Adjusting the air screws

Got a nice weekend forecast ahead of me and wanted to start doing carb adjustments tonight. From what I've read, the first thing to do is bringing down the air mixture screws from the starting point of 2.5 turns. And apparently the key is to close each one slowly until you hear the idle RPMs come up slightly, right? Well so far I'm not seeing that. What I *did* see tonight was that bringing one screw down half a turn and then bumping the throttle showed a big increase in RPMs (from around 1000 to about 1800). So am I *supposed* to have to bump the throttle every time I adjust one of the screws, or should I be hearing an RPM change without touching anything else *but* the air screws? I've never had great luck with carbs so if anyone wants to spell it out step-by-step for me, I would really appreciate it.

And just to make things clear... All four carbs have been completely stripped, cleaned, and rebuilt with new jets, etc. All of the floats were set on the bench so the fuel level is approximately 3mm below the top of the bowl and then re-checked after running the bike. I also bench-synced the butterflies so they all open and close at the same time as exactly as I could feel it and eyeball it... So internally I believe everything is set where it should be. My understanding is that I should now bring the engine up to operating temp and then adjust the air screws to get the maximum RPM from each, hopefully without bottoming out any of the screws. After that, the last step is to vacuum-sync all four carbs to get the throttle exactly lined up. And that should be it?

Right now the only problem I feel is a slight hesitation every time I take off from a stop, when I first crack the throttle. I've run it up to about 6000rpm and except for taking off, the rest of the range is incredibly smooth (compared to my last bike). I would assume there's no point in worrying about that issue yet, though, until I at least finish adjusting the air screws and do the vacuum sync? I just thought I'd throw it out there in case it has any bearing on the other adjustments.

Let me know if there's anything else you need to know. And thanks in advance.

Which carbs do you have? BS34's? If so, you have pilot screws, not air screws. Opening more allows a fuel/air emulsion to enter the airflow at low speed. Try 3 turns open if 2.5 gives you a hesitation. You can go all the way to about 3.5 but beyond this the adjustment is ineffective.

Hmm I knew at one time but don't remember now exactly which carbs I have. Whatever came stock on the '81 KZ1000-K? Here's a pic if it helps?



Yesterday after closing two of the screws by 1/2 turn it actually seemed to run smoother at low RPMs. Also my wife mentioned she can really smell the gas when the bike is running, which would seem to suggest it's already running too rich, wouldn't it?

Those are Mikuni BS34s, so you will have pilot screws not air screws. Stock petcock or manual? Lift the sliders and put your thumb across the wide opening at the top of the intake throat to seal that port. Let go of the sliders. Do they stay up or drop very slowly? All four of them behave the same way when you do the test? (PS - Make sure your choke plungers are in when you do this)

@ajsfirehawk -- I think I see what you're going for there. Checking the diaphragms, right? Visually they were all in good shape, but I can't perform your test without taking the carbs back off the bike.

[Edit] I forgot to mention, the petcock is stock and I just put in a rebuild kit to get it to stop leaking.

Correct, and not just the diaphragms, but how well they are seated/sealed between the caps and carb bodies.

I checked all four plugs before going for a ride today. One had a faint bit of brown on it, but otherwise they were all black and sooty and one looked wet. Unfortunately one of the plug caps came off while checking the plugs. I pushed it back together but I think something is still wrong with it as when I went riding it felt like it was only hitting on 2-3 cylinders, it had trouble idling, and didn't have any of the power that I was feeling yesterday. I would like to get some new wires for it, but I'm completely lost here... I've been doing some reading and it appears the original equipment had resistors in the plug caps but otherwise I should use a 7mm solid copper core wire?

So I looked at Z1Enterprises, but the best I see there is a Dyna stranded-core wire . For the price I have to wonder if the quality is any good? On ebay I found a couple of possibilities with NGK. This one is supposed to fit a KZ1000 , but two of the wires have weird long plug caps on them. This set of for a KZ700 So I don't know if that means the wires are shorter or what. Both of the NGK sets seem to have a 5000-ohm resistor in the plug caps but they don't say what size the center wire is, other than they are stranded copper. I'm not cracked about what I've seen of the NGK wires that are currently on the bike as they look cheap, melt when they touch the head, and apparently don't stay together very well. Can anyone recommend another brand that will be better quality and the correct type for my engine?

I think I have some more wires kicking around here from all the parts I got when building the bike. Gonna see if I can find them and at least get things running again so I can work on those pilot screws tomorrow.

Regarding that plug cap, they're supposed to twist on, so you might have a loose connection causing misfire.
Also, I'm used to plug wires being stranded; I don't know how to put caps on solid core.
Are you missing the sleeves for your plug wires? They should have rubber sleeves to protect the wires.

OK twist-on would explain the bad connection. It was one of the inside plugs so I only had space to try to shove it straight back on. I'll be pulling the gas tank tomorrow anyway so I will try reconnecting the cap again. I also found that other set of wires (no caps on any of them), but man they look short. I'm using the stock coils and they have the screw-on connectors so swapping wires should be easy though. Oh well, I'll work with what I've got until I can find a new set of appropriate wires.

So if stranded core is normal for plug wires, then it looks like any of these sets might work. The NGKs I linked to claim to have high-temp silicon housings, so maybe they're better quality than what was on the bike. What about Dyna, anyone have experience with that brand? As for sleeves on the wires... Nada. I have two sets of wires from two different bikes and none of them had any sleeves on them.

Since you are going to have the tank off and the wires are of unknown age, you can just remove all four caps, snip off the last 1/4 - 1/2 inch of each wire, and reinstall the caps. This will give the screw in each cap some fresh, uncorroded wire to hang on to..
Truth be told, any name brand wire is going to be better than the best 20-30 year old wire. Lots of guys like NGK and Accel. You do not need any resistor in the paths, but if you do, be sure it is only in one spot. Resistor plugs, OR resistor wires, OR resistor caps.

The caps can be bad too.
Steve

After messing with the one plug wire I decided to go ahead and check all four. I *think* I may have discovered why it was running so rough yesterday...


Yeah there's no grommets or anything on the wire, that is all housing material that melted to the shape of the inside of the boot. And I can find no sign of the actual wire in there. So I replaced that with one of the other pieces of wire I have, and now it's running fairly smooth again, although after taking it out on the road I think there's still a bit of roughness to it though I'm not sure why.

Got it warmed up and adjusted the pilot screws as best I could. Basically took each one down to where the RPM dropped, backed them up until the RPM came back up, then backed out another 1/4 turn. After a quick trip up the street I decided it was still too lean so I backed them out another 1/2 turn. Took a trip around the block and checked the two outside plugs... one is completely dry and the other is half dry, and its not choking out when I take off from a stop now so I figured that was good enough to hit the highway. Overall it's feeling pretty good, has a nice acceleration and it is doing MUCH better off the line now, only needing a slight amount of throttle to take off. Also all of the backfiring has ceased and I'm no longer seeing any white smoke from the exhaust.

I think I'm close. I still need to balance the carbs and then go through the pilots one more time but it feels like all four pipes are running at similar temps now and it's idling smoothly. I'll check all four plugs later after it cools down though and see if they all match.