lots of knowledgeable folks here with plenty to share.

1968 Lawnboy 3054 Mower
1973 Lawnboy 8231 Mower
1975 Lawnboy 5024 Mower
1975 Lawnboy 5273 Mower
1976 Lawnboy 5274 Mower
1977 Lawnboy 5024 Mower
1980 Lawnboy 7268 Mower
1982 Lawnboy 5247 Mower
1982 Lawnboy 5247 Mower
1972 Lawnboy 1015 Edger
1972 Lawnboy 1015 Edger
1987 Lawnboy 1400CL Trimmer

Where there's a will, there's Mr. Bill!
They don't call me MacGyver for nothing!
I have LBAD and DCAD!
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post #4 of 8 (permalink) Old 04-20-2020, 11:13 AM Thread Starter
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Bill,

Thanks, yeah, i got lucky and figured it out, fluke issue. I agree it is a great mower. The few neighbors that do actually mow their lawns here go thru crappy mowers every 3 or 4 years, they have to be wondering why my green Lawn Boy always runs. One of the few tools I won't loan out.

Any way to check rpm other than by sound, my ancient dwell tach obviously won't work on this puppy.

Mike
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post #5 of 8 (permalink) Old 04-20-2020, 11:49 AM
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Hi Mike! My favorite tach is the Treysit Vibratach made in Germany. Works with a vibrating wire. Love it and it is accurate with my digital and my Lawnboy Mower Monitor. You can also buy cheap digital ones that wrap or clip to the plug wire. Also some physically read the RPM using reflective tape on a rotating mass. Bill

Attached Images
File Type: jpg Lawnboy Mower Monitor OMC ET-301.JPG (1.83 MB, 1 views)

1968 Lawnboy 3054 Mower
1973 Lawnboy 8231 Mower
1975 Lawnboy 5024 Mower
1975 Lawnboy 5273 Mower
1976 Lawnboy 5274 Mower
1977 Lawnboy 5024 Mower
1980 Lawnboy 7268 Mower
1982 Lawnboy 5247 Mower
1982 Lawnboy 5247 Mower
1972 Lawnboy 1015 Edger
1972 Lawnboy 1015 Edger
1987 Lawnboy 1400CL Trimmer

Where there's a will, there's Mr. Bill!
They don't call me MacGyver for nothing!
I have LBAD and DCAD!
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post #6 of 8 (permalink) Old 04-20-2020, 02:43 PM Thread Starter
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Bill,

Thanks for info, that gizmo is pretty cool. Might be handy for checking my turntable speed also!
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post #7 of 8 (permalink) Old 04-21-2020, 07:47 PM
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That mower looks just like the one we had when I was a teenager! Not sure of the model #.
Always started and ran great, would cut grass that would choke and kill a Briggs.
I think my younger brother has it now.
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post #8 of 8 (permalink) Old 04-24-2020, 03:28 PM
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Yes I agree, probably one of the best mowers ever made. I have basically the same mower, but it's a 1992 model, I think yours might be a 1990 or 91 model judging from your serial number. There seems to be no limit to the service life of these 2 stroke push mowers.
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