21" 6.75hp Walk behind mower running a little weak after cleaning the carb

[MD56]

Hi All,

A little info on the mower.

Troy-Bilt 21" 6.75hp - walk behind mower (model: 11a-436n211)

Motor: Briggs & Stratton 126L02-0675-F2 (auto choke)


So I picked this mower up for free on CL about a year ago. The owner said it wasn't running and he didn't care to figure out why. Well, a can of carb cleaner later I had it running like brand new.

So a couple of weeks ago it started giving me fits. It would run poorly and then just stopped starting all together. This weekend I pulled the carb, took it apart, cleaned it thoroughly and put it back on. The mower fired right up, and is running very smooth. But for some reason it's running a little weaker than it usually does. The RPM's seem down and I notice the motor get's bogged down easier when I run through a trick patch of grass.

I popped the fuel life off and confirmed that fuel is flowing normally. I also checked the air cleaner, it's dirty but not so much that i think it's restricting air flow.

Any advice on what might be causing the power loss?

 

[LazerZLandscaping]

Is the mower running lean? What type of fuel do you run in it? If you run anything over 10% ethanol, or you run E85, E15, etc, don't run that at all through any mower. Causes damage and power loss. I run 93 octane in my mowers with a little bit of octane booster, and they run like a top. But you can also just get normal 87,89,91 unleaded fuel and just buy some octane booster to add to the gas can. Also, check your spark plug and clean it or replace it with a new one.

 

[Wildcat]

I had a push mower do the same thing the other day. At first I thought it was a fuel issue. I went on with my day using it while it sputtered and almost dieing every push. I got tired of it and took off the air filter and check the carb. I pushed the primer a few times and it worked, then I started it without the air filter on. I've haven't heard the motor sound that strong in a long time. So I pulled the air filter out of its housing and just as yours, it doesn't look that dirty. But I guess its dirty enough to restrict air flow. Now I have replaced it and the mower is running strong.

My advice is to run it without the air filter and go from there.

 

[LazerZLandscaping]

I had a push mower do the same thing the other day. At first I thought it was a fuel issue. I went on with my day using it while it sputtered and almost dieing every push. I got tired of it and took off the air filter and check the carb. I pushed the primer a few times and it worked, then I started it without the air filter on. I've haven't heard the motor sound that strong in a long time. So I pulled the air filter out of its housing and just as yours, it doesn't look that dirty. But I guess its dirty enough to restrict air flow. Now I have replaced it and the mower is running strong.

My advice is to run it without the air filter and go from there.

I'll have to see if this will work for the Bolens that will be retired.

 

[MD56]

Thank's for the replies everyone.

As far as gas goes, I run the same E85 in it that I've always run, never had a problem before I started having problems lol.

So regarding the air filter, it actually runs worse when I pull the filter. When I fire it up without one it start to chug and sputter a little every couple of seconds. When I fit the filter back in, it levels out and runs smooth but definitely still weak. I've ordered a emplacement filter anyway though just to check it off the list. For all I know though you could be 100% right, we'll see!

I was thinking that maybe bracket that attaches to the throttle body spring might have gotten a little tweaked or something last time I messed it with. I was watching a few videos on B&S repair and one of the suggestions for boosting the RPM's was to bend the tab out a little bit that attaches to that spring. I guess to put more tension on the spring thus opening the throttle body a little more.

Also, regarding running lean / rich... my carb does not have any mixture screws or an idle adjustment, how could it just starting running lean all of a sudden?

At any rate, i've ordered a bunch of replacement parts:
Air Vane spring / arm
Throttle body spring
Fuel filter
Air Filter
Carb gasket

They were all cheap and hopefully in replacing all of these it will take care of the issue. I'm looking forward to having my nice strong mower back hopefully!

 

[LazerZLandscaping]

Thank's for the replies everyone.

As far as gas goes, I run the same E85 in it that I've always run, never had a problem before I started having problems lol.

So regarding the air filter, it actually runs worse when I pull the filter. When I fire it up without one it start to chug and sputter a little every couple of seconds. When I fit the filter back in, it levels out and runs smooth but definitely still weak. I've ordered a emplacement filter anyway though just to check it off the list. For all I know though you could be 100% right, we'll see!

I was thinking that maybe bracket that attaches to the throttle body spring might have gotten a little tweaked or something last time I messed it with. I was watching a few videos on B&S repair and one of the suggestions for boosting the RPM's was to bend the tab out a little bit that attaches to that spring. I guess to put more tension on the spring thus opening the throttle body a little more.

Also, regarding running lean / rich... my carb does not have any mixture screws or an idle adjustment, how could it just starting running lean all of a sudden?

At any rate, i've ordered a bunch of replacement parts:
Air Vane spring / arm
Throttle body spring
Fuel filter
Air Filter
Carb gasket

They were all cheap and hopefully in replacing all of these it will take care of the issue. I'm looking forward to having my nice strong mower back hopefully!

If your mower is newer, the EPA sets these dumb standards and they install these newer redesigned carburators that are designed to run lean for 'less smog', or other stupid things like that.

On a side note, NEVER run E85 in a mower, causes damage. Always run E10 or less in power equipment.

 

[Wildcat]

Unless your manual states you can run E85, don't do it. I don't even like getting gas that has 10% in it so I go a few more miles out of the way to ensure that.

As for your parts list, its a good start and I hope it fixes your problem.

Good luck.

 

[MD56]

Unless your manual states you can run E85, don't do it. I don't even like getting gas that has 10% in it so I go a few more miles out of the way to ensure that.

As for your parts list, its a good start and I hope it fixes your problem.

Good luck.

i could be wrong about this, but in California I don't think we have a choice. Our gas here sucks.

 

[LazerZLandscaping]

i could be wrong about this, but in California I don't think we have a choice. Our gas here sucks.

Yeah, you don't have a choice. California gas sucks. But mowers sold in CA I believe are exclusively 'California Models', only sold in CA. The motors were built to stand California gas.