Could be.. :p

The point at which the first taper starts depends on clip position and the particular needle.

For example, I just measured the NOZJ that I have here by the desk. Its a half clip leaner than N1EJ. Not counting the clip section. Just the effective part of the needle the full length is 50mm. The straight section is only 5mm before the taper starts. Now consider that you will have the slide lifted a little bit to allow for an idle, you only have a few mm of straight section to use before you're onto the taper. All in all for this needle the straight section is only 10% of the equation. By lifting the clip you lengthen it which is why it helps somewhat, but as always you then hit that rich first taper.

I have an 09 ec 250 that had the exact same problem last weekend. When I was fueling the bike, I noticed the gas cap insert shrunk over the winter. I tried to stretch it out to make a good seal to the top of the tank and went riding. When the bike started acting up, I took that insert out and disconnected the vent line from the frame. Bike ran great the rest of the day.

Well just as an update I thought I'd report.

Nothing much to report. Ran the bike a few times (not much riding in winter here), but with a combination of a few things & a CCL needle it seemed to run well. Had a ride in the weekend at reasonable altitude & cold day it seemed a little lean off closed so a 1/2 turn & seemed fine. Were a few uphills & under load sections.

Put my other non dented gutted pipe on & couldn't tell the difference. No problems so far. Although there wasn't much in the way of long up hills on this loop.

No smoking gun, but as long as it runs right I'll put it down to a combination of factors. Possibly the chromed pipe increased pipe temp a bit & required slightly richer jetting so went from borderline to over lean in some area.

Must do my planned head mod to reduce squish right down but retain compression as std (so I can kick it over easily). Its in the queue.