CRAPPP!!

I was riding my KZ750B3 this week and everything on it was running fantastic. I got it to top out at 105 MPH and it was getting over 50 mpg. Then suddenly it stopped working. I am using the GM HEI Ignition module and a coil power mod and so I flipped the swith to send it back to points and it started working again so I drove off. but then one cylinder (pretty sure the right one as you sit on it) wouldn't fire from 3000 to 5500 RPM's. it would pull off the idle to 3000 and then sputter on one cylinder to 5500 then suddenly pick back up again and drive hard to the redline. I assumed it was electrics again so I started unwiring the entire HEI system so that it was back to just points and condensors. Still no luck. Now I think it might be something in the carburetor. I just put a new petcock on that has one 1/4" outlet instead of the two it used to and I never had a filter on before but do now. It worked fine with the new petcock and stuff for about 50 miles until these problems started. The engine is otherwise stock except mac 2-1 exhaust. PLEASE HELP!!

put a timing light on the wires to see if they are getting fire, I would also repalce the plugs, you may have a bad one

Might be a stupid question, but is your fuel filter plugged? 50 miles is pretty quick to plug up, but if you had any loose crap in your tank it's possible.

A bad coil can blow out an electronic ignition module, then flipping back to the standard it mught run but run lousy. Just a theory based on what my coil did to my CDI once upon a time.

It actually has a new coil on it but I will check to see if its working right when I get home. I'm pretty sure the HEI failed because I used 18 Ga wiring and I probably should have used at least 14. I guess what the question I'm asking is, are there any electrical things or possibly carb problems that would cause a problem on only one cylinder at 3000-5500 rpms??

If one cylinder is firing, the HEI must be working, unless it's firing on points-mode. Actually if one cylinder is firing, the other should be firing unless the coil or one wire is shorted to ground. (We are talking about a twin motor with single coil, right?)

14 gauge should be fine for the HEI. You are using a stock 4-ohm coil, correct, or are you using something else?

You can check for spark without turning the motor just by opening and closing the points (in HEI mode). Take out both plugs and lay them on the engine to check for spark at both plugs.

To see if the HEI is responding, just read the voltage on the C terminal. When the points are open you should get 12v, and when the points are closed you should get 0v (or maybe just slightly above 0v).

Also, just so I have more info, which version of the circuit did you build up? www.geocities.com/loudgpz/GPZheiModForPoints.html

I am using the circuit that uses the time out option and the bybass option. I built it as close to figure 4 as I could but I have no experience with electronics so this was a first try for me. You should have seen my face when I put it in and hooked it up and everything worked. I replaced the coil with what I was told was a brand new stock coil. I am going to check the ohms on it when I get home this weekend. I have been reading and rereading the stuff you have posted and I missed the part about using heavier wire in some sections. I used 18 Ga. for everything and I'm pretty sure thats what messed everything up. I'm going to use all this experience I gained to make a new HEI system for this bike and then clean the carbs again and see what happens. Also I'm putting HEI on my other bike. I still say its the best thing I've done for performance so far. I just need to use heavy wire so it will be reliable this time. One last question. How do you solder all of the resistors and stuff together?? I just have them soldered end to end or to a wire or whatever it needs. It looks terrible and I would like to do something different If I can. Thanks for all your help.

Using smaller wires won't really make the HEI go bad. They will only potentially limit the coil current slightly. If I had to guess at possible problems, I would suspect the switch first. Then possibly C1 or Q1 as they would be more sensitive to soldering heat. If you are soldering lead to lead, that could be an issue.

For something with 2 or 3 components you can get away with soldering lead to lead, but for something with more components I like to put them on a circuit board. Try to keep the leads at least 1/4" long until you get good at soldering very quickly. I usually get a generic board like this:
circuit board

You can test the HEI by itself. Hook up one side of the coil primary to the battery. Hook up B to the battery. Hook up C to the other side of the coil's primary. And make sure the heatsink is firmly grounded. Leave W un-connected. When you apply battery voltage to G, the coil current will turn on. When you remove the power from G, the coil current will turn off and you should get a spark. Test this with two loose spark plugs attached to the coil and make sure the bodies of the plugs are touching each other.

Wow thanks for all the help I really appreciate it. I will be testing the HEI tomorrow to see if it works ok. Also the switch and everything else is going to be torn apart and re made using new components and a circuit board. Hopefully that will help out. I'll post back when i figure something out.

I would try restoring the original ignition with stock coil and points and see if the problem goes away to make sure it's an ignition problem at all.

Actually thats where the problem started. The bike wouldn't start so I switched it baike to points and it started. While it was running I flipped the switch to HEI and it Immediately shut off. Now I am running it on just points and now one cylinder won't fire. I'm pretty sure its a carb problem now since I rode it for a little while without a filter on it. Thanks to everyone who replied I have it pretty narrowed down and I have some experimenting to do this weekend. Thanks everyone.

Ok, so I took the carbs apart this weekend to clean them out and I noticed that the Jet needle in one carb wasn't in its hole at all. This caused the slide to sit up a little to high and made it run so goofy. Set everything back up right and whaddya know it works right. Just thought I would post back exactly what was wrong. Thanks for all your time and help.