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post #1 of 17 Old 07-05-2019, 03:36 PM Thread Starter
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Dumb lawn boy question

Just got an old john deere 12sb, with a lawn boy f engine. Is it bad practice to shut off the fuel shutoff and let it run dry after use, or should I only do this for winter storage. Thanks.
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post #2 of 17 Old 07-05-2019, 05:11 PM
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Re: Dumb lawn boy question

I wouldn't think this would cause much harm. Only possible harm might be to a cheap shut off becoming leaky or stuck. There are brass shut offs available to replace the plastic ones.

I have a B&S 6.5 hp on my Cyclone Rake and I believe that the shut off lever, simply cuts off the fuel supply. At least the little ICONs on the carb show fuel open / fuel closed.

Maybe I should look under the tins since the engine stops immediately when moved to fuel closed position. Seems that there would be some fuel in the bowl for a minute or two of run time after fuel shut off. Or, maybe its a combo fuel and ignition cut off.

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post #3 of 17 Old 07-05-2019, 05:38 PM
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Re: Dumb lawn boy question

I have done it both ways but since I always year around use Stabil in my fuel it doesn't seem to make any difference if I do or don't close the valve. Roger
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post #4 of 17 Old 07-05-2019, 05:42 PM
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Re: Dumb lawn boy question

a four cycle engine will tolerate having the fuel cut off because it is still being lubricated. a two cycle won't because the lubrication is the oil you mix with the fuel. shutting off the fuel lets the engine run lean and will prematurely wear out the piston, rings and bearings.

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post #5 of 17 Old 07-05-2019, 06:19 PM Thread Starter
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Thanks everyone. I will just turn the fuel off while storing, after turning ignition off, as long as the carb seems ok with it.
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post #6 of 17 Old 07-05-2019, 06:20 PM
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Shutting off the fuel supply and letting it run out of fuel is not any different than running out of mix while mowing, however there is really no benefit to doing this unless the mower will be stored for a longer term such as over the winter months. Can't say whether there have been any studies done as to whether this practice of shutting off the fuel and letting the engine come to a stop every time will cause premature failure or not but my guess would be that there is enough residual oil internally so as to not cause any problems. If anyone has any concrete information (studies) regarding this, be sure to post them. I do shut off the fuel supply when the mower has stopped as a precaution to a leaking needle. Bill

1968 Lawnboy Model 3054******1973 Lawnboy Model 8231******1974 Lawnboy Model 5023
1975 Lawnboy Model 5024******1975 Lawnboy Model 5273******1976 Lawnboy Model 5274
1976 Lawnboy Model 8234EX****1977 Lawnboy Model 5024******1978 Lawnboy Model 5269G
1979 Lawnboy Model 7268******1980 Lawnboy Model 5247******1982 Lawnboy Model 5247
1982 Lawnboy Model 5247*******1972 Lawnboy Model 1015******1972 Lawnboy Model 1015
1987 Lawnboy Model 1400CL****1995 Lawnboy Model 61638

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Last edited by Yard Nazi; 07-05-2019 at 06:30 PM.
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post #7 of 17 Old 07-05-2019, 06:23 PM Thread Starter
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Here is the mower in question:
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post #8 of 17 Old 07-05-2019, 09:16 PM
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Re: Dumb lawn boy question

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Originally Posted by spokes100 View Post
a four cycle engine will tolerate having the fuel cut off because it is still being lubricated. a two cycle won't because the lubrication is the oil you mix with the fuel. shutting off the fuel lets the engine run lean and will prematurely wear out the piston, rings and bearings.
I tend to think the same way. Once a season is fine, but I donít think Iíd want to do that on a 2 stroke after every mowing. When I was a kid mowing lawns for money I used to mow until it ran out of gas. Knowing what I know now, I just would not do that with my Lawnboy 2 stroke. The same with a lean surge, itís about the same as straight gassing.
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post #9 of 17 Old 07-05-2019, 09:43 PM Thread Starter
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I appreciate all the feedback. Thats what I was worried about. I couldn't find an owners manual for anything similar online so I didn't really know the do's and dont's with lawn boy engines. I will just turn off the fuel shutoff after I shut it down, and only run it out before winter.


Another question, this mower came with pretty much every attachment made for it I believe, but instead of a mulching plug as I have seen on some, it just has a door to put in place of the bag, do these mowers mulch well with the proper blade and what-not?
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post #10 of 17 Old 07-05-2019, 10:05 PM
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Re: Dumb lawn boy question

My mix is a 32:1 on the oily side. I run the carb dry after every use on 7073. I hear what your saying though. Hmm.
The Walbro carb is pretty darn robust. And I do add MMO. Thank you
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post #11 of 17 Old 07-06-2019, 02:08 AM
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Re: Dumb lawn boy question

hello there
it not a bad practice to shut fuel when you are done toward the end of mowing it keeps carburetor clean
and does not leave any bad fuel beyond at all and to say shared this tip before learned
this from my grandfather who was a lawn-boy dealer who better then from a former lawn-boy dealer
he shared this tip with my father he used lawn-boy mowers for many years with problems and with me as well
from your lawn-boy friend Scott
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post #12 of 17 Old 07-10-2019, 11:13 AM
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Re: Dumb lawn boy question

On 4 cycles engines I would add stabil to tank before storage for winter. If you don't the ethanol in the gas will weaken all gaskets and fuel lines and you end up with micro trash in the carb. That will stop you in your tracks and you will have to rebuild the carb or at least flush it many times after replacing gaskets and fuel lines . I used to get by with doing nothing when I ran out of gas..just gas it up the next time but with the addition of ethanol to gas, it creates a mess. Just my 2 cents
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post #13 of 17 Old 07-12-2019, 12:13 AM
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Re: Dumb lawn boy question

You should use Stabil at 1 oz per gallon and store it with full tank. Turn any fuel valves off AFTER turning off engine.
You want to store carb wet with stabilized fuel.
When you (esp on 4 stoke with no oil) store carbs dry, the needle and seat is dry. The caustic gas that it has been sitting in makes it cry out even quicker if you let t get dry.
If you took a bunch of rubber seat seals and set them on a table on air. They would take a long time to dryrot. Soak them in gas for a long time then sit out...the rot quicker.
Do this every time you shut it down and it in weeks time if dries out up top at inlet seal...it deteriorates quicker than if you keep stabilized fuel in bowl and you wnd up replacing rubber seal sooner due to leaking carb or flooded crankcase.

Last edited by TobyU; 07-12-2019 at 12:59 AM.
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post #14 of 17 Old 07-12-2019, 02:45 AM
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Talking Re: Dumb lawn boy question

Keep in mind there is fuel stabilizer and then there is ethanol treatment. Number one is not necessarily number 2. For the record, I have run all my 2 cycle Lawnboys and Toro 2 cycle snowthrowers dry at the end of the season and have never had any issues. They all start one pull, two possibly, when coming out of hibernation. I do not, however, use ethanol fuel. Most of our stations only have the ethanol free in the 91 octane and while the higher octane serves no purpose on a lawnmower it does give the advantage of no ethanol. I go through about 8 gallons a month in the summer and winter varies. There is no problem with using a fuel stabilizer, especially if you are not going through a lot of fuel in a short time. If you are forced to use ethanol blend be sure to get ethanol treatment. I am sure that Stabil has both the regular fuel stabilizer as well as ethanol treatment. If you must store your equipment with fuel in it then stabilizer and/or ethanol treatment with stabilizer is a must and a full tank keeps moisture out. Bill

https://www.homedepot.com/p/Sta-Bil-...2288/204742880

1968 Lawnboy Model 3054******1973 Lawnboy Model 8231******1974 Lawnboy Model 5023
1975 Lawnboy Model 5024******1975 Lawnboy Model 5273******1976 Lawnboy Model 5274
1976 Lawnboy Model 8234EX****1977 Lawnboy Model 5024******1978 Lawnboy Model 5269G
1979 Lawnboy Model 7268******1980 Lawnboy Model 5247******1982 Lawnboy Model 5247
1982 Lawnboy Model 5247*******1972 Lawnboy Model 1015******1972 Lawnboy Model 1015
1987 Lawnboy Model 1400CL****1995 Lawnboy Model 61638

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 #15 of 17 Old 07-12-2019, 03:50 AM
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Re: Dumb lawn boy question

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Originally Posted by Yard Nazi View Post
Keep in mind there is fuel stabilizer and then there is ethanol treatment. Number one is not necessarily number 2. For the record, I have run all my 2 cycle Lawnboys and Toro 2 cycle snowthrowers dry at the end of the season and have never had any issues. They all start one pull, two possibly, when coming out of hibernation. I do not, however, use ethanol fuel. Most of our stations only have the ethanol free in the 91 octane and while the higher octane serves no purpose on a lawnmower it does give the advantage of no ethanol. I go through about 8 gallons a month in the summer and winter varies. There is no problem with using a fuel stabilizer, especially if you are not going through a lot of fuel in a short time. If you are forced to use ethanol blend be sure to get ethanol treatment. I am sure that Stabil has both the regular fuel stabilizer as well as ethanol treatment. If you must store your equipment with fuel in it then stabilizer and/or ethanol treatment with stabilizer is a must and a full tank keeps moisture out. Bill

https://www.homedepot.com/p/Sta-Bil-...2288/204742880
I think the ethanol treatment and the other stabils are just a waste. I have no issues with regular Stabil and all the gas I can get locally is 10% ethanol.

You won't have nearly any problems with dryrotting as I mentioned with 2 strokes as the oil keeps the rubber much better conditioned than a 4 cycle.

Mowers that used to go 10-13+ years until the rubber seats were cracked up and leaking are now doing it a few years sooner and I see more issued with leaking from people who say they always "run them dry".

I also explain to them that even when they die out they are not dry. There is a still a bit or fuel in the bottom of bowl that will evap and leave white powder or green residue behind and hopefully the deluge of fresh fuel the next season will be enough to dissolve everything and it run well but you never know. The top part that seals off and prevents your carb from overflowing and soaking air filter and leaking entire tank out of filling crankcase with gas IS dry after a couple of hours and that can start to crack up faster than if it was still in a fresh gas with a nice dose of stabilizer.

I tell all my customers (that I like) that the best way to do it is...
The last time you use the mower for the season-
DO NOT pour the old stale gas from your gas can into it.
Empty gas can (pour into car or elsewhere) and get a bottle of stabilizer.
Go to gas station. Pour 1 oz of Stabil for each gallon fuel into EMPTY can.
Pump gas into can.
Go home and fill mower with fuel.
Cut grass.
Fill mower again and it will probably start up fine next season.


The customers I don't like as much I just let them bring them in every year and charge them the same to clean out carb.
The ones I really don't like, I **** them off or tell them to buy electric (since I don't work on those) and hope they never contact me again.

If I have to I might fix it for free if they promise to never call me again.
It's like loaning some people money....best way to get rid of them.
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