no spark help

[Guest]

Ive got a 85 gs700e with bad rings and no compression so It was cheaper and easier for me to buy a 81? 750 engine off my friend and swap that in. engines look the same and from what I've read on here and other sites are pretty much the same besides the crank and pistons. Now, my question is that I would like to use the wiring harness of my 700 because my friend didn't have the 750 harness. I've hooked everything up and it turns over fine but I'm not getting spark. I really don't know how to use a multimeter but i attempted and I was getting 12volts at the orange and white wires that go to the coils. From this I'm guessing bad coils? I was looking over other peoples post claiming that they had no spark and some people said that some coils and such aren't interchangeable. My friend gave me a wiring harness off a 850 or something claiming that the guy who sold it to him said that it should work. Would those coils work?
I know I'm asking a lot here but any input would be great.

[spyug]

You won't have spark because the signal generator pickups (on the end of the crankshaft) are different than those on an 85 700 engine. There is no signal going to the ignitor. The ignitor, of course, triggers the coils. The coils will likely be fine.

While you could perhaps swap out the pick ups from your old motor, it is not an easy job as the p/us have ferrous magnets that are held in place by loctited screws. Removing the screws often destroys the magnets. An easier but unfortunately more expensive solution maybe to rebuild you engine or find another 85 mill or find an 81 ignitor and wiring.

Sorry, its not what you wanted to hear I know.

good luck

[slayer61]

By reading your post, it sounds like you are getting good (+) voltage to the coils. What you don't mention is if the (-) side of the coils are getting their part. In order for the coil to do it's job (make spark!) it needs an intermittent (-) signal. Your points or electronic ignition should be doing this job. Assuming you have electronic ignition, that feeds a signal to the ignitors. This gives you a place to start looking. Good luck, Paul

Looks like spyug beat me to it!

[MrMcTavish]

You won't have spark because the signal generator pickups (on the end of the crankshaft) are different than those on an 85 700 engine. There is no signal going to the ignitor. The ignitor, of course, triggers the coils. The coils will likely be fine.

While you could perhaps swap out the pick ups from your old motor, it is not an easy job as the p/us have ferrous magnets that are held in place by loctited screws. Removing the screws often destroys the magnets. An easier but unfortunately more expensive solution maybe to rebuild you engine or find another 85 mill or find an 81 ignitor and wiring.

Sorry, its not what you wanted to hear I know.

good luck

At least I'm finding out now though haha. would the wiring from the 850 that my friend gave me work? I was pretty skeptical when he told me

[spyug]

Again I would say its not likely unless the 850 is the same year as the engine and even then the connectors may be different. You might be able to get a better idea if you can look at fisches for the 81 engine/wiring/ignitor and for those from the year of 850.

A few years back I was checking all of these different combinations to try and find an ignitor I could put on an 83 550. I eventually found 83 to 85 700 and 750 would work but only if their pick up coils were switched over too. there are very few if any straight plug ins I'm afraid. I wrote it up in a thread called "ignitor interchange project" if you are interested.

I hope you can figure something out.

[Steve]

Besides the pickup coils, the ignitors are going to be different, too.

Not sure if the 700/750 was included with all the others, but some time during (after?) the '82 model year, the ignition advance moved from mechanical weights on the end of the crank to programming inside the ignitor. Your '81 engine will be trying to advance the timing and the ignitor will advance it even more (if you ever get it running).

You will need to source an '81 ignitor, if possible.

.

[MrMcTavish]

thanks for all the helpful advice. Ill take a look at the wiring off the 850 and the engine and see what I can do.

[MrMcTavish]

This may seem dumb but is the ignitor the same as the cdi? Is it that black boxy thing that sits near the rr and the fuses?

[Steve]

This may seem dumb but is the ignitor the same as the cdi? Is it that black boxy thing that sits near the rr and the fuses?

Well, you may be calling it a "CDI", but there is no CDI on the bike.

These bikes all use an INDUCTIVE coil discharge not a CAPACITIVE discharge.

The reason many people erroneously call it a CDI is that it's electronic. Back when the bikes were new, the "hot" thing in cars was the new, capacitive-discharge ignition system, sometimes with multiple sparks (MSD). However, our humble bikes still have a regular coil, they just have some transistors in place of points to control the current through the coils. The box of transistors is known as the "ignitor", although it doesn't actually ignite anything.

.

[koolaid_kid]

Would a Dyna S be an acceptable alternative? It would replace both the signal generator and igniter. You might be able to sell what you have to slightly offset the cost of the Dyna S.

[MrMcTavish]

Would a Dyna S be an acceptable alternative? It would replace both the signal generator and igniter. You might be able to sell what you have to slightly offset the cost of the Dyna S.

I was going to ask that as well. If I could then I would have shiny new parts that hopefully wont fail on me.

[koolaid_kid]

You would need the mechanical ignition advance unit from a different bike. The 85 700 has the advance built into the igniter, so you would need the mechanical unit that fits on the end of the crankshaft.
Can anyone else verify that the mechanical unit will fit?

[MrMcTavish]

I was taking a look at the wires coming from the crank side cover cu it was strange to me that there was only one green/yellow bullet connector comming from there. I cut the wire wrapping back and found......cut wires. Now the wires that were cut are the same color and style as the ones off my 700. Did both of the pre 82? Ish and post 82 engines have the same number of wires running from the crank side cover?