John Deere stx38 revs way too high

[rw02kr43]

I have a John Deere stx38 yellow deck with the 12.5 Koehler engine. When I start it up, it revs very high. Doesn't matter if I have the throttle at idle or choke, it still just revs free. I have shut it off quickly as I'm afraid ill damage something. I can move the throttle and it makes no difference. What could be wrong?

Thanks
Jason

 

[pile81]

Its possible your throttle plate came off, if its not that then your governor grenaded or is somehow out of adjustment.....

 

[Ifixdit]

I have a John Deere stx38 yellow deck with the 12.5 Koehler engine. When I start it up, it revs very high. Doesn't matter if I have the throttle at idle or choke, it still just revs free. I have shut it off quickly as I'm afraid ill damage something. I can move the throttle and it makes no difference. What could be wrong?

Thanks
Jason

You need to look at the governor arm and see if there is an adjustment to be made. It's possible that the governor spring has come off as well. Start the mower and tie off or clamp the engine brake handle so you can adjust the governor while the engine is running. If it revs too high, push the governor lever one way or the other till you figure out which direction it needs to go to lower the governed speed. Once you figure out the proper direction its just a matter of figuring out how to keep it there. Some mowers have a screw or nut that you can loosen to adjust the governor arm. Others have a lever arm that has several holes in a row that you can move the governor spring into to raise or lower the speed. You may need to lightly stretch the governor spring to make a change or you could also cut out a link of the spring to make a change. One other option is to bend the governor spring bracket one direction or another to achieve the desired result. Sure hope this helps. Good luck!

 

[rw02kr43]

I can move the throttle and the linkage moves. It moves 2 arms at the end. I don't know much about these engines. What should I be looking for? Is it also possible that the carb is stuck open somehow?

Jason

 

[pile81]

Just said above throttle plate could have came off that would make you run full throttle all the time........if its not that possibly governor out of adjustment some how, or it shelled inside the engine

 

[rw02kr43]

Well it took it apart today. The plate on the inside closest to the engine seems to move freely independent of the arm on the top. The side with what I believe is the choke plate has a spring on top. The throttle side doesn't. Should it? I also see a flange on the side with the starter. It looks the same as for the carb or for a muffler. It has nothing going to it though. Sould it? So, can the dealer sell me a throttle plate and spring if its needed? Or can I repair the one I have? I tightened the screws on the plate and it made no difference.

Thanks
Jason

 

[BBO]

So, can the dealer sell me a throttle plate and spring if its needed?

Does it look like this?


If you are missing a spring you need to order it.