WxService Update Available

WxService ow4j171209

• Modified WxMonitor wind vector display to clean up a problem I've had since day one with 'crawly' wind direction display. The problem is, even when I retain precision and round properly, trying to display a short direction indicator line on the outer circle, the graphics resolution simply isn't good enough to draw a line with the proper slope and length. When I draw a line at the full radius, the problem goes away, because the resolution error is spread out along the full length of the line, instead of a short line segment. This is easiest to visualize if you imagine a two-pixel length line. The length and slope errors become overwhelming. When the line is thousands of pixels long, the length and slope errors are usually negligible. 
• Changed the way WxMonitor displays UI updates. The monitor will now 'animate' each sensor update, instead of coalescing them. This improves the behavior for historical markers, such as the wind vector memory. It is also entertaining to watch the last 12 hours of data being animated when first starting WxMonitor. 
• Modified the default command line behavior. The backlog default is now set to 12-hours, and the polling interval default is 5 seconds. If these values are acceptable to you, there's no need to specify anything on the startup command except for which weather server you want to connect to.

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WxService Update Available

WxService ow4j171123

• Simplified sensor data module, and moved domain-specific 'timeout' into the Weather Underground formatter, where it is actually needed. Basically code cleanup. 

This change will not affect normal operation of anyone's weather station; I just wanted to do some code maintenance. 

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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?