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I have a 09 250x, installed a 250r head and cam, opened the air box up about half of Hondas line on the box, full fmf exhaust, twin air filter, I live in 1000' area, about 90 deg is the hottest I usually ride in. I am currently jetted at:
185 main
45 pilot
5th clip on a dyno jet needle for a 250x
fuel screw is at 2-1/2 turns out
boyseen qs3 at 1-1/2 turns

my main question here is, is the 250x carb completely compatible with the r head and cam? I have a slight hesitation as I try and snap the throttle, it seems to run fine if I roll on the throttle slow. same results in all gears and power demands. once the hesitation is over the bike takes off like a bat out of hell. is it possible that I might need to change the emulsion tube(needle jet) and needle with a 250r's parts? Ken this is mainly directed to you seeing as you have probably the best info on this topic. please help, I feel I have split my head enough on this thing. I have had every jet from a 130 main to 185 in this thing and back, something just doesn't seem right, carb has been dipped, blown out spotless, floating valve is replaced. float level is good ap has been rebuilt to, everything double checked also to be correct. some tips please.

Running a very similar setup...
'09 X, '09 head, '08 cam, JD red 5th clip, blah, blah, blah.

Biggest difference is the piston (unless you went to a 13:5) and altitude. We ride ~4k-10.5k feet. Jetting is 45/165 with 2.5 on the fuel screw.

So to answer you direct question, a properly tuned '09 X carb is completely compatible with your R top end.

I just re-read your post. By 1/2 open on the box, are you saying you opened the top only half way, or went to the line on the top but did not do the side (thus calling it half open)?

I have the top opened all the way to the line, but did not cut the side.

half of the cutout on top, I wasn't sure about taking all of it but I think I will now. do you have the pink wire done? I just wanted to make sure I wasn't missing something with this carb. this hesitation is annoying.

I did the pink wire even after being told it would not change anything on the '09. It did not change anything

You can eliminate the airbox as an issue by taking the door off and riding it. If it goes away then cut-away.

If it is running well except a bog/hesitation on the bottom then I would guess it is the adjustment on the leak jet or you need to drop to a 42. The leak jet is not something that can be adjusted on the stand; you really need to take the bike out and nail the throttle creating a load to dial it in (you may already be doing this).

If you have more than just hesitation on the bottom-- slightly hanging idle, flat spot in the power band, etc. -- regardless of how small, then I would check the common stuff that can go wrong on a carb rebuild: make sure the o-ring for the fuel screw went in straight, throttle plate gasket is on in the correct orientation and not warped, diaphragm is no upside down.

Your main jet is way rich. Try a 160.
When you create these hybrid crosses of different bike parts, you become the test engineer.
I used to do that, and finally just had the A/F mixture measured on the dyno. It's not expensive compared to what you spend in time and parts, and it measures your jetting and settles the confusion.

When a 250 isn't enough power, I recommend the 450 upgrade. It solves all of the aggravation of trying to tweak a 250.

I was working with jetting specs from a R, there stock with a 180 main. I am going to try a few more tweaks here. how much does it run to have the dyno done? I went with the 250 because of the wt. and flickablility in the tight woods here. 450 is just to much wt. for me to toss around here. if I was on the track I would be all about it. I just wish Honda had a 300 two stroke. but the 250 is a good solid bike. mabe I just went too far, I think ill start back at the beginning. take the carb of and triple check it, lean it out and try try again. it just gets discouraging when it doesn't seem to work and you know you gotta come up with something else. thanks guys

160 is WAY lean for your setup. 165 at altitude is barely big enough (2.5 on the fuel screw).

At your altitude your 250 will rage just fine. My sons has more than enough to haul my sorry rear up pretty much anything at 5k feet.

On the weight side, you may have been mislead a bit. The 250X is not much different in weight than the 450X, and the 250X weighs more than-- e'hem --my 450 XC-W. The characteristics of the bikes are just totally different. My son can drop me like a bad habit on tight or sudden turns, where I can make him feel lonely and unloved in the bumps or very long up-hills. It all about trading this for that.

wow I looked it up and your right about the weight, I rode both bikes at a dealer and the 450 just seemed like a tank to me. given im used to two stokes, and this is the first four stroke bike I have owned since I was like 12 I had an xr 100. but on another note, why is there such a big gap in the jetting from the stock r specs to what your running on the swap to the X? Also you said before about the pistons comp. ratio. If I remember it was a stock R replacement from vertex, I think it was 13.5:1. that number alone kills me, I remember when 12:1 was up there and you usually ran it on race gas. I mix my fuel 50/50 vp race gas with 93 pump gas.

I am not really sure how the stock R runs at our altitude, so I cannot say if it is good, lean, or rich. I can say that 165 is on the edge for 4k feet, but we frequently go higher which is why I keep it that way. At 10k feet, we are closer to 1-3/4 on the fuel screw. Running a 175-180 would likely be a bad thing for us.

I guess what I am saying is my sons bike probably should be running at least a 170 to get the fuel screw to a respectable position for about 3/4 of what we ride, but the way it is gives us no headache if we change 6k feet in a single ride.

Have you tried running without the VP blend?

I have ran it on only 93 and it runs fine, the fuel here tends to have high ethanol contents. I clean my lawn more carb twice a year because of it, because mostly I forget to add stabilizer to it. so I am only running my fuel this way to keep my motor as clean as possible and because I have fuel phobia's messing up my bikes carb. lol. for vp here i pay about 70-75 bucks for 5g's that's also what I pay for a case of Honda oil too. I love the power delivery of the r top end, very happy with it if I can just finally get it spot on. i will probley back step to a 170 and so on, and change my pilot accordingly.

I run a similar setup on a 06 250x first thing do the o ring mod on ap pump and adjust the ap timing so it just clears the carb slide and shoots straight down the head. on mine the fuel stream was hitting the carb slide timed it problem solved. bike flat out rips for a 250x

09R head ported
08R cam
13.1 piston
air box open, top only
q2 ap with o ring mod
fmf Q4 & megabomb header
main jet 172
pilot 45
leak jet stock 50
fuel screw 1-1/2 out
neddle men-16204-671 3rd clip
pink wire no

'09 has the updated carb. A/p, o-ring mod does not apply.

I had known about the update, my carb requires some sort of special tool to adj. the timing anyhow, not worried about that. I had went with 160 on the main, im third clip on the needle. im going to try one more clip up on the needle yet as it still has a smudge of hesitation off idle and I couldn't get rid of it with the fuel screw. the main jet change made all the difference in the world.

Interesting. I am not sure how you are not turning the spark plug into a cinder with those settings.

What compression piston did you put in?