Carb rebuild question.

This not a KZ, hope you guys don't mind.....

Just got done cleaning and rebuilding the carbs on a 1973 cb350f. All went as expected with one minor exception. When I replaced the air mixture screw and the spring underneath it did not feel like there was any tension on the screw from the spring. Almost as if it was not even touching the spring. I have compared the old screw and spring to the new and they are the same. Could it be that the new spring is smoother so I just don't feel the tension from the spring pushing back against the screw?

Also, should I be able to get this bike to fire up before syncing up the carbs? I don't have a manometer. Anyone ever use the homemade kind that uses tubing and oil? If so do they work?

Not sure about your spring problem. But for sure, you sync the carbs after you get the bike running. Of course bench syncing is a good idea before you even mount the carbs on the bike.

Here's a good discussion of manometers. There are several others if you search for them.

Manometer Discussion

Good Luck

KZCSI

Perhaps there is a tiny smooth flat washer supposed to fit between the spring and screw-head which allows the screw to be turned more easily against the spring.

Or maybe, as suggested, the new spring end is simply smoother and offering less resistance when the adjustment screw is being turned against it.

If the adjustment screw also has a rubber o-ring, size and shape of the o-ring could also be a factor.

Meanwhile, would keep an eye on the screws until being sure they are not backing out due to normal vibration.

Good Luck!

Just as some clarification... you are worrying about the "feel thing" too much. Just put the screw in and turn it out 1.5 turns or so.

Patton, in 73, I can't recall any carb vendors using pilot fuel mixture screws, only air screws. Air screws quite often use orings fit onto the body of the screw. The little washer doo-dads you seem to be bringing into this are used on later pilot fuel mixture type screws where the tips were very sharp. Those things are assembled with the springs going over the screw, then you put on the metal washer and last the rubber oring which provides seal. Any of our CV series carb owners will vouch for this.

Mr. TheTrout: If you ever decide you have the overwhelming urge to disassemble those carburetors, you will probably end up ruining them. When you take the throttle shaft out, you have to KNOW there are two keys that sit down in channels that MUST be removed in order to remove the shaft. It isn't intuitively obvious. They are HARD to remove. I speak from experience. The keys were the 1973 contribution by Keihin to the advancement of stupid since the keys serve NO purpose that I can see. I would wax poetic on poor engineering by Keihin... just finished a set of VN750 carbs.... geeeesh, did they REALLY have to make them that complicated as well as prone to messing up? Oh well.

Carbs came apart fairly easily. I followed the cylmers manual. I did just what you said on the air mixture screw. It just seems like the new screws have no tension like the old ones. I should have those carbs back on the bike this weekend. I'm kind of curious how I did on the rebuild, we shall see when the time comes to hit the starter button.

If you totally disassembled those buggers, you have my admiration. It takes me two full days of work to finish a set of those things. Good job! Let us know how they run!

No, that was not a total disassemble. I spent about 2 hours per carb. I have no parts cleaner so everything was done by hand. I replaced the following and cleaned everything in between:

needle jet and clip
float valve and seat
pilot and main jet
air mixture screw and spring

I just got done putting everything back on the bike. Got one bolt on the airbox I can't get in. No back blinkers due to taking of the 1970's backrest. Still have to replace the 1970's mini ape hangers with the drag bars I bought for it. I should be firing it up this weekend. Wife stopped out in the garage before going to bed and asked if she gets to ride it too!

wiredgeorge - either way about it you will hear about it.

OK, got everything put back together and fired it up. It starts with just half a kick. Starter is not working, but that is most likely the battery. The bike idles fine at 1200 rpm. Now for the problem, I have one cylinder not firing. I was kind of surprised because it starts so easy and idles just fine. The plug was wet when I pulled it. I checked spark and the thing started up so I got a real good look at the spark on that cylinder and it was good too.

So I suppose the first thing I will do is get a new battery and see if that changes anything. If not then i can only imagine it is that one carb. I think pods are in the future of this bike. The damn airbox is the worst I have ever had to remove!

Gotta get this one done. Race season starts up soon and the ole KZ needs some maintenance too!

Wish me luck!

TheTrout wrote:

... one cylinder not firing...plug was wet when I pulled it. I checked spark and the thing started up so I got a real good look at the spark on that cylinder and it was good too...first thing I will do is get a new battery and see if that changes anything. If not then i can only imagine it is that one carb.... quote]

Would also put a brand new spark plug in the missing cylinder, regardless of how good the existing plug looks and regardless of whether it test fires when not screwed into the head.

Relatively new plugs can look just fine and seem to fire okay when tested by holding against the cylider head, but then continue failing when placed back into service.

If applicable to these carbs and not already done, would consider checking the service fuel level inside the float bowl of the carb feeding the missing cylinder. A too high fuel level can cause excessively rich misture and fuel-foul the plug. In my experience on the Z1 and KZ900, the NGK plugs, once fuel-fouled, never seem to recuperate.

Good Luck!

Actually Patton, I have had just that happen before on an old 3 wheeler. Took it into the shop because I couldn't figure it out and all they had to do was put a new plug in. I really suspect the carb. I am going to get a new battery today since it needs it anyway. I'll swap plugs with another cylinder that works to see if it is the plug. I am going to go this route because after sleeping on it I really think I need to pull the carbs. I think I knew that all along but came here to ask in case there was a simple test AND because I did not want to pull those carbs off again. The air box is a very tight aqueeze!

So I finally found the time to pull my carbs off that I rebuilt. Bike was running on 3 out of 4 cylinders. I checked the carb on the non running cylinder to find a float in upside down! Bike runs pretty smooth now. I need to adjust and sync them and that part should be done. New battery, new tires and put on the new handle bars and it should be ready for the road! I can't believe how smooth a 35 year old bike can run!