TOPIC:

Charles 750B wrote: Yes so when the bike ran, I moved the points to where no spark was jumping across

what does that mean? Download a manual and read it. Set the dwell and the timing. Once you know that is orrect you can set the carbs up as per the manual.


Manual available here kz750twins.com/?p=15

If you have restored a Datsun 280z including the fuel injection, then you are already above our level of expertise ! LOL. That FI was insanely complicated. I had a bunch of buddies with 240's 260's and 280's. The 280 guys had it rough when it came to troubleshooting. I loved the 260's I had as they were simple carbs, but also had electronic ignition. (I actually had a 280 motor, but with a Holley... it was the simplest, if not the best setup.)

And yes, the coil going bad can easily seem like a carb issue.

And yes, too much resistance in the secondary... suppression plug wires, resistor caps, resistor plugs can cause some spark weakness. You should only have one of those three.

When you replace the coil and it runs better, is that the only thing you change? As in, is it the only variable?
Or do you do a few other things like re-set the points, play with the petcock, etc. I guess I'm asking is it possible it could have been something other than the coil causing the issue?

All the questions aside, like the other guys, I suspect you may have a voltage issue at the coil. That is a pretty common problem on old bikes. There is quite a long path of contacts, fuses, switches and wires to provide power to the coil.

I would do a voltage check at the coil. The positive side of the coil should be within one volt of the battery voltage whenever it's running. The negative side which connects to the points will be much lower. It is the positive side that is of concern.

The biggest cause of voltage drop on Kz's is probably the fuse holders. If the wires are discolored or burnt looking, that is a problem. Sometimes just cleaning the fuse holders will make things better.

Have you had the opportunity to set the points using a stroboscope? They will reveal weak point springs and bounce with flickers and double flashes.
I'm guessing you've checked that the condensers will hold a charge, or have tried some fresh ones and that the advance moves smoothly.
Presumably you've checked for a good battery-engine connection.
Have you measured the voltage at the low tension primary connector of the coils where is comes from the kill-switch?
Should read upwards of 10v for a reasonable spark.

A high secondary coil impedance can cause internal arcing . My old kaw uses solid copper ignition wires, non-resistor plugs and NGK plug caps with ~5K ohm resistance. Approx 5K ohms total secondary resistance.

Using resistor wires and resistor plugs can cause the coils to arc internally. Electricity is "lazy" and takes / seeks the path of least resistance to ground.

In this photo from my truck coil and coil wire, I am assuming that the coil wire started to arc first., and as the coil wire resistance increased, the coil it's self started arcing to the laminated metal frame.

Thank you all for your help! Im definitely beginning to understand what is happening beneath plastic and metal casings (movement of electricity)...
So I just put in a new coil and the bike runs but the points are arcing like nobody's business...most likely condenser and over pitted points. I just bought the dyna s kit after doing much reading on it.

The fuel injection system made by Nissan was difficult, time consuming, but more straight forward than the KZ750...and it had a matchbox ignition so no points!

I hope the dyna s ignition will work nicely.

I will also see if the electronic ignition makes things better. Bike has never ran more than two days of lots of driving so it will be easy to see if Im back to square one...

Voltage is 12 to coils, 12 at breaker points, and so I think the points are just useless. I dont like fumbling around with them while pouring sweat and kicking the bike over again and again.

I do believe that eliminating the points is a good (and expensive) move but, IMHO that is not the core of the problem. If your secondary impedance is not excessive, I would assume cheap Chinese knockoff coils may attribute the bulk of your problems. Even a used OEM coil labeled "made in Japan" would be a better choice than the EMGO Chinese knockoff's. As long as it runs for a few minutes seems to be their only QC requirement. Some things break just taking them out of the package.

The points should not be arcing blue, the capacitor is meant to limit arcing . (Possible bad connections may exasperate the problems too. ) This video, if you can get past the audio problems explains the Kettering ignition pretty good. This is the type of class that I had when I was in college taking auto mechanics in the late 70's . I don't think this technology is taught anymore.

BTW< I also had classes taught by Datsun on the then emerging, bleeding edge fuel injection Used on the Datsun 280Z's. Neat stuff

Charles 750B wrote: .............. so I think the points are just useless. I dont like fumbling around with them while pouring sweat and kicking the bike over again and again.

Useless? Funny that. I've owned my 1977 KZ650-C1 since it was new (more than 42 years). It came from the factory with points ignition and it still has points ignition. I dress the points about every 5,000 miles and I replace them and the condensers about every 8,000 - 10,000 miles. It takes 1/2 hour or less to do. I have about 62,000 miles on the bike. I am not opposed to electronic ignition, my 3 cars and truck all came with it and it works fine, but points also work fine if they are installed and adjusted correctly. They do require a bit more attention than electronic ignition, but 1/2 hour or so every 5,000 miles doesn't seem excessive to one who does his own maintenance. On the plus side they do not fail hard, and I don't see how they could cause the coils to fail. My bike still has the original coils. Oh, and it starts up very easily - no need to kick it over and over. Ed

I'm on my second Dyna S. The first was shot because of a broken + terminal at the battery. Bought a new points setup and ran it until parked in 98. The points setup are very forgiving until the condencers fail. I even installed early Ford condencers in line to help the stock ones back in the day. (no kawasaki shop for 60 miles) That worked. Then the small shops started carrying aftermarket points setups but even they could have defective parts. The manual says to see if there's a spark when you short the condenser to it's body. In 40+ years I have never been able to get a spark out of them being it Honda or whatever. The only clue was the fireworks display by the points. Points can have minor sparks and the bike will still run to a point, then it won't run at all.
Tried to impress a chick in a sports car by dropping down two gears and grabbing a handful only to have the bike bog down running on two cylinders. Turned out one point set came loose so I pulled over, set it by eye and limped home.
The Dyna S is set it and forget it as long as the spark advance is working well and it is set correctly with a timing light.
I've always steered clear of cheap coils for obvious reasons. Bought a set of chrome show coils I bolted to the frame with cool looking silicon wires and boots. Miller told me they were Harley coils and I'd be better off with the stock Kawasaki ones. (more output)
In 13 I picked up a used set of late model 3 ohm Kawasaki coils to go with my new Dyna S. They worked great until I got the set of green coils I'm using now. I'm keeping the Kaw coils as spares.
Going with the Dyna S is a good move as long as the wiring is as it should be. Any bad connections or switches will put you back in the same boat but this time with a dead Dyna setup.
I suspect that's what is ruining your condensers.
Steve

I don't think the points are the problem either Ed. It's the cheap Chinese knockoff coils, and maybe a few other things, like possible Chinese knockoff points and condensers too. It's hard to find real OEM parts, and usually if you do, they are cost prohibitive.

I had a Mallory dual point on my 68 goat (was in it when I bought the car) , that one might assume would never cause a problem.. After hunting for a problem with it cutting out at 3-4K rpm, I stuck the Mallory distributor in a Sun dist machine on a wild guess. I could see it breaking up when I zinged it up. I put a OEM Delco points distributor with the little window for setting points dwell with a meter. After this, it was a caged animal.. What a difference! I had overlooked it because I thought it would no way cause a problem being "high performance" and all. go finger!

Sun Stroboscope machine. ( I had access to one at the college I went to)

As far as I know there is not a Dyna S kit for the Kz750 twin (or 400.440 twin).

You can certainly make one work by trimming it down or mounting the Dyna S pickup onto the Kz points timing plate. I believe I've seen both done successfully.

I personally have had a lot of good success with cheap knockoff Chinese coils. They were around $40 each if I recall. My buddy bought some as well. We're both using them after 5 to 7 years with no problems. As a matter of fact his bike starts faster and easier than any Kz I've ever seen. ... not that I think it has to do with the coil, and I know his motor is old and leaks oil... it;s just one of those things.

And yes, coils can break down (as others said) gradually. I built a tester for coils and this video shows clearly how a coil can start out seemingly ok. Heat and usage makes it quickly fail.

A little high tension coil theory:
A ignition coil will cut out as the revs increase, because the dwell time decreases. Dwell is the coil charge time during which the points are closed. The capacitor softens the "kick" of the points opening. (arcing)

Here is a copy / paste from googling dwell time: "Dwell angle is the amount of time (measured in degrees of distributor cam rotation) that the contact points remain closed. Initial point gap determines dwell angle. If the points are set too wide they open gradually and dwell angle (the time they remain closed) is small."

When the points open, the magnetic field collapses inducing a high voltage into the secondary winding. Two or even 4 cylinders will have a relatively long dwell time. The in line 4's have the same dwell as two cylinder bikes, because it in effect uses two Siamese ignition systems.

One thing I am wondering if the points triggered Kawasaki ignition uses a ballast resistor of some sort to reduce coil / points voltage during running conditions, that gets bypassed during start mode. (mine is electronic igniton so I can't check it)

Normally the coil is fed 6-8 volts for normal operation, yet fed full voltage during start by the starter solenoid. GM used resistor wire instead of a separate ballast resistor while most were a white ceramic square with 2 wires connected that were mounted inside the engine compartment, while some were built into the coils themselves. .



Eliminating any required resistance to the ignition could possibly account for coil and / or points failure.

Maybe cutting back on the coil voltage a bit to see if the coils will live?