cylinder not firing

hi all -well just got my 79 kz650b3 project on the road after 7 months of renovations[10,000 miles on her]i noticed yesterday that cylinder# 3 wasnt firing and theplug was pretty black-i dont know how long i ran it only on 3 but i noticed it wasnt doing too good about aweek ago-so i went to adjust the air mix and noticed that it made no difference and the header was luke warm if that -i recently rejetted to stop it from bogging down while idling-17pilots-110 mains seemed to make all the difference untill now.could it be a simple carb problem that could be fixed by a re sync or do yopu think its a more serious problem [ring trouble maybe?]what process of elimination should i use-thanks in advance-im pretty bummed -i was just starting to enjoy my new ride ....mike:

Several things come to mind...
As Plummen always informs me KISS...

Don't adjust your carbs quite yet, first check a few things...

Plug black in carbon build up or wet as in fowled?

How old are those plugs?
Coil for cylinder 2/3 is the same so swap the spark plug wires... 3 wire over to 2 plug and vice versa... If the problem is the coil/plug wire, number 2 cylinder will be cold and 3 will be working again...

Could do a compression and leak down test...

Since 1,2 & 4 seem to be firing, assumption is proper coil voltages being developed, I'd check just the same but that's me...

Try not to be bummed, Yeah I know hard to do but take a breather, think about the situation, analyze what you do know of what is occurring or what is not operating correctly through all your measurements and then decide what to do about it... i.e. T-shooting and repair...

OMR

Swap the sparkplug wires and check again. Sparkplug caps can fail too as they contain a resistor to reduce the RFI(noise heard on radio's when sparkplugs fire).

www.z1enterprises.com sells replacement sparkplug caps. The caps screw onto the wires with right hand thread.(Left to loosen, Right to tighten).

thanks omr-plugs are only about 4 months old -looked to be a little of both[slightly wet with soot]i did notice a small crack in my #1 and 3 coil -im going to try the swap around tomorrowand see if #2 gets cold -i replaced all 4 plugs today [still no luck ]also changed the oil and filter-it had been idling alot on that oil while i was working on it over the last few months-oh yeah -if it is the coil would not both cylinders that are connected to it not fire or can one still fire on a bad coil/ thanks mike...

The ignition coils are wired so both ports/towers/where the sparkplug wires go fire at the same time. It is possible that something has failed internally so only one port gets the spark.

You might check with an multimeter set on OHMS. The primary(where the small wires connect) might read between 1.8 to 3.3. OHMS.

The secondary(where the sparkplug wire go) might read 10.4 to 15.6 K OHMS. Read between both ports.

pull the cap from that plug.......put another same type plug (new one) in the wire.....lay/kinda wedge/rest it against the top fins but rested so the electrode is pointed right at a head nut.....(dont touch it in case you got a faulty wire/cap)....thumb the starter...or even start the bike while standing next to the bike/ wire side and watch to see the purty blue sparks......easist way to confirm.....you got a partly faulty/bad coil or wire or cap i think.........good luck ...craig

If not already done, would also do clear tube test on #3 carb to assure fuel level inside float bowl is at correct position.

Even where everything else is perfect, a too high fuel level can cause the reported problem.

Good Luck!

Seriously speaking... I just LUV the responses you received from these guys where not one mention of adjust, bypass, monkey rig etc... is mentioned and that truly is the way to go regarding TROUBLESHOOT, confirm settings & analyzing the situation... Then make your corrections/replacements where required... Sweet!

Beautiful replies all... Seriously! Way cool!

OMR

if all else fails try the omr sportbike suspension mod,if nothing else it will look cool! :S :woohoo:

is pipe getting warm at all?like he said try switching plug wires from 2-3 first to see if anything changes,if not id pull drain on float bowl to see if its getting fuel.

thanks everybody-im just heading out right now to put the tank back on and try the wire switcharound-irecently checked the float levels and they were ok -i did drain carb #3 and it is getting fuel -thanks again everybody thats why i love this forum -alot of knowledge-thanks mike....

I had a very similar problem on my 750. Turned out to be a mix of several things.
Faulty plug cap, fouled plugs, and a problem in the idle circuit in the carbs.