Missfiring cylinder, Is it my carbs??

Ok here is the story. Cylinder #4 doesn't fire, at least not all the time. After riding it the exhaust is just hot enough that you cant quite grab it but you can almost keep your hand on it. When you are driving it you can kinda hear it running on all 4 cylinders once in a while for a short burst.
This problem happens at idle and while driving.

So I have cleaned the carbs twice, the second time I pulled them off the rack and dipped them and everything.
I just replaced the carb holders and the boots between carb and airbox.
New spark plugs, gapped to spec.
New plug wires.
Wired georges coil mod.
Fully charged battery.
Ignition timing is right on spec.
Compression is in spec on all 4 cylinders
When I switch 1 and 4 plug wires the problem stays on cylinder #4.
I have bench synched the carbs and then vacuum synched them.
I have set the fuel levels with the clear tube method. I have gone slightly higher and slightly lower on the levels as well with no luck.

So switching the plug wires with no change should rule out ignition. Compression is good. So the only thing left should be carbs right?
What am I missing? I am really sure I cleaned the carbs well.

When I cleaned the carbs I blew out all the passages with compressed air after dipping them in gunk brand carb dip. I think I got them pretty clean.
How sensitive are the fuel levels? I have had them anywhere between 1/16" to maybe 3/16" below the top of the carb bowl with maybe 1/16" difference between any of them.

I also checked all the valve clearances and they where ok. but i guess the good compression probably gives that away.

What is visually observed spark quality with a brand new plug connected to #4 plug wire and held against the engine head while spinning the engine over with the ignition ON? #1 spark plug should remain screwed in. And #2/3 sparkplugs should be disconnected to prevent the engine from cranking during this test.

Is supposed to be a fat blue spark.

Also, please describe visual appearance of the old misfiring #4 spark plug. Am guessing black and sooty, but confirmation might be helpful. For example, a clean as-new appearance could indicate fuel starvation.

As known, adequate compression plus good properly timed spark plus correct fuel mixture virtually guarantees combustion. So it's a matter of zeroing in on the deficient leg of this trio.

My first guess was floatbowl fuel level being too high, but that seems to have already been addressed.

Good Luck!

According to the reported history, valve clearances have already been assured correct in this case.

However, it should perhaps be noted that acceptable cold compression psi figures do not necessarily indicate proper valve clearances. This is because too tight valves may barely seat when cold (allowing compression) and begin leaking (failing to fully seat) as the engine reaches normal operating temperature.

Good Luck!

spark is nice and blue. old plug is dark brown not quite black but pretty dark. like i said once in a while it fires on and off. I thought the float levels might be to high also but i lowered them. Currently they are just over 1/8" below the top of the bowl. I am getting very sick of pulling the carbs since I dont have anything set up to check float levels off of the bike. I can get them off and on pretty quick now though. Although my vacuum petcock isnt shutting the fuel off all the time lately so every time i take the tank off i spill gas all over now. bummer. all the gaskets in the petcock are new within the last 3 months and it used to work great. anyways that is its own problem.

i thought that maybe i didnt set the fuel levels close enough to each other but the problem is always on the same cylinder now matter how many times i change the fuel levels. and i have gone from too high to too low to what should be in spec and still have the same problem.

Would try another test run with a brand new spark plug in #4. It's not uncommon for a new spark plug to get fuel fouled beyond recovery and still look pretty good and maybe even fire a little when outside the combustion chamber.

Clear tube method is best for checking floatbowl fuel levels regardless of whether carbs are on the bike or on the bench. So long as the carbs are held steady and level during the process.

Would try to positively rule out compression and spark before further addressing carbs.

Good Luck!

well i am pretty sure i can rule out compression after 2 tests that where successful. I will try another new plug or maybe switch one from a good running cylinder. Are there any plugs that work better or resist fouling better than the regular ngk's. why do they foul out so easily. I have gone through quite a few of these in trying to get everything working right on my bike.

is there anything wrong with me running the non suppression core plug wires, no resistor caps and the non resistor ngk's.
do i have to have one resistor in there or is that only if i am worried about noise on radios and stuff.

88alltrac wrote:

is there anything wrong with me running the non suppression core plug wires, no resistor caps and the non resistor ngk's.
do i have to have one resistor in there or is that only if i am worried about noise on radios and stuff.

I run both Z1 and KZ900 the same way.

#4 plug was fuel fouled. i pulled it out and cleaned it then switched it with #1. bike ran beautifully. after i left it for a while it started to not run as well. my petcock isnt working so i think #4 carb is flooding because the float needles isnt sealing perfectly. thus fouling out the plug.
sigh. i guess i should look for a manual petcock. i just put new gaskets and stuff in the petcock not long ago and it still doesnt shut off. it is the vacuum type

how are these float needles supposed to seal. it is just metal on metal contact. not the rubber tipped needle like i am used to seeing. upon inspecting all the parts they look new. no grooves in the needle or seat but they still dont seal.