Another jetting issue(imagine that)
 

Yes, I went through the normal searches for info:( I purchased a 2003 EC250
from a forum member. I love the bike, and todays shakedown ride produced some results that met or exceeded my expectations. My issue...Early morning start-up left me at a loss. It would not run at all hardly, from idle to somewhere near 1/3 throttle. Even after warming up, it exhibited the same throttle responses. I massage the throttle and headed into a nearby WOT type runout stretch of trail. Once I rolled it passed the ugly, and got 1/2 throttle & up...She came to life, and surprised me by immediately lifting the front tire, and flat out got with the program. It ran like that all the way through the top gear. After throttling back for the return trip, she produced the same poor bottom end performance. That is, 'till I wound her up, again. I pulled the plug, it was grey in color(dry{BR8ES NJK}) I swapped in a BR8EG and headed out. I figured out in short order that tugging the choke part way closed cleaned up a lot of the part throttle issue. After a lovely 32 mi. flog, I pulled the plug(wet, but almost tan in color). My issue is, I'm not sure what to start with, since I ran the bike with the choke about 1/2 engaged to produce the finishing plug condition. The specs provided by my bike's former owner are as follows:
170 main
42 pilot
#8 slide
CCK #3
I assumed I'd have a jetting issue, as we live and ride in different climates. I typically ride in winter 0'-2500' elevation, Temps 30 F-60 F very high humidity. I'm not 100% sure of fuel type, but the mixture is said to be 44:1. I would be using 91 octane pump gas at 40:1, for a nice round figure. I'm a quick study, would like to resolve this quickly. I am looking for any advice on a how or what to do first. The choke thing sort of has me stumped, as I may have to change everything, or not...I don't know. Thank you.

When you ran it in the morning I assume the choke was off. Would you say that the bike felt flat and lacked power, and that throttle response improved greatly after semi engaging the choke? If so, which is how it reads coupled with a grey plug, you are leaaaan.

The main strikes me as being super lean for the elevations and temps you have stated. I'd be thinking 180 minimum.

You also have a lean slide, with a 42 pilot in a 250.

Without any knowledge of the older engines or experience jetting one I'd be looking in the DB section for someone similar. I'd be looking at starting with fresh fuel mixed at a known ratio. The needle in clip #4 and a 180-185 main. I'd then go about establishing the idle circuit ala pilot jet before moving onto the clip position, and then the main.

Upon cold start in early AM, She smoked like a house on fire, and did not want idle w/o a little help. A bit of warming up, and choke off, a slight twist and she bogged...bad. Definitely a dry grey plug(BR8ES). The finshing plug color(BR8EG) wet but close to a perfect tan color. Upon purchase I assumed jetting could be an issue, I'm ready to get into it. Thanks for the starting point. I'll document any changes/results for future reference. Thanks again.

Have you checked that the pilot jet is not blocked, had a similar experience with a guy on a ktm

Cold blooded (takes ages to run without choke) is also a sign of being lean. Once you get it running it'll run hot. Like Matt said it could be as simple as a blocked pilot jet, but for sea level, cold temps, a number 8 slide, and a 250s signal, and that it continues up to 1/3 throttle I'd think lean needle. The 170 sounds lean too.

This is assuming that its not pulling gearoil through the main seal and the previous owner has tried to lean it out in an attempt to make it run better. If this was the case though it would definitely get worse running with the choke on (or half on).

Today is a busy day, but I'll pull it apart tomorrow and verify what's in it, for sure. Then have a go at correcting it.

That looks really lean to me, and your plug being grey backs that up. Was that carb modded by RBD? I know he likes to cut the slides to #8 and use the C series needle, but on a 250 near sea level it scares me. Make sure the carb is clean and try a richer overall setup. You can try the same needle, or a DDK, but go up to a 180 main with them and try to get a #7 slide. I never saw a 250 that needed a #8 at your elevation.

my 07 250 came from houston.. close to sea level
rb carb mod.. 7 slide (no idea if it was cut tho ) 45 pilot, 182 main, cek needle ctr clip i think..

I can't comment on the needle you have, but I tried a #8 slide in my carb and it was too lean.

I would almost guarantee that you would really like the JDBlue in that bike, enough to end the jetting fuss. RBD doesn't replace the slide, he cuts them, so if its marked #8 it was not from him. Get a #7. That bike sounds like it was set up for high altitude.