76 KZ 900 / Fouling Plugs

I checked for air corrector jets and none there. Stock air box with brand new stock Kawasaki air filter. I did not replace the needles as they looked to be in good shape, and was not sure the Keyster needles would match . The clip is in the the 3rd slot down which is the stock setting. During the test drive , I rode it hard several times trying to assure blowing out as much carbon as possible.
Currently the mixture screws are at the stock 1 3/8 turns out. Perhaps I will open each another half turn. I'll fit with new plugs, probably go back to the hotter B7ES . Also might remove the air filter to see if that makes any difference. It seems to me the problem lies in the transition from the transition from the idle circut to the needle jet.

Without going back and rereading everything, have you actually set the pilot screws using a known good independent tachometer? Or are you just setting them at what the manual states? Almost always that is just a number to get the engine started and then you have to fine tune it. I will say this much, someone here mentioned a difference in replacement needle and seat in length. I just overhauled a set of VM26's using the Keyster kits from Japan and I had to adjust each float to accommodate the new valves. They were longer than the old ones. Not saying that is your problem but it shows there is a difference in replacement parts. Put a good tach on your bike and try to adjust your mixture screws.

Rick H.

Run with a hotter plug. At least you'll be able to ride it. Of course, you'll be setting off carbon monoxide detectors everywhere you go.
I run my bike at 11.2:1 to keep the engine cool and not really worry if I flog it. Which means I run a B5ES plug 2 steps hotter than stock. The B7ES is the stock plug.
Essentially, you want to keep the spark plug insulator nose above 450c but below 870c. Below 450c you will foul the plug. Above 870c you will pre-ignite.
Your gas mileage is going to suck and you may be diluting your oil with gas if it's super rich, but if it's not too rich you can ride it harder. A wideband o2 helps with tuning but ...money. The only thing that would concern me is that all of your carburetor circuits would have to be rich. If your W.O.T. is lean.....bad day.

Sounds like you've covered everything in the fuel arena of Fuel, spark ,compression. maybe something is happening to the spark. as the bike heats up and your loosing voltage or dwell and not getting a hot spark...

You may have to revert back to the original Mikuni internals to rule out issues with the Replacement parts.
In reality there is very little that wears in these that causes major running problems.
Apart from rubber parts ,gaskets and physical damage, the main wear parts are the float needle and seat and also fuel mix screws if over tightened and the tips missing .
The Needle jet and needle do wear slightly but it's consistent and doesn't really cause any major issues apart from a slight over richness evenly throughout .
I'm running bikes with carbs on the original 40 odd year old internals and have no problems.

zed1015 wrote: ..................
I'm running bikes with carbs on the original 40 odd year old internals and have no problems.

Same here. Ed

Good news, between mixture screw adjustments and the hotter B7ES, I finally think I'm really close. Plugs are now not fouling and have a tan color,,,,,,,,, and of course the bike is running really nicely . Finally get to enjoy the fruits of my labor on this restoration. Rode it to Cars and Coffee this morning and it got plenty of attention.
Thanks for everyone's input and suggestions appreciate the help.

I fixed your pictures. Next time click the insert all tab
Dave

That bike is way too nice to run badly! Chris

Beautiful bike!!! Ed