Engine Engine starts sometimes, but does not run smooth; revs up and down

wzahpnn

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  • / Engine starts sometimes, but does not run smooth; revs up and down
Hi! Mower engine problem.
First post here after reading all the posts in the Weed Eater forum and not finding a solution. I picked up a used Weed Eater One 875 series (WE261) Riding Lawn Mower with a Briggs & Stratton engine model # 12S907-1411 B1. It starts occasionally with the pull start (I will troubleshoot electric start later as the battery only had 11V on it), but after I run it for a while and shut it off, most times, it won't start up again. The engine doesn't run smooth either. You can hear the RPMs go up and down every second or so. I can ride it around and mow the lawn, but don't like that it won't start up again sometimes after running, and doesn't run smooth.
I replaced the carburetor and still have the same results. When I hold the throttle open all the way, it runs/sounds pretty good, but of course, it won't stay that way unless I hold it. I have also replaced the spark plug, air filter, and put new fuel in after replacing the carb. Looking forward to your advice and finding a solution! : )
One additional note, I can pull start it and run it for a 30 seconds or so, shut it off, and then pull start it again and it will usually start.
AL
 
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bertsmobile1

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  • / Engine starts sometimes, but does not run smooth; revs up and down
Take the blower housing off and clean out all of the cooling fins, remove any debris in there.
While you are there, set the valve lash 0.004" both sides.
When running check the voltage at the battery is if is less than 13 V you have a charging problem.
The thing under the carb is a shut down solenoid that closes the fuel supply to the engine .
Some of them are sensitive to voltage so will shut down when volts drop below 10V.
A duff battery & alternator will run down very slowly while you are mowing .
When the mower sits for a long time, the battery equalizes and the voltage rises slightly, just enough to open the solenoid when you turn the key.
 

wzahpnn

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  • / Engine starts sometimes, but does not run smooth; revs up and down
Take the blower housing off and clean out all of the cooling fins, remove any debris in there.
While you are there, set the valve lash 0.004" both sides.
When running check the voltage at the battery is if is less than 13 V you have a charging problem.
The thing under the carb is a shut down solenoid that closes the fuel supply to the engine .
Some of them are sensitive to voltage so will shut down when volts drop below 10V.
A duff battery & alternator will run down very slowly while you are mowing .
When the mower sits for a long time, the battery equalizes and the voltage rises slightly, just enough to open the solenoid when you turn the key.

Hi and thanks for your advice. I've cleaned the cooling fins. I do not know how to "set the valve lash to .004" on both sides" (any instructions available somewhere?). I checked the voltage at battery while running and it stays the same as when the engine is off (11.4V), so yes, I must have a charging problem and will troubleshoot that too. I will have to review the engine parts list and see if I can find the "shut down solenoid" as I looked under the carb and didn't see anything.
 

bertsmobile1

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  • / Engine starts sometimes, but does not run smooth; revs up and down
You might not have one, but we do not know that because you have not told us what engine is in there.
Weedeater was a low end product usually fitted with the cheapest Tecumseh engine sold through department stores.
Some of them predate the EPA manditory carb solenoid, but again we do not know this.
Weedeater was a brand name applied to budget ride ons to cash in on the popularity of the trimmers.
Weedeater quickly went down the gurgler & got taken over by Frigidaire who ultimately sold the brand name to Electrolux and it eventually became part of Husqvarna
Thus there is no service information currently available for Weedeater mowers
So we only know what you tell us.
Some parts retailers have legacy parts lists still on line but again without the exact information from the ID tag under the seat and the model numbers from the engine we have little idea about what you have.

Down here we got a lot of them fitted with obsolete 8Hp side valve engines.
 

wzahpnn

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  • / Engine starts sometimes, but does not run smooth; revs up and down
You might not have one, but we do not know that because you have not told us what engine is in there.
Weedeater was a low end product usually fitted with the cheapest Tecumseh engine sold through department stores.
Some of them predate the EPA manditory carb solenoid, but again we do not know this.
Weedeater was a brand name applied to budget ride ons to cash in on the popularity of the trimmers.
Weedeater quickly went down the gurgler & got taken over by Frigidaire who ultimately sold the brand name to Electrolux and it eventually became part of Husqvarna
Thus there is no service information currently available for Weedeater mowers
So we only know what you tell us.
Some parts retailers have legacy parts lists still on line but again without the exact information from the ID tag under the seat and the model numbers from the engine we have little idea about what you have.

Down here we got a lot of them fitted with obsolete 8Hp side valve engines.

I listed the model number (12S907-1411 B1) of the B&S engine and the series (875) in the original post. What other info would you like about the engine? It also says 190cc. The Weed Eater lawnmower model number under the seat is 960260002 and then WELRV1. Do you happen to know how to troubleshoot the alternator on this model engine? I had taken it off to look at it, but didn't note the gap before I removed it. How close to the fins should it be mounted? Also, I just looked up the alternator's output and it says it is supposed to be .5 amp regulated DC
 
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bertsmobile1

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  • / Engine starts sometimes, but does not run smooth; revs up and down
:ashamed::ashamed::ashamed::ashamed:
Must need new specs sorry about that.
Pull the fuel tank off and clean it out.
Pull the blower housing off and check the timing key.
Both side of the holes should line up to make a perfect square.
Pull the rocker cover off & adjust the valve lash to 0.004".
If it has one of the metal encased spark plug caps you would be advised to remove it & fit a rubber one as the steel ones have a habit of grounding the spark.

Those little engines are really overworked cutting 30" plus hauling the owner & mower around the yard.
And for some strange reason they seem to be favoured by owners at the very large end of the weight scale who think it is a bush hog.

AFAIK both the magneto & alternator coils are set at 0.010" from the magnets.
The alternator is very small because there is no power to spare from the engine to recharge the battery.
The pulsed DC power supply tends to fry batteries and you would be advised to keep the battery on a battery tender and use a jump pack if you are going to use the starter motor
 

wzahpnn

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  • / Engine starts sometimes, but does not run smooth; revs up and down
Thanks Bert! Lots of things for me to look up on how to do, but I will get on it!
 
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