Scag SSZ CV22 won't engage mower deck

Hello. My old (1996 vintage) Scag SSZ CV22 (22 HP Kohler twin) 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:

https://www.youtube.com/watch?v=FlxhzQnLlY

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

 

Two problems you list are not problems (1)"Once running, applying full choke kills the engine." This condition will kill any engine. (2)"With the belts removed, engaging the deck switch has almost no effect on the engine." This condition has no affect on engine operation. My guess is the governor linkage has been distorted or governor spring has lost its tension. It is important to get a spring from a reputable source as the length and spring rate must be correct for the governor to operate properly.

 

Could be the governor or you could have one cylinder not doing its job. Try pulling plug wires one side at a time to check for a weak cylinder. The video isn't coming up, but the shaking you've mentioned could be an indication one side is lame..

 

If you find one side isn't firing, check for spark on that side and if no spark, let us know, it may be either a bad coil or diode. The latter turns up here a lot.

 

I can't see how to edit my initial response, here's the full video link:

https://www.youtube.com/watch?v=FlxhzQnLlYQ

 

The link works now. The engine sounds pretty normal. Can you post a video of the engine running at idle and progressing to high rpms? The idler shaking in itself isn't your problem.

 

Once I get home from work I intend to work on it. I'll shoot some more video then.

 

Took a video of a cold start. Typical of how it usually starts:

• First try gets nothing, just a click.
• Second try, choke in, nothing.
• Third try, choke out, a few sputters.
• Fourth try, choke out, a couple of sputters.
• Fifth try it sputters to life.

It's a bit tough to start, but seems to run fine once started. It's typical that I need to try choke in or out before it will start. Generally runs smooth, no real vibration. Really doesn't seem to be running one on cylinder, but I haven't tried pulling plug wires yet. I wanted to get this uploaded, I'm heading back out to fiddle with it.

https://www.youtube.com/watch?v=koUlMiWpWyI

 

Pulled the LH plug wire and tried to start it. Nothing. Replaced it.

Pulled the RH plug wire and it started and ran almost exactly like the video.

So the RH cylinder isn't firing. Probably a bad coil or diode then.

 

Yep, or at least headed in that direction. You need to find the kill wires coming off the coils and disconnect those from the kill harness. Keep in mind you'll have no way to kill the engine when started and you'll have to choke it to shut it down.

Dis connect those coil kill wires between the coils and the wire juncture to the main harness. Then try to start it. If it runs well, the diode is probably bad or the kill wire harness is grounding between the coil and the wire juncture of the two coil kill wires. The most common thing that shows up here is the diode.

However, if with the kill wires disconnected, you still have a lame engine, check the RH coil for spark. If no spark, replace the coil.

 

I don't think this has traditional coils. I need to look it up but I believe it has the Kohler Smart Spark or something like that. Not sure if it has diodes or not. It's a CV22S, spec number 67509,family SKH624U1G2RB according to the engine label.

Unless they're crazy expensive, I plan on replacing both coils / ignition modules, plugs and, if applicable, the diode. It's 20+ years old and I'd like to get several more years out of it.

 

Mice.

That's my issue. Under the engine cover was a lot of nesting material and this:



Note the broken plug wire plus the two other stripped and frayed wires. Before that picture was taken the area to the right of the cylinder was packed with grass and ... stuff. I hate mice. And I even have two cats, but no cat door into the shed where the mower is stored. That will change.

So, a new ignition module is needed.

Also, I pulled the non-working plug and, aside from being wet with fuel, it looked good.

 

Yep, that plug wire should be hooked onto something, I'm pretty sure.

That ignition system would have some type of variable timing, but we'd need Cheese to weigh in on it as far as diodes. The extra hardware for the timing may separate the kills on the way to the switch. If not you would need a diode.

But it looks like a new coil may take care of everything. And a mouse only does one plug wire in it's lifetime. You're home free

 

While a mouse may have finished the job, it appears the wire insulation cracked from an excessive bend and vibration as it exited the ignition module. Maybe there is a wire clip missing. Check with a dealer if nearby.

 

Looks like you found the problem. A new coil module should get it back on track. This type of system with the SAM module doesn't have the diodes in the kill wires. You'll need to grab some butt connectors and repair those bare wires too.

 

Got the new ignition module installed and now it won't start. Cranked for a bit tried to fire and stopped immediately like it was locked up. Cranked again with the same results and now it won't crank at all. Not a click, nothing. I did verify that I can turn it by handI put it on the battery charger, I'll try it again later.

I had a mouse issues a couple of years ago too (no wire damage that time) and it did the same thing. I ended pulling the cover again, poking around underneath but not really changing anything and putting it back together and then it started and ran fine since.

 

The wire from the starter switch to the starter seems loose at the starter (spade connector). I wiggled it and got it to crank again, but it did not fire. Won't crank anymore, regardless of the amount of wiggling. It's been spliced several times, I think I might just replace it. This feels like a separate, bad connection issue. As you can see in my second video, it sometimes will only click and not start and has done that for some time. I think I'll clean the connections at each end of the battery cables too.

But, family is arriving soon for the Easter weekend in 30-45 minutes so it'll have to wait. It's too wet to mow now anyway.

Now, if I could only stop the grass from growing ...

 

The coil fixed my deck engagement issue, but I've still got a problem with the wiring. It cuts out and won't restart easily randomly. I started a new thread on that here if anyone has any ideas.