Cylinder 1 no fire. Appears carb related

After waiting a couple weeks, I received my Dyna S replacement for my burnt out Dyna III, so I finally have spark and the bike runs!

But Cylinder 1 is not firing, as confirmed by the water test on the pipes, and pulling off the plug wire while running has no affect. Problem exists both on and off idle.


*** What I've tested ***
There is definitely spark. Tried swapping plugs, new plugs, swapping wires, and it always has spark with the plug removed. Pulled plug is usually mildly wet.

Did a compression test just on cyls 1 and 4. Both were 120 psi. I haven't done any valve adjustment since I got the bike, but as long as there is compression, that shouldn't matter at this point.

There is fuel in the carb bowl (drained both 1 and 4, both had similar amounts of fuel. I haven't done anything with the carbs aside from pulling them off the bike when I first got it and looking in the bowls.


*** What I've narrowed it down to ***
If I put my hand over the #1 carb throat, it suctions onto my hand just like the other cylinders. When I release my hand after holding it there for a couple seconds, the cylinder seems to fire momentarily (the idle goes up for a couple seconds and the exhaust pipe finally starts to get warm). I think this is the answer to the problem, but I am new to carbs & not sure where I should start. I've been searching these forums, but haven't been able to find exactly what I'm looking for.

[url=http://kzrider.com/component/option,com_joomlaboard/Itemid,33/func,view/id,143053/catid,3/
]More info on my carbs[/url]

Thanks!

Would first check pilot adjustment screw to assure it being approximately same as other carbs. It might be set too rich on #1 carb.

Would next first check service fuel level in float bowl of #1 carb. It's a quick easy check with no disassembly required. Use the clear plastic tube method. Check all four carbs while you're at it. If level is too high, can cause excessively rich condition.

Would also check valve clearance. Cold compression may be okay but tight valve begin to leak as engine warms.

It does sound like a carb issue. I think you have done enough to rule out electrical at this point. First thing to do is to check the fuel level in the bowl. Use the "service fuel level" method. I am going to assume you are using Mikuni VM26 carbs that came stock with the bike? You can check the ID mark on the flange to see which carb assembly is being used... but in any case, the line of gas should be about 1/8" below the gasket mating line. With a bike on centerstand, you can put a hose into the drain opening making use of a a 1/4" vacuum fitting with some teflon tape to stop leaking. You can screw the 1/4" plastic vacuum fitting in and then hook a clear hose to it. Hold the hose next to the carb body and tap out any air bubbles. DON'T MOVE THE HOSE once in place as it throws the measurement off. If the gas is where it should be, fine... if not, then you will have to remove the bowl and bend the tang on the float to adjust. More gas needed? Bend the tang down a tad and recheck. Less gas would be a bend up. Anyway, once you are sure there is the appropriate amount of gas and if the cylinder doesn't fire, REPLACE the pilot jet. Should be a #17.5 pilot on a KZ900. You may want to not trying cleaning the pilots as this is generally a waste of time. See if this doesn't cause the cylinder to kick in right off the get-go.

Thanks, guys, I'll check into these things tonight.

wiredgeorge wrote:

I am going to assume you are using Mikuni VM26 carbs that came stock with the bike?

I had a thread up about identifying the carbs a couple weeks ago - Carb Info
You said, "I believe those are pumper carbs VM26SS from a 79 LTD that have been line bored."

I had forgotten that thread... if I owned 26 pumper carbs, I would replace them with non-pump carbs. The 26 pump carbs are VERY hard to tune and I have had poor luck with them over the years. They weren't used on many models and the tuning info is contradictory and I haven't had much luck figuring them out as far as tuning goes. They don't show up in the KZ1000 factory service manual and Clymers gives some strange advice.

Does the cylinder start to fire over 1/4 throttle? I just found out myself that pilots work at idle to 1/4 throttle. Does it fire with the chock on?

If you drained the bowls and have the same amount coming out I wouldnt mess with the float hight till you clean out the pilot passage or replace the pilots.

wiredgeorge wrote:

I would replace them with non-pump carbs. The 26 pump carbs are VERY hard to tune and I have had poor luck with them over the years.

Not the news I wanted to hear

I just remembered, when I had the bowls off before, each one was missing at least one part or more from the check valve setup. Could this possibly cause too much fuel to be drawn in to that carb?

If I were to replace the carbs, is there a certain year that is preferred over the rest? Sounds like the 26's are better for drivability, but the 28's for performance? Is the VM34 or VM36 conversion really worth it?

Snakebyte wrote:

Does the cylinder start to fire over 1/4 throttle? I just found out myself that pilots work at idle to 1/4 throttle. Does it fire with the chock on?

Cracking open the throttle doesn't seem to make it fire. Will further test that tonight though. Choke doesn't make a difference.

A missing check valve will cause that carb to overflow very quickly.

I assume I could just cap off the accel pump inlet to that carb (at least temporarily) or pinch the hose to rule this out as an issue?

Wanted to be 1000% sure it was a carb issue before I started messing with the carb... So I shifted the carb assembly over 2 cylinders so a known good carb was on the non firing cylinder :lol:

And it fired!

So after supper I'll be running some more checks on that carb.

Got her hitting on all 4 earlier tonight!

The pilot jet was clogged up, so I made an attempt at cleaning it with a strand of copper wire & carb cleaner. Got it so I could see light through it, threw them back on the bike & still nothing. Pulled it back apart, swapped the pilots between 1 and 4. 4 still fired, but 1 still wasn't firing. Pulled them off again & sprayed a ton of carb cleaner through the jet with it still installed in the carb. That seemed to do the trick!

Thanks for the help