loss of power at higher rpm's

hey folks!

i have a 77 kz1000A that seems to always be giving me some kind of problem.
i just got the charging issues worked out (i think), and now it seems to want to play a new trick on me: one day on a ride it started sputtering a bit when it got up to about 7000 rpm.
it did this twice during that ride, but smoothed out. he other day it started doing it at lower rpms, and the sputtering got more severe. a bike mechanic told me it sounds like my carbs need to be rebuilt (to the tune of $400 to $600). another guy told me that there has been some bad gas going around in my area (austin, tx), and maybe i should try swapping it out with a fresh tank. i did that, used some sea foam with it, and cleaned my plugs which were carbon fouled. the bike sputtered once or twice at the start of the ride, then smoothed out and reminded me why i love that bike. after about 2 hours of riding i took a break. when i fired it back up and rode, it started crapping out again.
i pulled the plugs, and they're a bit darker than i like to see them but they dont look fouled to me.
one of my thoughts is that this may be electrical, since that end has been giving me the most trouble...
sorry for the novel, but im just trying to give as much detail as i can.

anyone?!?!?
thanks,
steve-

Steve, for all that writing, you didn't mention the state of tune of the bike... when have the valve clearances last been checked/adjusted nor did you mention whether the ignition was stock or has it been replaced. This doesn't much sound like a carburetor problem. And $400 - $600 is too much for a carb rebuild.

The only carb problem I ever had that caused intermittent bad running was when I had some crap in the tank that would go down and get into a main jet (run terrible) and then run out and run fine. The cure was to clean the tank and install inline filters. If you don't have inline filters, they are a must have.

Another problem which can cause intermittent bad running is a flaky coil. had one of those too.

oh silly me...
the ignition is an electronic mod (dyna coils, ic ignitor). ive owned it since last summer, and outside of the charging problems it has always well. ive never adjusted the valves. would they go out of adjustment quickly or would this be something that would be gradual?
the bountyhunter brings up a good point that seems to make sense to me here too.
he thinks some rust or "crap" may have found its way from the tank to the carbs, and said i should clean the tank and install an inline filter (i know, i know, what am i doing without an inline filter??). i thought about that today. also, he mentioned the coils. i think i'll test them again...
and yeah, was pretty put off by a guy "priming" me for a $400 to $600 buggering before he has even seen the bike. im pretty sure i can rebuild those carbs myself if and when the time comes.
a big part of the reason i bought an old bike was to learn about them, ya know?

thanks for the post wiredgeorge, im a BIG fan! :^)

ya know mister hunter,

the "muck in the tank " thing is something that i was thinking about today.
since it ran really well for a while before it got snippy, im thinking some crud just decided to come loose at one point.
the tank was coated before i owned it, and the coating stops before it gets all the way to the top of the tank, which i thought was a little weird. there's a little bit of surface rust that i can see, but its all at the top, and very minor. i think i may need to pull the tank and carbs and clean 'em real good.
any method you prefer for cleaning a tank without destroying the coating?
as for the coils: i'll check 'em again. last summer i bench tested them, and they showed the resistance that the manual said was good.

and no, i sheepishly admit that i dont have an inline filter installed.
i realize that for this i'm a donkey's bare behind, and will put that front and center on the list..

THANKSABUNCH,

steve-

Rust strippers are pretty nasty, I think they use phosphoric acid. Not sure what that would do to your coating. If there's only a bit near the top you might try draining the tank and scrubbing that part with a nylon brush. Anyway, even if you can't get all the rust out, flushing the tank and installing filters will help avoid the problem. On old bikes the ritual of rinsing the tank, cleaning the petcock, replacing the filters and dropping the bowls to rinse the crud out is considered routine maintenance....:laugh:

at least on mine it is.

yeah, all the methods that i know of are pretty caustic.
i think that stuff will disembowel the coating on my tank. at the same time im thinking that if it were done half ass-ed to begin with, then maybe that what it needs.
i think youre right though...perhaps ive just been neglecting some important fuel system maintenance.
i'll let you know how it goes....

thanks again,
steve-