No spark on 2&3

[adamisalive]

Howdy all,


I have a 1981 CB750C that I got for cheap.
Been working my way through all of its troubles, and there are a lot...
One that is stumping me is that i get no spark from cylinders 2&3.
I checked the coils and they are fine as I get a spark when I swap the blue and yellow wires on the coils. The blue wire side works fine. I have continuity all the way down the yellow wire and the spark units are also working. I traced the problem back to the ignition pulse assembly.
I am going to check the timing today but I am not getting any spark at any time so it cant be the timing me thinks...  I have been reading that these pulser assemblies don't usually fail so I was wondering wether to replace it or not.

Any help would be great!

[TOOLS1]

The timing only controls when the spark happens, and does not have anything to do with making the spark. If you swapped the blue and yellow wires and the spark moved to the other coil, it would be the coil. If the spark did not move, then it could be an igniter unit. Try swapping just the igniter units. If the spark moves the igniter is bad. If it does not move, then it could be the pulse generator, or a bad connection in the wiring. The pulse generator does need an air gap between it and the rotator. You might want to check that. Also, if you do not have the Honda Factory Service Manual, you can download it for free from our manuals thread at the top of the home page.
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[adamisalive]

Thanks TOOLS,
I Checked the coils and the igniter units and all is working properly.
It is down to the pulser. I am going to check connectivity and the air gaps today.
So you have heard of the pulse ignition assembly going bad on the 79-82s?
Thoughts on whether to buy an electronic system, new or used same stock assembly or go retro and instal an old points system?
Thanks

[Re-run]

Can't say I have ever seen points on a dohc. You don't have a points cam to use, not that I know of.
If it were me, I'd buy a new electronic system, of fit on a system from another bike. Hard to say how that would work though.

[Rodgil]

The pulse generator is easy to check from the red connector, just below the starter solenoid, behind the left side cover. Use a multimeter and follow the instructions in the FSM. It only takes a few minutes to check. Mine failed intermittently, yours should be easier to check.

[TOOLS1]

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What he said. If the test shows it to be bad, or if you have ruled out everything else, replace it.
TOOLS