Simplicity Sunstar Puzzle

9n200460

New User
I am trying to fix a Sunstar hydro with the Kohler 20 Magnum engine. It idles well and runs okay when I put a load on the engine by engaging the mower deck. But when I move the transmission control forward or back it runs bad, like it is loading up. I did a carb clean/rebuild and changed out the ignition module with one I believe is good from an old Sunstar. I also replaced the hydraulic fluid and filter. Any ideas as to why it runs okay with the deck on but not when just trying to engage the hydro drive?
 
If you open the release valve so the tractor will
roll, will it roll? Will the control then move
forward and back without loading the engine? If so,
sounds like something is locking the output of the
hydro. Is there a park brake? Is it actually
releasing when the lever is moved? Could something
be wrapped around the axle? Check for anything
external, if nothing found, there is something
locking it from the inside.
 
I put the lever in the middle neutral position and it does roll freely. Then I started the engine and when I moved the speed control lever out of neutral,at first it ran okay but then would run rough almost every time it is moved to the right. It runs rough when I move the speed control forward or backward from the center position. Although it was in neutral, it moves in either direction when you move the lever up/down Should it be doing that?
 
Try jumper wiring the seat sensor. It may be trying to shut the motor down because the neutral safety switch disengages when you move the lever and the seat switch could be faulty.
 
I disconnected the rod from the speed control lever to the transmission to rule out anything with the hydrostatic drive and the problem did not go away. I then replaced the dual interlock switch under the dash that the speed control lever presses against when it is in neutral with one from a donor tractor. It now runs fine in neutral, forward and backwards. Thanks to all for helping me rule other possible causes.
 

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