TOPIC:

Hi
A few months ago I finally got my KZ750B4 back on the road after a lengthy restoration. Ran pretty well, went for a short ride about 10kms (although I thought might need some fine tuning) plugs were carboned up.
Few days later went to start bu t then it misfired,coughed and blew back through the carb.
So I tore down carbs, cleaned, checked needle height, rechecked fuel,float levels.
I did a test on the slides, as I read somewhere that the slides should fall slowly with vacuum. About 10 seconds.
I have near new diaphragms, however they fall quicker within 2-3 seconds.
I also have what I think is a weak spark. Thin white/blue spark.
Have checked battery fully charged 12.8 v.
Coil resistance test within range,
voltage to coil good ,
voltage from coil to points good.
Charging when running test 13.5 v
Have checked ignition timing twice
Checked valve timing twice.

It’s got my baffled. Not sure if it’s ignition or fuel problem.
Plugs are black with carbon. Some slight wet around top edge of plug.
Could this be too much fuel?
I did think it used a lot of gas on my first ride

Can anyone help please, I just want to ride !

Pics of the plugs?
Steve

Cleaned plugs , added fresh fuel and tried again today
Only rough idling , then misfired when open up throttle approx 1/4 throttle , will miss if I twist throttle fast.

Looks to be running way rich, on idle at least. When you striped the carbs did you colourtune them before your first ride and when you can get it running for long enough now balance them on the bike. Didi you bench sync them first?
Could also be gummed rings and burning oil, any smoke when you took it out? A compression test would answer.

What model NGK spark plugs are you using? Ed

If not already done, would assure valve clearances are within specs, and also perform clear tube test on carbs to assure fuel level is within specs (not too high).

Good Fortune!