New 21" Craftsman Mower

[MolaKule]

I bought this mower about a month ago and had my grandboys mow my yard but when it got hot it would be hard to start unless I removed the air filter. In addition, gas would ignite in the muffler indicating too much fuel was being fed in.

Removing the fan cover I found this link from the carb choke (lower right) to a Thermostat (lower left). I spread out the link to allow less choke and now it starts up when very hot. This engine is a B&S 093J00. I suspect this choke will be a problem child in the future. I also removed the spark plug to check the gap and it was about 0.0215" just slightly over the spec of 0.02."

 

[Wrenchturner44]

Did it come with fan shroud cover?

 

[MolaKule]

The rest of the story is explained above.

 

[Cujet]

Who knows, maybe the wax bulb (or what ever it is) will be reliable. It will probably work perfectly, now that it is adjusted correctly.

 

[CharlieJ]

I had a nearly identical front wheel drive Yard Machines brand of that mower. I added an inline fuel filter and bent the governor "rod" to increase the engine RPM to 3700. It worked great at that speed!

 

[MolaKule]

Who knows, maybe the wax bulb (or what ever it is) will be reliable. It will probably work perfectly, now that it is adjusted correctly.

True, it is a coiled spring thermostat that is loosey-goosey and mounted on the muffler mounting bracket. I assume thermal conduction from the muffler heats it up and opens up the choke as temps rise.

 

[xgmad]

True, it is a coiled spring thermostat that is loosey-goosey and mounted on the muffler mounting bracket. I assume thermal conduction from the muffler heats it up and opens up the choke as temps rise.

I deleted the "ready start" (the thermostat) and replaced the carb with a manual choke and speed lever carb because after a couple years these things just start sticking and stop working right.

 

[Gyro Gearloose]

I don't know what the official choke adjustment procedure is but I had one that was too tight as well causing an overspeed when starting cold. Setting the choke to be closed with just a slight amount of tension at 60-70 degrees ambient seems to work well. I have an older Briggs that the thermostatic choke has worked great for 12 years with no issues so I think it is a pretty well executed design if set up right initially.

 

[blufeb95]

I have an older Briggs that the thermostatic choke has worked great for 12 years with no issues so I think it is a pretty well executed design if set up right initially.

Is it strictly a thermostatic choke or is it one of those hybrid air vane and thermostatic deals?

 

[MolaKule]

Is it strictly a thermostatic choke or is it one of those hybrid air vane and thermostatic deals?

The choke itself appears to be a coiled spring thermostatic choke. There is also an air vane control, so it could be a combination system.

 

[blufeb95]

The choke itself appears to be a coiled spring thermostatic choke. There is also an air vane control, so it could be a combination system.

I know on the new smaller OHV engines from the last 10 years like you have they only have a thermostat, but 12 years ago would've likely been a flathead, and the autochoke setup on the Briggs Quantum I'm familiar with uses an air vane choke at cold start and then has a thermostat that forces the air vane to stay back for easy warm starting. Although I guess they were putting the 190cc Intek on some mowers 12 years ago, i don't know how the Intek auto choke is configured.

 

[MolaKule]

I know on the new smaller OHV engines from the last 10 years like you have they only have a thermostat, but 12 years ago would've likely been a flathead, and the autochoke setup on the Briggs Quantum I'm familiar with uses an air vane choke at cold start and then has a thermostat that forces the air vane to stay back for easy warm starting. Although I guess they were putting the 190cc Intek on some mowers 12 years ago, i don't know how the Intek auto choke is configured.

Just to clarify, the air vane control and the thermostat control are two independent and separate carb controls and one does not control the other.

 

[blufeb95]

Just to clarify, the air vane control and the thermostat control are two independent and separate carb controls and one does not control the other.

On some older smaller flatheads I've seen the air vane used as a throttle governor, but on the bigger Quantum flathead they use an air vane setup on the choke, the air vane is really there to help as the engine warms up and gets up to full speed and will remain pushed back if the engine remains at full speed and doesn't lean surge, but if the engine is warm the air vane choke alone would likely flood the engine and it'd be a bear to start, so the thermostat is there to hold the air vane in the full speed position to make warm starting easier.

 

[MolaKule]

On some older smaller flatheads I've seen the air vane used as a throttle governor, but on the bigger Quantum flathead they use an air vane setup on the choke, the air vane is really there to help as the engine warms up and gets up to full speed and will remain pushed back if the engine remains at full speed and doesn't lean surge, but if the engine is warm the air vane choke alone would likely flood the engine and it'd be a bear to start, so the thermostat is there to hold the air vane in the full speed position to make warm starting easier.

Understood, but here on this carb this does not seem to be the case.

 

[Gyro Gearloose]

Its hard to tell from this picture but the OHV engines like this one have a cam on the throttle shaft linkage that pushes on the choke shaft linkage and forces the choke open as the governor begins closing the throttle. All the cam and lever parts are just part of the carb design so Briggs gets to cut one part off the engine - the air vane. The new system seems to work just as well as the air vane as long as the spring tension from the thermostat isn't excessive.