Flat spot on accelerating

[t20sl@yahoo.com]

I have a 11000 mile 79 CBX. Completely stock except it has 6 onto 6 SS exhaust. Have owned it this way for over 15 years. Problem it has always had is riding down the highway at 60 mph 4,000 rpm if it very gently roll OFF the throttle slightly (not to an idle) and then roll it back on slowly there is a very noticeable hesitation. If I put choke on about 1/3 - 1/2 and try it it goes away.
I would think its lean but where? Fat part of needles? Slow jet? Ideas? Thanks

[steve murdoch icoa #5322]

Welcome to the site.
Yes you mention stock except for 6-6. Just confirming a stock air filter instead of a K&N.
That aftermarket filter produced a small mid-range stumble in my '79.

[t20sl@yahoo.com]

Yes stock air filter. I may have changed mains up 1 size but honestly don't remember anything else when I put the exhaust on 15 yrs ago. Only stumbles when slightly closing throttle and rolling back on gently. Reason I am not sure its lean is when applying choke I know the choke also increases the idle speed so am not sure which is curing the stumble, extra fuel or slides not dropping as much.
Need help in knowing what to change, tired of the stumble.

[daves79x]

A couple of things to do: Replace the stock #65 primary mains with #68s. That should do the trick, but you can also shim the needles .020 inch. Some have gone from #35 pilot jets to #38 also. The first two will likely do the trick.

Dave