Things that make ya go HUH?

Every now and then you run into a problem that defies common sense. It also seems to occur most often with the simplest of things. Recently I had a PW50 kick my butt over a no spark issue. How in the world can such a thing happen? I had a few nights of cognitive dissonance over an electrical system that didn't function correctly and there are only a switch, a coil, a pickup coil, a charge coil, a control unit, CDI unit and the spark plug.

The owner had taken it to another shop and was told it had a bad generator. $200.00 plus labor to fix. Labor was quoted at "a couple of hours". I don't know what that was, but it was probably going to cost at least $300.00 after taxes. They spent $100.00 for the bike. OK it wasn't a cream puff. It's missing the airbox, both fork tubes are bent and the rims wobble a bit. Hey! its a Christmas present for a little kid. If someone had given it to me at his age I would have treated it like a new Aprilla V four.

I first checked the "generator" more accurately an AC Magneto and it was putting out voltage and the pulse coil ohm'd out good. So much for the bad "generator" theory. Next I ohm'd the ignition coil and it checked good. Tried a new plug, still no spark! Checked all the wire connections, all good. PW50's have a unique switch on the throttle side. It has a Start, Run and Stop setting. The purpose is so little Johnny or Mary doesn't pin the throttle and wheelie off into oblivion. First it starts and then you switch it to run and off they go. The stop position is obvious. PW's also have a control unit. It's unclear what it does and the service manual from Yamaha doesn't help clear up it's function either. I know that it has five wires and they need to be checked.

Luckily, I have a good relationship with the local Yamaha dealer and they loaned me a Genuine Yamaha service manual. Armed with the manual I check the control unit. According to the service manual I should have an infinity reading on the W/R wire from positive across the other four wires. I have infinity reading on the W/R wire from negative across the other four wires. The plot thickens!

Go home for the night and read the service manual section on electrical system is my next plan of attack. After reading the section on ignition I realize that I am missing some point. I don't know what it is, but I am sure that I am missing it.

Next morning I decide to start from scratch. I follow the service manual step by step and get the same readings on every step that I had gotten before. The pulse coil checks good in both ohms and output. The charge coil has the same results. The ignition coil checks good on both primary and secondary circuits. All wire connections are good. All wires have continuity. (Thank you for only having a few wires) The handlebar switch has the right connections in all the right positions. The control unit still is basakwards. And there is no check for the CDI. "Replace unit with one of known value to evaluate." Great advice unless you don't happen to have another one.

Now here is the dilemma. I know that something is bad...but what? The control unit is backwards and there is no check for the CDI. Are both bad? Is one bad? Which one? I need a drink. I'm going home. I hope that I will awaken in the middle of the night, sit straight up in bed and go AH HA! That doesn't happen and as dawn arrives I still have no enlightening moment. CRAP!

The next morning the customer calls and asks what I found. I really wish I had a good answer, but as I try to explain the issue, I realize that she has no concept of what I am trying to explain. I finally just say, "I'm still working on it." She wants to know how much it's going to cost. "I don't know at this point." is my response.

"OH!" she says."

"Will it be ready for Christmas?" she asks.

"Yes!" I respond enthusiastically. I do hope I sounded convincing.

It's now time to make a decision. If I want to finish this creature in time for Christmas I will have to order a part and if it's the wrong part I will have order another part and ordering parts takes time. What to do? What to do? The control unit costs $120 and the CDI costs $60.

Time to go home. I need a drink!

I ended up calling a couple of my mechanic friends and talking with a friend here and they were as perplexed as I am. No help there.

End result, I order a CDI. Fed Ex delivers it, I plug it in, I say a prayer and spin the motor and all praise be to Micky Mouse the thing sparks like crazy. Problem solved and I need a drink.

The moral of the story: Service manuals can be wrong and sometimes experience is the best resource. A little luck helps also.

Seriously, after you have been doing this for as long as I have, I need to trust my gut feelings more. I need to have faith in what I know and not second guess my judgements. But, there are times that all you can do is go HUH?