Strange new noise

Not sure if this is the right section but here goes. My 78 KZ 1000 has developed a new noise. Every now and then, on first start up or after sitting and cooling completely, it will have a whistle that sounds like an induction noise or big vaccum leak. The noise only lasts for 3 to 4 seconds and sounds like a vaccum chamber filling. After the initial start up I can restart the bike with out the noise returning. I've checked the induction system for leaks from the air box to the carb mountings at the head with both carb cleaner and my ultrasonic leak tester and so far have nothing to show for my efforts.

The noise seem to start after resetting the points, timing and idle speed. It was idling high and after the timing and dwell adjust the bike idles lower and runs smoother than ever. The only other thing I've noticed is that it seems a little slugglish as the motor gets up above 4,000 rpm. (If it were a car I'd be checking for a plugged converter or muffler, but, I don't think I've ever heard of this happening on a bike. Although, this bike did set for several years and even with the mufflers not sounding blown out, I guess they could be a pile of rust inside.)

Has anyone out there had a similar problem or have any additional input or ideas as to what may be causing this noise.

Thanks in advance for your assistance.

Strange, because just lately after warming up and riding it, when im setting my bike down to park, it has a high pitched noise as well for a little while, I JUST noticed it this past night.. I do know that my carb connectors have a bit of dry rot, so it COULD be a vac leak "not too expensive, btw" and yea, im sluggish "only in 1st" after about 4k.. Hm..

You say you're in NE OK? Maybe... Tulsa?

I've pretty much ruled out a vaccum leak. When I fired it up this morning the noise was still there but not near as pronounced as usual. I'm wondering if maybe I'm getting a whistle out of a carb slide until engine vaccum builds up. The sluggish part seems to be in any gear. It feels like above 4 to 5 grand that the motor gets "stuffy" and doesn't want to pull.

I live on the north sie of Grand Lake in Fairland.

Thanks

insert a ape bb 1425cc kit and that should solv your problem!

Flake of rust inside an exhaust pipe? Or maybe it is a vacuum leak:blink:, but I'm only guessing

If it is an exhaust leak it will pop on
deceleration.I had a KE100 sound like that
and run poor up top.The baffle was plugged.
Also check your crankcase and fuel cap vents.
A plugged fuel cap vent has the same symptoms.
If you have a vacume operated petcock check
for a vacume leak.

I don't know if my whistling is the same as yours but I have found my fuel tank vent whistles when pressure escapes out of the tank lid.Usually on hot sunny days. I can only hear it when the bike is not running. might not be of any help, but my bike whistles a tune now and then.