81 KZ750H LTD No spark

Never done a points bike or car, can you add a picture so I can compare mine? I pulled the carbs apart to clean out the needle valve seats and I got the leaking to stop on one cylinder, slow way down on 2, and one had no change. I’ll also need a bowl gasket so does anyone know a good quality rebuild kit? 

wrote:

Never done a points bike or car, can you add a picture so I can compare mine?  

It's on the same page as the polarity info...about halfway down.
Make sure the point of the rotor points toward the "TEC" logo, and not away from it.
KZ Pickup Magnet Polarity and Rotor (gpzweb.s3-website-us-east-1.amazonaws.com)

Well I wasn’t finished cleaning the carbs until 3 am this morning so I had to wait to see if it would start. And sure enough, she fired right up. Hasn’t ran in 2+ years, fired right up for me!  It does need some tuning and still needs the needle valves and float bowl gasket but it runs! I actually couldn’t contain my excitement so I hopped on it and rode around my property a bit. I noticed a few things, the clutch is very very hard to pull, and my tachometer doesn’t work. I’ve got a carb synchronizer tool so that will help me a lot with the tuning. Now looking to diagnose the tach and why it doesn’t work. 

That's awesome news!

Excellent job sticking with it!  Troubleshooting this stuff is not exactly simple.

How about a photo of how you installed the new igniters so others can see how to do it on a 750?

I sure can! Question for the tachometer, it does not appear to be electrical, thus the square screw in cable would drive that correct? So could I theoretically pull that cable out and if it spins I can tell it is the gauge not working? I’ll post up pictures and dimensions when I get home tonight. 

Welp it ran, apparently only On 2 cylinders. I just figured the carbs were far out of adjustment. I pulled the plugs and noticed 2 brand new looking plugs, cylinder 2 & 3. Same coil. Darn. Well I figured I may have messed up and installed the power/trigger wires in the wrong place. I’ve added a picture, can you all tell me if green or red goes on top?

keep in mind this is the clutch lever side.  

I think the coil doesn't care about polarity.
Polarity may only affect which part of your spark plug erodes.

Welp I figured out the issue, it actually does matter for polarity and I had my wires swapped. The coils have a positive and a negative sign on the back to indicate what pin goes where and with them swapped. They do nothing, thus running on 2 cylinders. I’ll have to wait until tomorrow to test it out but I think I’ll have some change on those plugs come tomorrow morning. 

Yes, the coil polarity is marked on some factory coils, but it should not matter.  It should work either way and during various bench testing I often swap the wires and it seems to make no difference.  So it is a mystery why the coils are marked.

As F64 said, the polarity will affect which part of the plug erodes, but that is not a consideration when firing two plugs because they will have opposite polarity from each other.  So there is no advantage overall. 

In the case of a coil firing a single plug there may be a slight advantage.  You may get a tiny bit more spark when the electrons jump from the hotter center electrode of the plug rather than from the cooler ground electrode.  But, again, on a coil firing two plugs, one plug gets the advantage, and the other does not, so there is no reason to have a polarity preference.  

Maybe the polarity marks are a holdover from when they were manufacturing single-output coils, and they just kept the mold markings.

Do you have a pair of the same HEI modules?  Or are you mixing the different types?

Oh no, I swapped the coil wires and it runs a lot better now. So it wouldn’t fire with those wires swapped so polarity does matter. It runs better now. Still needs fine tuning but the swapping those wires did help it to run better

It could just be a bad crimp on one of the wires or moving something caused a connection to be re-established.  Many coils have no polarity markings and really, these dual-output coils are basically just a standard step-up transformer.  

Interesting, well it seems I don’t have speedometer or tachometer. Both seem to be cable driven and I have confirmed the tach cable has no movement during throttle so I guess that the speedometer is the same?