Engine will not accelerate

So I was given a 1980 KZ440 Ltd and I was cleaning it up to see if my daughter would like to learn on it! It is pretty much all there, but needed the once over to get the engine in running condition, I have worked on old air-cooled bikes in the past (first on was a Honda CB550) and many of my friends bikes growing up but this one has me stumped and I feel it is in the carbs. Currently here is what I checked, corrected, or fixed: (I have an original service manual!)
New spark plugs
Checked the coils
Set and cleaned the points
Set the timing
Checked the compression – 120 per hole
Set the cam timing – someone touched it before me and had it 1 tooth off.
Checked the valve lash
Cleaned the carbs – twice – all passages and jets are clear

So here is what it does wrong, once it is warmed up it will idle like a sewing machine, but when you try to slowly or fast rev the engine, and it starts to go above a fast idle into the midrange it misses and starves out, it looks as if the slides are not lifting fast enough. I did check the slide valve diaphragms and there are no holes and they seem to be pliable. Someone said it needs to have the air box on it to run correctly, maybe under a load but I have never seen this just sitting there running in the garage! So the other day I looked at it again and I did an experiment with the Keihin carbs that are on it, (I would rather have good set of Mikuni carbs!) trying to rule out at least something in the slide valve area of the carb. So after it was warmed up it did the same thing when you would try to rev the engine a bit, it was running without the air box, so I covered the air passages, on both carbs, on the intake side of the carb that leads to the underside of the slide valve diaphragm, then tried to rev the engine again, issue was gone!! The engine accelerated like it should!!! So what does that mean?? Are there any Keihin CV carb experts that could maybe give me an idea what might be the issue? Here is a picture of the passages I covered which make it run correctly. Any input would be greatly appreciated!!

Are you saying you are trying to run the bike with no air box or filter? If so, it ain't gonna run right. Those are CV (constant velocity) carbs, and they will not operate throughout the rpm range without appropriate air flow restriction. You will need to install the air box and filter if you have it. Ed

I do have the air box, when installed it makes very little difference if any at all! The picture in the original post are not my carb if anyone is wondering (there is not slides in them) I found that picture on the internet!

Install the airbox, air filter, and any airbox lid and then try again. The bike won't rev for crap until you fix the airflow restriction to match the jetting. Also, if the exhaust system has been modified that will cause further problems. Hopefully that wasn't the case though.

Oh, and when you "cleaned" the carbs did that include fully breaking them down, soaking all the parts in car dip, verifying the small passages such as those in the pilot jets and pilot feed passages are open? If not, your carbs are not truly clean.

I don't see any needles in the slides. Did you do the thumb test?
Steve

swest wrote: I don't see any needles in the slides.
Steve

Steve's got the eagle eye. :ohmy: Needles?

EDIT: nevermind. Just saw the response that the photo is not the carbs in question.

Did soak them overnight in carb cleaner made by GUNK, used it before and the carbs look like new! Also checked all the passages that I could with a piece of 24 gauge wire, all the jets were also cleaned with a very very small drill set that I have for cleaning torch tips that goes down to a #80! What is the thumb test?

Put your thumb over the vents after you raise them and see if they drop fast or slow. Where's the slide needles?
Steve

I've been trying to work through a similar problem on my '83. I never stopped using the stock air box, but bike runs like a new machine with the intake restricted. Otherwise, it won't rev at all until it is good and warm.
As I work through mine, if I come across a magic bullet fix, I'll let you know.

Sorry I did not get back to anyone on this issue yet, I am in the process of redoing a bathroom.... A honey-do!
I did do the thumb test and the slides drop much slower than without anything covering the port, so here is what I was going to do, I am going to re-clean the carbs with an ultrasonic cleaner we have and then try again, if it still does not correct the issue I think that the diaphragms might be no pliable enough and might need new ones. Has anyone replaced these? What is a good source for them?

Another question is does anyone know of a good solution to use with the ultrasonic cleaner? One guy I know says that simple green 50% with water will clean pretty much any carb!

Old80LTD wrote: Another question is does anyone know of a good solution to use with the ultrasonic cleaner? One guy I know says that simple green 50% with water will clean pretty much any carb!

The green Simple Green (bear with me) can be problematic on some types of metal. (Aluminum comes to mind.)

There is however a purple Simple Green you might try: it is labeled as safe for all metal surfaces. Home Depot carries it but it should be available elsewhere too.

I seriously doubt the problem is the diaphragms. Inspect them for tears and if you don't find any, put them back in and don't worry about them further.