Husqvarna lc121p with B&S 725EXi engine low power.

[WaltDisney]

The backing on the left is for auto choke models, not sure about the one on the right. Maybe it's for a primer bulb type system?

The one on the right was the original A.F. plate, which the mower didn't use a primer, but an autochoke system. The one on the left was from a similar mower that also had an autochoke on it too, so I just swapped the original plate for the extra one off the similar mower. Could that explain the constantly low power with the original plate? With the "new" plate on there is only low power at start up due to the autochoke still being closed, thus leading to a rich mixture at first, but eventually leaning out once the choke is fully opened.

 

[Auto Doc's]

The air vane near the flywheel and a small spring are supposed to reduce the choke fairly quickly as the thermostat on the muffler heats up. It's an over engineered system. It's been a long time since B&S made anything simple and DIY friendly.

The linkage can be a bit confusing, so check out a couple of videos online.

 

[WaltDisney]

The air vane near the flywheel and a small spring are supposed to reduce the choke fairly quickly as the thermostat on the muffler heats up. It's an over engineered system. It's been a long time since B&S made anything simple and DIY friendly.

The linkage can be a bit confusing, so check out a couple of videos online.

I've seen a few videos explaining how the pneumatic autochoke works, however, this model of mower only has a thermostatically operated autochoke, so it sadly does take a bit longer for the choke to fully open from a cold start as it takes time for the muffler to heat up.

 

[Auto Doc's]

This is why it is important to verify the air vane is functioning properly. This give the thermostat time to heat up and hold the choke open. The choke initially is held open by the air vane operation.

 

[WaltDisney]

This model of mower doesn't have an air vane on it, so it is only relying on the thermostat to heat up to open the choke.

 

[Auto Doc's]

Thanks for the update info. The only other thing left I can think of at the moment is a possible aftermarket air cleaner that is blocking proper air flow.

 

[WaltDisney]

The air filter is OEM and the correct filter for the model according to the parts diagram. I'm starting to think the verdict is that the low power at start up is an inherent part of the mower until the muffler heats up enough to fully open the choke.

 

[andrewslarge]

The air filter is OEM and the correct filter for the model according to the parts diagram. I'm starting to think the verdict is that the low power at start up is an inherent part of the mower until the muffler heats up enough to fully open the choke.

That has been my experience. It coughs black smoke a bit on startup and then smooths out some time. I’ve had mine fail to start it it ran for just a minute, I shut it off to adjust something, and then tried to start it. The engine had time to warm up and the restart needed a choke .

Shot of starter fluid and I’m off!

 

[WaltDisney]

That has been my experience. It coughs black smoke a bit on startup and then smooths out some time. I’ve had mine fail to start it it ran for just a minute, I shut it off to adjust something, and then tried to start it. The engine had time to warm up and the restart needed a choke .

Shot of starter fluid and I’m off!

So I'm not the only one who's having that same thing happen on a thermostatic choke mower? Is this a known thing with some mowers?

 

[andrewslarge]

So I'm not the only one who's having that same thing happen on a thermostatic choke mower? Is this a known thing with some mowers?

It has happened with me. The carburetor is a good design. I have had to drop the bowl, clean the main jet, install a new bowl gasket.

The choke is interesting.

One it’s running correctly I just keep it filled with fuel and mow.

I did add a fuel cutoff to my fuel line.

My shutdown process is to shut off fuel and let it run til it stops.

My startup process is to check oil, fill with fuel from a sealed can, check the air filter, turn on fuel valve, and then pull start. It usually starts on the first or second pull.