HELP!!! It won't run on #4!!! I'm at my witts end...

Okay, here's the story:
1980 KZ550C. I have been working on it and trying to get it going. So far I have gotten it to run run well on Cylnders #1-3, but it just won't run on #4.

Here's what I know:
The carbs have been cleaned and rebuilt and bench synced. (A few times now)
The valve adjustments are spot on for intake and a little tight on the exhaust. (The PO had the exhaust clearance on # 4 set at 0, it is now at .040 - clymers AND the local Kawi dealer say spec is between .060 and .10)
There is suficient spark.
The spark plugs are new.
the timing is spot on.
The exhaust pipe is clear (I was running out of things to check).
There is plenty of fuel flow to the carb, the float height is a little high, but within an exceptable range.
Compression is good on all four cylders as well.

When I squirt gas straight into the back of the carb on 4, the bike picks up and runs better but quickly dies back down again. I have a steep driveway, and when I am taking it out of the garage, when I get about half way down the driveway, #4 kicks in and runs strong for a couple of seconds and dies again. When trying to take it down the road, at about half to full throttle, it tends to kick in and run choppy, but on all four, anything less and it dies.

I have tried everything that I can think of to get this bike to run and have come up empty. The only other thing I can think of to mention is that with the air filters off, I can hold my hand over the back of the carb (Choking it out) and with the gas build up it does start to run on #4. BUT, I feel very little suction as compared to the other three carbs. Would this be a clue that might lead me in the right direction on this?
I know it has to be a fuel issue, and the local shop agrees, but I have checkd everything that I cam think of and it still isn't right.

Please help!! I am at my whitt's end on this one. Thanks, all!!

You mention bench synch, have you used a mercury carb synch on them? What kind of shape are the carb holders in? I mean the rubber bits than hold the carbs to the head? If theses are cracked and/or leaking then performance can suffer.

hope this helps...Sam

With respect to valve clearance, if memory serves these bikes are happier with the valves a little loose rather than tight (but I stand to be corrected) It shouldn't affect performace all that much.

KB02 wrote:

Okay, here's the story:
1980 KZ550C. I have been working on it and trying to get it going. So far I have gotten it to run run well on Cylnders #1-3, but it just won't run on #4.

Here's what I know:
The carbs have been cleaned and rebuilt and bench synced. (A few times now)
The valve adjustments are spot on for intake and a little tight on the exhaust. (The PO had the exhaust clearance on # 4 set at 0, it is now at .040 - clymers AND the local Kawi dealer say spec is between .060 and .10)
There is suficient spark.
The spark plugs are new.
the timing is spot on.
The exhaust pipe is clear (I was running out of things to check).
There is plenty of fuel flow to the carb, the float height is a little high, but within an exceptable range.
Compression is good on all four cylders as well.

When I squirt gas straight into the back of the carb on 4, the bike picks up and runs better but quickly dies back down again. I have a steep driveway, and when I am taking it out of the garage, when I get about half way down the driveway, #4 kicks in and runs strong for a couple of seconds and dies again. When trying to take it down the road, at about half to full throttle, it tends to kick in and run choppy, but on all four, anything less and it dies.

I have tried everything that I can think of to get this bike to run and have come up empty. The only other thing I can think of to mention is that with the air filters off, I can hold my hand over the back of the carb (Choking it out) and with the gas build up it does start to run on #4. BUT, I feel very little suction as compared to the other three carbs. Would this be a clue that might lead me in the right direction on this?
I know it has to be a fuel issue, and the local shop agrees, but I have checkd everything that I cam think of and it still isn't right.

Please help!! I am at my whitt's end on this one. Thanks, all!!

KB02 wrote:

..................... the gas build up it does start to run on #4. BUT, I feel very little suction as compared to the other three carbs. Would this be a clue that might lead me in the right direction on this?...........

Missing vacuum cap on the appropriate carb nipple or intake manifold ???? Probably a stupid suggestion on my part as I'm not even sure if yor carbs are set up for vacuum caps.

if your carbs have vaccuum slides check for pinholes in the diaphragm

the Carb holders (boots, whatever) are good and in great shape. I have not used a mercury syncer on the carbs (I do own one) because I cannot find anywhere to hook one up and my clymer's manual is less that usefull in the matter.

As for vacume lines, the diamphram for the petcock is shot and a new one is on order, but even with that vacume line completely closed off and using the prime position on the petcock it still has the same effect. with the line completely off the engine, it does run worse. I have NOT yet tried the vacume line that leads from the "carn holder" boot. I'll give that a try tomorrow. after I get out of work.

Any other suggestions? I'll take everything that you guys can throw at me...

Thanks!!!

I dont know much bout carbs, so correct me if im wrong. I had a similar problem with my bike and the problem was in-between the intake boot and the head. There wasnt a tight seal cause the boot had a small nick around the edge which in-turn caused a intake leak. Every time I lifted the carbs a lil it would kick in and run great. If you know your gettin a tight seal between the carb and boot....then check the other side. This I do know.... Poor mans way to see if you have an intake leak , get a can of B-12 (carb cleaner) and give it a quick blast around your intake boots...(while engine is runnin) if you hear the idle change, then you have an intake leak. Delt with that prob right before my wiring harness fried!!! Good luck.