Craftsman riding mower engine speed problem

[tylertown]

My 2009, 21hp craftsman riding mower with B&S engine only runs at half throttle immediately after start up even though control is set at full throttle. After cutting about 1/3 acre, the engine speed begins to increase until it finally runs at full throttle. At first I could move control from full throttle to half with no engine speed change so I thought it might be a fuel flow problem. I have changed the fuel filter, spark plug, checked air cleaner, put in fresh fuel, and inspected for any debris under the engine cover with no affect.
I would appreciate any advice anyone might have.

 

[chance123]

Sounds like your governor lever or linkage is binding. With the engine off, see if this lever/linkage is free moving

 

[tylertown]

Thanks. I had noted that I could not move the governor lever with the engine not running but didn't know whether this was normal or not. I checked it again today and got the same result. It wasn't just binding, it could not be moved at all with a decent amount of pressure on it. I doused the shaft area where it comes out of the engine with WD40 and will try it next week when I cut my grass. I will also check it after it seems to be running correctly.

BTW the engine is a model # 331877 type # 1234-B1.

 

[chance123]

when you attempt to move the governor lever, move your throttle to the slowest speed. This will relax the governor tension spring, and it "should" move freely. It won't move much, only enough to move the carb butterfly to full open and closed. If it won't move at all, it has to be determined why it won't move. It could be simply a dirty/gumed up throttle shaft on the carb. These often get dirty, because if you should have a dirty air filter for example, the engine will try to get more air from anywhere it can, and the next path of least resistance is through the small clearence around the throttle shaft. I have seen many shafts and carb bodies completely worn out to the point where the whole carb must be replaced.

 

[tylertown]

My thanks to you again!! I just went out and checked it again. With the control at low speed, the arm moved easily 1/4" to 1/2" either way. i don't know if the WD 40 loosened it or not but I started the mower and engaged the blade and everything seemed to work normally.
The mower was used yesterday so I am looking forward to seeing if it works properly when I mow next week.

 

[chance123]

Yes, when the throttle is in the fast position, the governor arm is hard to move because the governor spring is pulling on it.