Pulse Generator Transplant

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After troubleshooting every other electrical component on my 1984 Honda Shadow VT700C, I determined I’m not getting spark because I have a bad pulse generator. Later model bikes use a single pulse, but the ’84 VT700C has two pulse generators, one for each cylinder. This equates to double the possibility of failure and headache cubed when one or the other it actually does fail, since they have to be replaced together as an assembly.

Testing the pulse generators is a pretty simple process of disconnecting the pulse generator assembly from the rest of the electrical system and taking an OHM reading on the leads for each pulse generator. The connector is easily assessable, tucked away on the right side of the crankcase by the fuel filter.

One of the pulse generators tested at 440 OHMs, well within tolerances. The other pegged out my multimeter, indicating a bad pulse generator.

Finding a “new” OEM replacement proved to be impossible. At least three websites claimed to have the part, but when I spoke to a live salesperson, in each case I was told the part was discontinued and no one manufactures a replacement.

I tracked down a used pulse generator assembly on eBay. It’s amazing that idiots like me desperate enough to spend $100 for a $10 part. Since the one I picked up was the lowest priced on eBay, and since the VT700 is scrap metal without one, I considered myself lucky.

While testing the pulse generators is easy, replacing them is a pain. I had to remove the right foot controls, the right-side exhaust, part of the frame, the right crank case cover, and both the clutch inner and outer.

Before installing the “new” pulse generator assembly and putting the bike back together, I decided to test it. Just like the original, it had one good pulse generator and one failed pulse generator.

In the spirit of Dr. Frankenstein, I began hacking at the two assemblies, tossing the bad generators in the junk bin and cobbling the two good generators into a single pulse generator assembly.

When I began routing the pulse generator wiring back through the crankcase, I discovered I had shorted one cable by half an inch. Clearances are tight in the crank case, with the wiring routed around several moving parts, so that half inch may as well have been a mile.

I set my Frankenstein’s monster of a pulse generator assembly to the side, and decided to take a break to check my email and check the status of some other parts on order from eBay. On a whim, I checked to see if anyone had posted another pulse generator assembly.

And there it was: a pulse generator off of a 1983 Honda Shadow VT750, for $15, plus $5 shipping. What did I have to lose?

This assembly arrived two days later. Both pulse generators tested within specifications, and it routed perfectly into the crankcase.

Now it’s time to button this thing up and see if we have spark.

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