Hittin' on three ... kz1000e idle issue

I'd sure appreciate it if anyone could shed some light/experience on this. My 1980 kz1000e (shaftie) is starting to frustrate me. I have sorted several problems/issues and it's running pretty well overall, but this last one has me beat, at least temporarily. The problem is that it won't idle on #3. It actually idles fairly well on just three cylinders, but I'd really like to get it idling properly. I know it's not hitting on #3 because that exhaust doesn't get hot when I start it up and let it idle. I know that #3 fires above idle, because it just plain runs great above idle, and if I pull the #3 wire, it doesn't. I know that it's not an ignition issue because I turned the coil around and swapped #2 and #3 wires and the problem doesn't move to #2.

So the problem has to be the #3 idle circuit. I pulled the carbs today (for the umpteenth time ) and compared #3 and #4, but couldn't see anything wrong/different. I swapped idle jets, just in case, sprayed out the idle jet and air passages again for good measure, crossed my fingers and put it back together but there was no change. It seems to me that there must be a passage in the carb that I don't know about that is clogged. The passages that I found were the following:

1) the one from the idle jet to the bottom of the carb throat
2) one from the idle air screw passage that meets up with the idle jet (somewhere), and
3) one from the idle air screw to one of the small ports on the side of the throat on the output side of the carb.

Are there other passages? Is there perhaps a diagram somewhere that shows where the passages are? Does anybody have any other suggestions of what to look for? I'm getting desperate.

BTW, valves are adjusted properly and I just put a new plug in #3. I also checked the float level in #3. It was about 1-2 mm below the top of the bowl.

Check for air leak with water while idling, adj air mix screw o to 1 turn out. Cover #3 carb opening while idling does it pickup? Is there any suction on #3 while idling? check hose from carb holder and temp block it off. Do compression test on #3 cylinder.

Sorry, I forgot to mention that that compression is excellent and even across all cylinders (about 185 as I recall). I recently replaced the carb holders because of an air leak, and checked for air leaks with carb cleaner. Couldn't find any. I'll check again though. How do you use water to do that?

Use a squirter with the adjustable nozzle, also good to use on hot exhaust pipes to see hot they are.

Yes I can see how a squirt bottle would help with checking the exhaust. I've been using a wet rag.

Sorry to be dense, but I still don't understand what the water is for in checking for a leak. If there's a leak and I squirt water on it, what will happen? I know that carb cleaner will cause the rpm to increase for a bit.

Regarding the air screw, it's currently set at 1.5 out. I first suspected a problem when adjust the screw and not noticing any difference in rpm regardless of the screw setting.

Thanks for the help, BTW.

Yes I can see how a squirt bottle would help with checking the exhaust. I've been using a wet rag.

Sorry to be dense, but I still don't understand what the water is for in checking for a leak. If there's a leak and I squirt water on it, what will happen? I know that carb cleaner will cause the rpm to increase for a bit.

Regarding the air screw, it's currently set at 1.5 out. I first suspected a problem when adjust the screw and not noticing any difference in rpm regardless of the screw setting.

Thanks for the help, BTW.

rckz wrote:

...problem has to be the #3 idle circuit...air screw...currently set at 1.5 out...adjust the screw and not noticing any difference in rpm regardless of the screw setting.

Question please, to confirm -- carbs have the side located pilot air adjustment screw (and NOT bottom located pilot fuel adjustment screw)?

Also, please describe appearance of tip on #3 spark plug -- is it black and sooty as from excessively rich fuel mixture?

Thanks.

Patton wrote:

rckz wrote:

...problem has to be the #3 idle circuit...air screw...currently set at 1.5 out...adjust the screw and not noticing any difference in rpm regardless of the screw setting.

Question please, to confirm -- carbs have the side located pilot air adjustment screw (and NOT bottom located pilot fuel adjustment screw)?

Also, please describe appearance of tip on #3 spark plug -- is it black and sooty as from excessively rich fuel mixture?

Thanks.

Yes, side air screws. #3 plug will foul if left idling too long. Black and sooty. If taken out and ridden, then shut off without idling, it looks fine.

Pilot Circuit Overview

Freshly filtered air goes into a small entrance hole on the airbox side of the carb. Sometimes there's an air jet, but oftentimes not. Thinking no air jet on subject carbs with side located pilot air screw -- just the simple entrance hole. Anyhow, air enters the small entrance hole and continues along a passageway until reaching the pointed tip of the pilot air adjusting screw which regulates amount of air allowed to continue thereafter on to the pilot jet.

Meanwhile the pilot jet has picked up raw fuel from the float bowl. The air reaches the end of the air passage at the pilot jet where the air goes through the lateral holes in the pilot jet creating an air/fuel mixture which mixture then travels from the top of the pilot jet on through the pilot passage and out the pilot outlet (a tiny orifice in bottom of carb bore), from where the mixture is sucked through the intake valve into the combustion chamber.

All this is accomplished while the throttle slides are positioned completely down with no additional mixture contributed from the needle jet. And the pilot circuit continues this function of providing fuel mixture until about 1/8th to 1/4th throttle opening position. As the throttle is opened, the slides are raised, which allows increasingly more mixture from the needle jet and lessening effect of mixture from the pilot circuit.

The above is my over-simplified understanding of the pilot circuit system.

IMO, the pilot circuit is to blame for many of the sooty plug woes. And sometimes a too high float bowl fuel level causes sooty plugs regardless of an otherwise perfect carb. But in this case, the float level is reportedly okay.

Now, toward achieving a perfect (as new) carb pilot circuit --- And there are undoubtedly other and perhaps better methods, maybe even far superior methods, but here's how I do it, until learning a better way.


Pilot Air Passage

The pilot air passage throughout its entire length from entrance hole at airbox side of carb throat to the pilot jet should be clear and ultra-clean.



Pilot Passage

The pilot passage from top of pilot jet to and through the pilot outlet should be clear and ultra-clean.



Pilot Jet

The pilot jet central hole and lateral holes should be clear and ultra-clean. The pilot jet itself should be in pristine condition and the proper size. Remember, possible damage from previous cleaning efforts (with wire or otherwise) may be visually imperceptible. Holes appearing perfectly round and clean may be faulty enough to disallow the absolute precision needed to properly meter fuel intake from float bowl and infusion of air from the air passage. As new pilot jets are relatively inexpensive, I prefer to replace them. Opinions may differ, but new pilot jets worked for me. And I have yet to see any visual defect in the old original pilot jets (even with some slight magnification).


Cleaning The Passages

With carb on the bench, remove float bowl, float and pilot jet. Wear protective goggles. Plug threaded area where pilot jet was removed so as to block access into float bowl (using finger is okay). If pilot air screw has been removed, block its hole with finger. Direct carb cleaner spray into air passage entrance and blast away until spray freely exits from pilot outlet.


Pilot Air Screw

Remove pilot air screw and examine pointed tip to assure it isn't damaged. Carb cleaner spray directed into the (1) pilot air screw hole has three places where it may exit, (2) Air passage entrance, (3) into float bowl through pilot jet location, (4) pilot outlet. Any two of these may be purposefully blocked so the spray flows between the other two. Spray every combination until assured all the passages are clear and clean as new.


Let's say all the above is okay so the carb pilot circuit is perfect and performing as new. But same problem persists. Would then suspect possible problem in the enrichener circuit -- especially that the plunger might not be seating properly in its rest position after the choke lever is returned (perhaps due to crud or a defective plunger seat rubber), or maybe due to a defective starter plunger spring.

Will check to see if a diagram is nearby which could be posted.

Good Luck with the repairs!

Nothing has yet been reported about whether carbs are synched.

Perhaps carb #3 is simply out of synch, and causing excessively rich fuel mixture at idle speed.

Hoping for something simple.

They were bench synced, then manometer synced. Though I doubt the effectiveness of the latter since it really wasn't running properly. Should probably do the bench sync again.

Thanks for all the info by the way. Guess I'll be pulling the carbs yet again.