Cylinder #4 won't fire - Kawasaki KZ750 Spectre

Hey guys,

Been busy restoring my 1983 Spectre and have been driving it around for a bit. So much seems good, but I can't figure this out.

Cylinder #4 (not sure if that is right, but that's counting from left to right) won't fire. I can hold my hand on the exhaust after running the bike with no problem; the other 3 are wicked hot. I checked compression on all cylinders to make sure that wasn't the problem and fortunately it wasn't (all cylinders are around 150-155 psi). I don't know if it could be coil related, but from my limited understanding that would mean two cylinders wouldn't fire.

I don't believe it is carburetor related since I had those sent out and cleaned by a professional carb cleaner. I even took them apart myself when I got them back to double check nothing was flooding. Needles look good, floats seem to drop right, and I didn't see anything that seemed suspect, but I also don't know too much about carburetors.

I checked the spark plugs and they all seem good. I changed the wire for the spark plug/cylinder in question to the previous one I took off the bike just to test and it still didn't fire. I'll probably go out in a bit to buy all new spark plug wires, but I don't understand why I didn't get anything.

You guys have any ideas? I'm getting horrible gas mileage (around 18mpg) and the bike doesn't pull quite the same as it used to. When I began restoring the bike, I never touched the engine. I drove the bike to Maine and back before taking it apart and it seemed fine. Took a lot off, but I didn't touch anything engine related. I'm pretty new to this so I fully expect to have overlooked something simple.

Thank you for any help in advance!

Hi,
Is your bike accellerating smoothly through the gears ?

Yup! It has trouble pulling away from a dead stop sometimes (stutters a bit), but once it gets going it's pretty smooth. Doesn't pull too hard in 4th and 5th until 7-8k RPM's, which feels different to me,

Hi,
1 - 4 - left to right - correct.
This is just a thought but i reckon anything is worth a look when you have a problem.
Have you checked inside the coils connection. Years ago i had a similar sounding prob and it was not running properly on 1 cylinder (everything else spot on)
It would seem to idle and run ok but as soon as you got out on the road would surge and run very roughly.
I had installed new ignition leads on all 4 cylinders a few days earlier. Turned out a piece of the old ignition lead had broken off (maybe 5 - 10 mm) and stayed connected inside the coil connection where i couldnt see it so the spark was jumping (kind of ) from the coil - through the old ignition lead piece to the new lead . This does not work well.
Got the old bit out - new lead back in - perfect.
Have you a workshop manual for your machine.
I am no expert but check inside your coil connections and number 4 cyclinder should be 3 rd coil connection from Left to Right as i guess your firing order is same as mine - 1-2-4-3
Worth a try, ALL the best, Mick.

You know #1 is firing, so pull the #1 & #4 sparkplug wires off the sparkplugs and swap them (don't move the coil ends of the wires). Swap the spark plugs too. If the problem moves to #1 there's a coil, wire, sparkplug, or sparkplug cap problem on that wire. If the problem stays on #4 you can rule out a problem with the coil, wire, sparkplug, sparkplug cap, or anything in the ignition circuit. Ed

Have you had the carb to head rubbers off/? if you have a air leak due to no 4 not being done up tight it wont fire. Check it for tightness

Hi Eric, Check to see if the vacuum cap is missing, on #4 cyl. A Kaw shop manual is invaluable. Mine did the same, and it was a spark plug.Good luck. Bob

99% of the time that I have that problem the pilot jet is plugged up. Remove the carbs and blow thru the pilot jet hole with carb cleaner, thru the air jet on the rear of the carb and thru the idle mixture screw hole. Screw mixture screw in and count the number of turns so you know where it was to start with. Block off various ones so you know all the passages are clear. You can then either replace or clean the hole in the pilot jet. I use guitar string wire to clean mine. its cheap at a music store to get all the sixes. Others s ay it ruins them but it works for me. The hole is really small like around .009 if I recall right. Might be time for an inline filter when youre done. Hope that helps, other opinions may vary. There are several good diagrams on here about doing this