TOPIC:

I asked about this last year and haven't ridden much since trying a few things. Just to bring back the story, this is on my 1977 KZ650 with the pilot screw carbs. I've had this problem for the whole time I've owned it (33,000 miles).
I believe I've tried everything. What happens is the motorcycle runs and idles great, for about 100-300 miles of riding, after this it's evident it's no longer idling correctly on all 4. If left it will eventually be unridable even on the highway whithin 1000 miles. At this time, removing the carbs and removing the pilot screws and cleaning them and blowing out the passages with air will restore good running for a few hundred miles till the same thing happens again.

Some of the things tried include:
3 different sets of bodywork, one of which was Kreme sealed.
Multiple different fuel petcocks, filters and the addition of an inline filter.
2 different air cleaner elements.
New boots carb to box, and carb to engine.
New fuel lines.
All 4 new pilot screws/orings.
Different gas suppliers.

I got 500 miles out of it this time and back to square one. I'm giving up on these carbs and going to try to get another set to function. Just wondering if anyone has ever heard of this dumb scenario. I love this bike, but I've had these carbs off now probably at least 30 times. Rediculous to say the least.

I have an idea or two.. .

What kind of fuel filter are you using? Maybe using a bronze stone kind of filter will trap more particles than a paper filter kind will.

When you say that you have replaced the fuel lines, does that mean the lines between the carburetors as well?

It sounds like you might be using the wrong kind of rubber in the lines, allowing them to flake internally from deterioration.

I see you are in Colorado. Is there a chance that your fuel is blended with alcohol? If that is the case, you will need fuel line that is designed for use with it. Normal fuel line won't work.

Thanks for the ideas. I did use the bronze stone type filter and the strange thing is when it starts idling bad, I take off the bowls and they have no dirt in them so fuel line remnants don't seem to be getting in. Another thing I didn't mention, I always take out the pilot and main jets when this happens and blow them out and make sure they are clean, then blow out the carburetor bodies. If I do "not" remove the pilot screws, when I reassemble the problem is still there, so it's necessary to remove the screws, clean them and reinstall. It's clogging right where the fuel/air mixture enters the carb at the tip of the screw apparently.

I remember this well.

Here's a link to the old thread for reference....

You are making the assumption that contamination is occuring. What type orings are you installing on the mixture screws? There is an air jet that feeds air to the pilot circuit... it is almost a straight shot depending on the type of internal passage... either almost straight or a short passageway then about a 15 degree turn to a longer passageway. Both types lead to the pilot jet well. From the pilot jet well, they come out through the pilot mix screw hole and the atomization hole. If the stuff is getting all the way through the carb, it is just as likely poor air filtration as it is crud in the gas; especially since you are using gas filters. I suggest you give some 24s a shot that are a year or so earlier than the ones on your bike... with air screws. A short/simpler air path. Talk about your air box and filter.

I'm going to do like you suggest George and try some newer carbs. I was all ready to use these carbs I've got on this 1979 KZ650 someone gave me a few years ago and low and behold they are those damn transition carbs we were discussing a couple days ago that someone had swapped on. They've been majorly fooled with too, so no luck there. I set the pilots all the way in like Kawasaki suggested and the pilots screws stick up about 3mm in each carb. This doesn't seem right. I think I found a good 1978 set though sitting here I'll clean and give a shot.
I've had enough fighting these pilot screw type. Just for info, when I replaced the pilot screws, the orings were part of the screw so they are brand new Kawasaki.

Those transition carbs are popping up all over. The needles should NOT stick up through the hole 3mm... geesh... the hole size is overbored... Kaw specs that hole size far larger than Suzuki but I bet someone has broken off needles in the past and drilled them out. They should stick out no more than 1/3mm or so at most.