mid range issue

i recently installed a cvp stage one carb kit in my 2006 xl1200. im running a hurricane air cleaner and vance and hines slip ons. i live at 2000' elevation.

im getting a slight stumble at 4500 rpms. if i accelerate through, i do not notice, but if i try and cruise in the 4000-5000 rpm range, like through curves aggressively, it is noticeable. i was able to elliminate the stumble by adjusting the idle mixture screw to a leaner setting, 1/2 turn out from seated. however, that caused my idle speed to drop leading me to believe im now running too lean on the idle circuit.

i think my main jet may be too large but i would like some input before i go chasing my tail.

No way the stumble is ignition related? Plugs are ok and gapped to spec?

I have not replaced or checked the plugs recently. I will try that and get back to you.

Can you explain how the symptom I described would be related to the plugs?

I was thinking it may be a coil breaking down at times when at a certain load, made worse by old plugs. Cheapest and easiest place to chase gremlins is with a good set of properly gapped new plugs as your baseline. 1st step to any diagnosis is start with basic tune up items in good state of repair, then go from there.
JMO.

the bike is relatively new to me and low milage (9,000 miles). i have put about 4,000 miles on it since January. if the hessitation/stumble was there prior to the stage one upgrade, i did not notice it.

if the cvp kit has a 99% sucess rate, i will look at the ignition or timing system as a potencial culprit. my understanding is that the timing is a bit over advanced from the factory. but if the issue is a $10 jet i figured i'd start with that.

following roadster guys advice, i installed a fresh set of plugs, which ironically, i ordered with my cvp kit to get free shipping. the plugs definately helped but did not eliminate the issue entirely. i was however abke to bring my idle mixture screw back to a 1 1/2 turns out +/- setting without making the stumble worse.

the stumble is always at a very narrow rpm band, 4500. i thought it may be the point at which the main starts to play a lager role in the overall fuel metering and i'm lean or rich at that point as im transitioning off the needle jet.

the needle does not have grooves for clips. i can add washers under it to lift it. i'm not sure how i would drop it.

i shimmed the needle .020" and had some improvement. then i shimmed it .060" and its running great. i have not had a chance do any plug inspections yet.

thanks for the assistance.

Glad to hear you rectified your concern. Ride safe.