Monday, August 7, 2017

Kohler SV730 V-Twin Ignition Adventure

This may not be an engineering article, but maybe it will be helpful to someone else with this issue.

I started my lawnmower, and backed it partway out the garage, when the engine died. That's strange, I thought. It never did that before. It restarted right up. It ran okay, but it sounded funny. Like a one-cylinder lawnmower engine, except this is a V-twin. A miss doesn't sound too bad on a two cylinder engine, if it's a consistent miss.

I drove it out on my driveway, popped the hood, and pulled off the left spark plug wire. The engine kept running like nothing happened. The sound was the same, and the RPM didn't change. So I put the left spark plug wire back on, and pulled the right one. Bam! The engine died instantly.

Okay, so maybe we have a bad spark plug. I removed the left one. It looked pretty good, but it was a bit moist with raw gas. Consistent with no spark. So I swapped it out with the right side, and restarted the engine. Same thing. When I pulled off the right spark wire, the engine died. The problem stayed with the cylinder; it didn't follow the spark plug.

Now I'm worried, because I don't want a major engine failure here. I hope it's something simple (and inexpensive). I pulled the left spark plug out, connected the spark wire, held the plug against the cylinder head and cranked the engine. No spark. I did the same thing on the other side. Spark. Well, something's wrong with the left side ignition. What? I could have been shocked or injured? Back off, I'm a trained engineer!

To find out what I'm dealing with, I pull off the blower shroud -- something I've never done before on this engine. There are two little electronic ignition modules under there. They're held on by two bolts each, and they look identical. So I unplugged the wiring harness from each one, and swapped them, left for right. Then I put it all back together and restarted the engine. See if you can guess what happened.

That's right, it was still only hitting on one cylinder, but now the left cylinder was the good side. One of the ignition modules had gone bad.

Kohler MDI Conversion Kit
So, for the first time in all of this, I dug up the service manual and looked up the part number. I got online, and found several places that carry the part. This is where it gets interesting (in case it wasn't interesting up until now). The part pictured doesn't look anything like the part I was holding in my hand. Furthermore, they are only available in pairs, and the description is "MDI conversion kit". (MDI := Magneto Digital Ignition -- what makes it digital?)

Kohler DSAI Module
It seems the part in my hand is a variable timing ignition module (DSAI := Digital Speed Advance Ignition) that advances the spark at higher RPMs. But they have been fraught with problems, and after several revisions, Kohler finally discontinued them. After much research, I finally found the tech bulletin where they describe the problem. I can't tell if the conversion kit still features a spark advance, or how much difference it makes to have a spark advance. At $100.00, I don't consider this an inexpensive fix, but it could have been worse.

I've always loved this engine, so I hope it runs as well with the conversion kit, as it did before. I also hope the parts get here before Saturday, so I can mow next week. My yard looks awful.

So, how was your Saturday?