My first bike - KZ750B4

Hello,

Some of you may have seen my thread about purchasing a new bike, a 79 kz750. Well here she is.

Was a very interesting ride home. Bike started bogging down, backfiring and lost power about 25 miles home and would not start back up even with a pop start or kick start. Lucky I was able to get it trailered home by a very awesome resident of the street the bike died on (I left a case of beer on his porch today)

After charging the battery and checking a few other things I was able to get it running again this afternoon but after a putting some seafoam in the tank and a 20 minute ride tonight the bike starting behaving the same with the bogging and backfiring.

So it seems I ma y have a battery/charging issue that I need to dig into. Battery is supposedly less than 6 months old. Before the ride the battery was at 12.4 and after the ride it was down to 11.5,

Thank you to everyone who replied to my last thread and to everyone on this forum. I am looking forward to interacting in the future. Have a great weekend.

Let it sit over night and take a reading. Might not be the battery.
Steve

Check the charging system is working per the manual. Looking at the rust on the spokes and other parts it appears the bike has seen some moisture, the wiring connection from the stator may be corroded.

Another possibility is tight valves, but I would ensure that the charging system is working first.

almost dead certain the charging system (Regulator/rectifier) is not good. How to check: get it running and rev it to about 3000 rpm with a voltmeter on the battery. It should read about 13.5 - 14.5V. If it is below that, the battery is not being properly charged.

Once you get that working, we can diagnose any other problems.

Yes,, sounds very much like a charging issue, that is actually good news as they aren't too difficult or expensive to fix. I'm going to start a new thread detailing some problems I had on my 750/4, and how i fixed it.

That bike has a lot of potential with a proper clean and polish. Tank badges and a nice paintjob would be the cherry on the cake.

Thanks for the replies everyone.

The bike definitely needs a scrubbing and rust has gotten a hold of a few nuts and bolts and of course the seat pan.
Tyrell, I would definitely appreciate hearing about some of your experiences. I like the detective work that goes into diagnoses. Ill check out your profile for threads and I definitely want to add the badges back to the tank. I will eventually go crazy with rust treatment and some rattle cans.

The battery is definitely not charging. Had the bike out Saturday night and after 20 minutes of parking lot riding the battery dropped half a volt and towards the end of the ride the bike started up with the backfiring. With the bike revving at approximately 3300 RPM the battery was only at 12.34V.

I reviewed a few of the testing procedures for the regulator/rectifier and the stator but before I dig into that I am going to have to go over the whole wiring harness. There has definitely been some hacking and crimping going on but I can't figure out why because I believe the only aftermarket part on the bike is the exhaust. Some of the ground points stink too. The reg/rec appears to be a stock piece but there was some cutting and soldering on the four(I think) wires coming out of it. It is a Shindengen Sh221-12 8.2.

I'll post up some pictures of the state of the harness now and if anyone has some good writeups/threads regarding the wiring harness or anything wiring related I would love to do some reading on it. I do have a picture of the wiring diagram.

Thanks guys,


Jordan

Sometimes a bad battery can act like a heavy load as in low resistance (shorted cells, etc).
You might just be seeing the battery sucking the life out of the regulator/dyno output.
And sometimes it can act like a light load, as in high resistance, which will let the regulator/dyno put out +14.5vdc but the battery will not absorb it.
Have you considered simply spend $65-$80 on a new battery so you can start from square one?

Here is some pictures from my phone.

You need this from kz750twins.com/?p=15




looking at pic one, those three wires taped together, If that white is going to the ignition switch - should that red/white and white have a 20A fuse between it?

If you check out my thread on GPz750R1 charging remeber yours is a two phase alternator, mine a 3 phase...just two yellows instead of three coming off the stator.

sleepinsilvia23 wrote: Here is some pictures from my phone.

OK, back up ... Not preaching here, just trying to help out. You have to do the easy stuff first.
I (maybe we) don't know when these pictures were taken in chronological order of your trouble shooting.... so if this is current, good God.

#1. Get all those connectors off, one at a time, ... one at a time so you don't get confused.
Spend some quality time cleaning them to bare metal!! And I really mean ALL of them.
Use wire brushes, fine sandpaper and some DeOxit from any electronics site or Radio Shack.

Then you can start doing the other trouble shooting stuff.

Thanks Tyrell, I have that diagram saved on my phone and the diagram from the manual. I did see that post. Gonna pull the cover off this weekend and do some testing.

Mission, do you mean the literal plug in connectors? I did that after taking those pics, there is only four around the battery. I haven't tested anything, just charged the battery and poked around at the wiring.

The shop owner who sold me the bike told me that the bike had "a shorted battery cable which was replaced".

The two ground wires that are grounded along with the battery ground appear to have been modified as do the wires coming off the coil.

What do you think of the "connectors" in these pics? Are they just old school crimp connections? Think I should start eliminating them? They look very old so they could be from the original owner.

After I feel I did some investigating into the wiring I will start testing the R/R and the stator.

Thanks again guys,

Jordan

All those insulation sleeved connectors are male and female... they get corrosion cruddy over the years and there are A LOT of them in every bike....
I can't express myself any more clearly then I did previously...clean every junction that can be taken apart.
Pull every one of those barrel connectors apart and clean them VERY well... do it one at a time so you don't get lost.
I'm telling you that half the problems DIY'rs have with old bikes and electrics is simply.... bad electrical connections from no one ever taking time to clean the joints up.
I have bought lots of bikes over the years from owners who thought they were lost causes, only to find that cleaning up the electrical connections and system (like I said), and installing a new battery.... and I'm out riding around on their discarded 'gronk" the very next weekend.
I bought two brand new motorcycles one late summer by flipping used bikes over the previous winter and spring!!