TOPIC:

1980 KZ550c.

If any of you had been reading my other post about getting this bike back on the road on the carbs board, you know the basic history, but rather than kee that post going, I thought I would start a new one just on this particular issue.

I can't seem to get the bike to run consistantly on cylder #1. I origanlly had issues with #'s 1 and 4 and thought they were related, but as it turs out theye were different issues. Here are the basics:

The carb is clean. All air, idle, and main lines are as clean as they can be. Stock jetting with the needle currently set at 1.5 turns out. For most of my testing and fixing, the air filters has been off, but even with them on, the problem remains. If I hold my hand over the back of the carb, the jug will catch and run for a second, then die off. Adjusting the needle all the way in or all the way out makes no difference.

The engine: I have good compression according to my manual, but it is about 15 psi lower that the other three cylnders. Timing is set spot on acording to a timing light. Valves are set to within spec (although exhuast is a little tight, but not tight enough to make me worry just yet).

I have great spark. In a dimmly light garage, I can hold the plug on one of the head bolts and see a briliant blue flash jumping around on the electrode.

For some reason, I just can't seem to get the fuel into the cylnder to meet the spark. Any suggestions?

Post edited by: KB02, at: 2006/10/29 09:00

have you checked the emulsion tube for that carb? its the brass tube that the needle slides into. you can pull it out and check it. see if all the holes are clear. good luck. maybe check the vent too. it may be clogged. not letting enough fuel in?

Post edited by: arobsum, at: 2006/10/29 09:21

Here's a shot in the dark while accepting that everything is perfect with the carbs, ignition, and compression --- Possible intake leak through the #1 intake manifold resulting from being loose, cracked or otherwise damaged or poorly connected (is the clamp tight) or maybe the rubber vacuum plug cap is defective, or other condition allowing intrusion of outside air into the carb manifold. Could be very wrong about the diagnostic method, but seem to recall reading somewhere about spraying starting fluid onto the intake manifold with motor idling and if caused the cylinder to pick up (akin to blocking air from the intake side as you previously mentioned) could indicate unwanted intrusion of outside air. Just a thought and may be way off base, and sorry if I missed seeing coverage of this aspect in the earlier thread.

Post edited by: Patton, at: 2006/10/29 10:22

Post edited by: Patton, at: 2006/10/29 16:08

is it dead all of the time, ie. at idle bring it up a few thou, rpm, and then a few more, see if the pipe gets warm then

Try blowing on the vent hose w/ the petcock on prime. I found that on my 550 I'd get some air bubbles in the system, which didn't let the gas get all the way to the carb/cylinder.

Be careful though, cause it creates back pressure which will bring the gas up and dump into the airbox/out the tube if you're not careful

It eventually just cleared up - haven't had to worry about it for the past couple days, after having the bike on the road for a week or so.

This is definitely a 'kick it and see if it runs' solution.

The Intake boot is fine as far as I can tell. I will try the spraying trick on to see if that helps or not. And I will also check that vacume cap. Again, to my knowledge, it's fine, but it's worth double checking.

del

That cylinder is running lean because when the air box was removed the signal through the carb weakened. Because of the 15psi drop in compression in that cylinder, the signal does not become strong enough to pull gas through the carb until you speed up the air flow through it by increasing rpm. Check all the slide heights that they are equal. Jetting all four carbs idle curcuits richer may improve performance dramaticly. If the carbs have rubber plugs inside the bowls make sure they are sealed. Float level must be on. Bouncing on the bike will cause sloshing fuel to boost its way up to the venturi and the rest is history. Rings get washed out by fuel leaking when the bike is on the side stand. Compression loss over time is the result. Anytime an air box is removed fuel to air ratio is altered. Just needs more gas, no big deal. If you could saw the hand off a manniquin at jc penney's without anyone seeing you, and wire it over the carb you'd get your idle back.

nads.com wrote:

That cylinder is running lean because when the air box was removed the signal through the carb weakened. Because of the 15psi drop in compression in that cylinder, the signal does not become strong enough to pull gas through the carb until you speed up the air flow through it by increasing rpm.

I am using pods for filters, just so you know, and while I agree that having the filters removed will alter the air flow cuircut, why should the other three cylinders run fine without the filters? And even with the filters put back on, I am having the same trouble. Unless I running WOT, #1 won't kick on at all.

With a brand new plug in #1 clyinder, does it fire okay for even a short time and then foul out? This could possibly be from the float level being too high resulting in a way rich condition. Anyway, that's what happened to me and correcting the float level to a leaner position (lower) cured the problem which hasn't recurred since. I realize you believe the float is okay and I don't mean to beat a dead horse (please forgive me), but it is just so very similar to the problem which plagued me with #1 doing great with a new plug for a few miles before fouling out and running on three cylinders again. Bought many new plugs before figuring it out. If excessive richness is causing the misfiring #1, I realize there are several other causes for this condidion, it just happened that the improper float level was the culprit in my particular case.

After re-reading your post, it seems excessive leanness instead of richness is the problem. Could also be caused by improper float level (meaning too low and therefore starving for fuel due to premature closing of the float needle passage.)

Post edited by: Patton, at: 2006/10/31 10:02

Well here is what I have found:
I tried the spray trick on the intake boot and found that I did, indeed, have an air leak on #1. I pulled the carbs and all the intake boots, sealed all the surfaces with High Temp silicone sealant and have reinstalled. I am going to wait untill tomorrow to test to give the sealant time to cure.

I did also check the float high, and it is where it should be. So that shoud be all set.

I have tomorrow off, so wil have time to play a bit more once the sealant is dried.

Hopefully, that was the issue and a quick (so-to-speak) carb sync will put it back to running like it should. I'll let you all know how it turns out. If you just see allot of #@$%$%%*^#$%#$%'s and Grrrrrrr's, you'll know that wasn't the problem.

Its gonna run!! Thats alot of writing for an air leak. That's why I wrote so much. I knew you just needed a jump start. VRRRROOOOOOMMMMM!