07 KX250: Lean condition in whoops, like out of gas

[myckmcclung]

2007 KX250, jetting is perfect, float level is perfect, stock carb is clean as it gets, ultrasonic and brushed. cleaner than from the factory.
All vent hoses are new no pinches, new fuel line, with inline filter, flowing fine, installed to hopefully eliminte the following issue, with no results.
V-force3 reed block, fmf gnarly, T2. no compression leaks.
Here's the situation, and I'm at my witts end trying to narrow it down.
Fast shallow whoop section, in the pipe 4th gear, second bump, goes lean, like I'm running out of gas, I chop the throttle, the slide closes, pull in the clutch, still screamin it's head off, feather the clutch and it drops back down to normal Idle. it only does this in this same condition, smooth straights no issue, only in the whoops, or in a heavy G-out and it is inconsitant, as in it doesn't do it every time, but those are the conditions where it occurs.
I have checked the float height, I have replaced the floats, and the fuel needle, cleaned the seat, all of the circuits in the carb are clean and smooth.
Any issues with crank seals causing issues like this?

[KXDINO]

try raising the fuel level a tad higher, sounds like it starving.Whats your jetting specs.

[sandblaster]

try raising the fuel level a tad higher, sounds like it starving.Whats your jetting specs.

Good advice KXDINO..
If the carb is not the issue... what else could it be?
Gas cap vent plugged or restricted?
Petcock filter plugged?
External fuel filter? Plugged?

Wiring connections
CDI
COIL
Stator
Good ground to the coil
Spark plug wire

What else?

[KXDINO]

that reminds me put the tank breather hose the wrong way once didnt look at the arrow , made it starve of fuel it did.

[myckmcclung]

kxdino 42 pilot 158 main stock needle second clip sea level, 40:1 w 93 octane pump gas and Lucas semi synthetic premix.
It's not the jetting. my float height is good too. had several people take a look at it while I was checking it last time i had the carb off.
At this point all I can figure is a bad gasket at my air boot/reed valve.
I am doing a topend on it next week, will do a leak down before I tear it down, I am praying it's not a stator side crank seal.
As I said this is an intermittent issue.
One place I ride, it does it in the same spot(section of the trail,[the top of the 2nd whoop, on the top of 3rd gear]) on the trail when it happens, but it doesn't do it every time I go through.
when it happened over the weekend, I pulled in the clutch and shifted to nuetral,let the clutch out to turn the gass off, then back on, tried the kill switch,  the throttle was completely closed, and it was still screaming, for at least 30 seconds, until I pulled in the clutch shifted into second gear and fanned the clutch a bit, once it  had a load it calmed down and idled normally.

[KXDINO]

All you can do is go threw a list to check , i know on my kx250 over here in australia at sea level on the sand tracks , that jetting with that 93 fuel would melt the motor or have a serious detonation problem, even with the 98 with richer jetting was a problem , i ended up useing a vhm custom head volume as the barrel was machine .4 mm to get more grunt as well as a port job and all the other tricks i could throw at it. the vhm head is tons better then oem. make sure the crank sensor air gap is set .45 to .85 mm i set ours on the big side. Hope you find the cause of your grief as i would like to know what it is to.

[myckmcclung]

my parts are in, I just need a day off to do the work now. 

[kawrider]

2007 KX250, jetting is perfect, float level is perfect, stock carb is clean as it gets, ultrasonic and brushed. cleaner than from the factory.
All vent hoses are new no pinches, new fuel line, with inline filter, flowing fine, installed to hopefully eliminte the following issue, with no results.

Here's the situation, and I'm at my witts end trying to narrow it down.
Fast shallow whoop section, in the pipe 4th gear, second bump, goes lean, like I'm running out of gas, I chop the throttle, the slide closes, pull in the clutch, still screamin it's head off, feather the clutch and it drops back down to normal Idle. it only does this in this same condition, smooth straights no issue, only in the whoops, or in a heavy G-out and it is inconsitant, as in it doesn't do it every time, but those are the conditions where it occurs.
I have checked the float height, I have replaced the floats, and the fuel needle, cleaned the seat, all of the circuits in the carb are clean and smooth.
Any issues with crank seals causing issues like this?

I know this thread is over a year old, but i am curious if the author ever found the problem to this? I had the exact problem on my 05 (r1), and through the whoops also. I also replaced everything he did as well. I was going to alter float height as a tuning trick, but i never did out of fear of other issues coming up (i was about done with that carb at that point), and of course rejetting it. Eventually, i switched to a lectron carb, but i raise this up for any future readers and also, i hope he got it figured out and what the problem was. 1 thing i did learn from a yz page was about the jet block gasket. I'll admit, ive been in a bunch of these carbs, but i never touched these before. I bring up this, simply because i never tried it, but to also bring on potential discussion.

https://thumpertalk.com/forums/topic/1235219-2005-kx250-jet-block-gasket-of-course-its-different/