Hesitation around 5000 rpm

[Toonces]

I've done some searching and found out how to solve the notorious off idle "Stumble" but my bike has never done that. The problem I have is a pronounced hesitation between 4500 and 5500 rpm. It seems to be the worst at about 5100 rpm. The hesitation is random but consistent in that there is no set pattern as to when it hesitates but will do it about once every minute and a half or so on average. It can hesitate twice in 30 seconds or not hesitate for two minutes. It only happens when holding a steady speed. No matter how fast or slow I accelerate or decelerate through that rpm range, it will not hesitate. Only at a constant rpm. I did partially engage the choke (starter enrichening circuit) and it did noticeably lessen the hesitation. That makes me think it might be lean at that throttle setting which is about ¼ throttle. Other then being typical 80's cold blooded starting and slow to warm up, the bike runs good.
The bike has 7,700 miles on it and was in storage for a very long time. The tank is not rusty and I removed the carbs and cleaned them before I rode it as the accelerator pump nozzles were clogged and not aimed properly. Unfortunately I did not record what the jetting was so don't know if PO did any rejetting. I also check the YICS box and hoses and they seemed to be good. I plan on removing the carbs again but wanted to get some feed back from this forum before I started the project.

[YellowJacket!]

If you have an 82, do you have the original spring actuated flapper in the airbox or the newer vacuum activated flapper?

David

[Toonces]

Yes, that's a bit of important information I left out. It's an 83 and the vacuum flapper is there and works. But will check it again when I remove it to get to the carbs.

[The Prophet of Doom]

There was a carb tuning guide posted here some time ago that suggested checking the air bleed filter for blockage to avoid 4500-5000rpm stumbles

[Toonces]

Yea, I checked that too last time the carbs were off but for sure I'll check it again.

[QBS]

My and my old time riding partners' '83s' both exibited the random stumble you have described.  Right around 5k rpm under light load in top gear.  We never did figure out a cause and just lived with it.  However, neither bike was as bad as what you report.  I will say that it did seem to sometimes (but definately not always) be associated with the very initial and gentle application of throttle.  4 to 5 k rpm in top gear is in the low speed to high speed circuit transition range.  Which might have something to do with it.