Hello. My old (1996 vintage) Scag SSZ CV22 with a 61" deck won't stay running when I engage the mower deck. Here are the symptoms:

  • Starts and runs OK, but doesn't want to run with the choke on. I need to push the choke in right away to keep it running.
  • Once running, applying full choke kills the engine
  • When I engage the mower deck the main idler shakes quite a lot and it kills the engine.
  • If I apply part choke I can get it to stay running with the deck engaged, but it won't run full speed.
  • With the belts removed, engaging the deck switch has almost no effect on the engine.
  • With the belts removed all 3 blades turn freely by hand with no discernible difference in friction and no noises.
  • Each idler turns very freely but each has a fair bit of vertical play, especially the main idler.
  • Belts were replaced last season when the mower was thowing the main belt while mowing. After replacing the belts it ran fine for the rest of the season.

Here's a video of the belts when I try to engage the deck:

I'm a pretty handy DIY guy, but not sure where to go from here. What should I check next?