Spark Plug Gap

Luis ,
Your voltage numbers look off, but you're getting spark so we'lll move on.
Gavroyer is right. You should check how good your ground connection is on right cylinder.

ignition on/ engine off
meter dc v
Black probe on the right cylinder's spark plug's hex nut while the plug is installed in the head
Red probe on the positive battery post.
note voltage

move black probe to the negative battery post
note voltage

do both plugs fire outside of the cylinder if they were laying on the cylinder head?
Be careful of this , if there is gas in the cylinder when you do this you will possibly have a fire when you crank the engine.
get a fire extinguisher just in case

"It only takes a moment’s inattention to start a fire. I’ve seen smart racers flood an engine, pull the spark plugs, and then hit the starter button. But if someone forgot to turn off the ignition switch, a spark from the ignition wires can turn the gasoline being pumped out of the cylinders into a flamethrower. It’s not a pretty sight." David Reher of Reher Morrison Racing Engines
rehermorrison.com/tech-talk-68-playing-with-fire/


How is your fuel mixture in that right cylinder? If it's really lean, the plug may have a tough time firing

Excuse my delayed response. I've had construction going and haven’t had a chance to mess with my bike. I finally got around to measuring the voltages.

meter dc v
Black probe on the right cylinder's spark plug's hex nut while the plug is installed in the head
Red probe on the positive battery post.
note voltage: 12.8V

move black probe to the negative battery post
note voltage: 0V

Both spark plugs give me the exact readings. Both spark plugs do spark when outside the cylinder head.

were you able to gap the spark plugs at the factory settings?

They spark perfectly at factory settings outside the cylinder head but no spark inside.

Sorry if this was already covered, but if the advancer was taken apart and put back together at some point and the bike would not run after that, it is possible the cam lobe is 180 degrees in the wrong direction. This will allow the plugs to still spark, but the bike won't run. It might have the appearance that there is no spark inside the engine.

I'm not sure what the advancer looks like on the 750 twin, but there is usually something indicating which way to set the cam lobe rotor. On this 4 cyl model, there is a tic mark on the edge of the rotor that should line up with the "TEC" logo, or possible the hole near the logo.

Luis,
Have you put the carburetors back on and tried to see if the engine actually starts?

Thank you. It’s not been covered. I had that issue back in January and was not the easiest thing to figure out. The problem I'm having now is the spark plugs fire outside perfectly right when the F shows up in the timing advancer but won’t spark once installed if set to the gap recommended by the manual (.7mm). If set to something like .35mm or less it will fire, but of course the bike is not running as it should.

I haven’t, I'm going through all the wiring at the moment to see if I find a cable that's causing this whole issue. My guess is there's a cable somewhere making just enough contact for the bike to run but of course not running as it should. In my mind it makes very little sense that the bike starts up one day (using the .35mm gap) and the next day it doesn't.

One thing that caught my attention is I measured the batteries voltage this morning and it was .5 volts lower and it’s been connected but bike's ignition/electrical system off. Could there be a current leak that's slowly draining the battery when the bike is off and more so when the bike is on? It could make sense, since the spark plugs are not getting enough current to properly spark inside the cylinder head.

When was your bike running with .35 spark plug gap and what did you change after that?
What coil did you buy?

Hello, It’s been a while.
I got my bike to run!!! I installed new B6ES plugs at the specified .7 mm gap and she starts beautifully.
Only issue I’m having now is she won't idle nicely below 1,500 RPM. :S

I'm running Mikuni VM-34s with stock pilots 20. I've tried every pilot from 10 to 45 and the bike always seems to run too rich, it fouls the plugs quite quickly. And I always end up having to set the mixture screw out almost 4.5 turns. INSANE! Does anyone have luck running their KZ750B with the VM34? Seems impossible to get her to idle.
Thank you.

I'm having similar issues with the VM34 carbs on my KZ750 Twin. I'm running super rich and fouling plugs, even with B6ES plugs. 

I just got a set of 10 size pilot jets, hopefully that helps. 

The bike came with the VM34 carbs when I got it, but I kind of wish I had stock ones now. 

Its very common with these old carbs for the 'choke' plunger sealing rubbers, (at the end of the plunger), to go hard and not seal correctly, causes a lot of issues, I believe you can still get the assembly new but all is needed is the rubber on the end. In the u.k. a guy offers this refurbishment service although it can't be too difficult to dig them out, make up and refit new. Due to the amount of ethanol in the fuel viton would probably be a good choice.