An update of where I am.
I removed the secondary throttle plate, installed a Delkevic slip on, a KDX snorkel, and a PCFC.
I have a temporary setup to log a WBO2, RPM, and TPS. Finally got some decent weather, and was able to get a few tuning runs in.
I ended up adding quite a bit of fuel with the throttle more than 60% open in the range expected with the secondary throttle removed.
I don't trust a butt dyno, but seat of the pants midrange is good, feels much snappier than stock. Based on the fuel added and the fact that the factory tune was likely rich I would say looking at a 25 to 30% increase in the 5k to 7.5k area. AFR at WOT is very close to holding 12.8 to 1, assuming my stuff is good and reading correct.
I have a screen shot of AFR vs rpm for 80% throttle and 100% throttle, plus the PCFC screen showing where in the map the fuel was added. I think removing the secondary throttle and adding a PCFC is a good bang for the buck. Looking forward to testing on the trails, got another 6 weeks til thing thaw and start to dry out.

 

Now we're getting somewhere !!!!!!!!!!!!!!

Once you have verified a straight line 12.8:1 at all RPM points while at WOT, you should see huge power boosts in off idle thru 9000 rpm..

 

Outstanding!!!

 

@Nigel , considering the huge power unleashed with a lidless (Carb'd) KLX, you really won't know what's possible until you yank off the airbox lid - and retune the fueling curve for the added airflow.

However, a well done map for the "KDX Snorkel + Slipon" mod combo is also quite "valuable"..

 

BTW, regarding a "Lidless + Slipon" fueling map.. Once done with it, and fueling targets hit, a dyno chart would be the icing on the cake !

I got $10 on 26'ish hp..

Then someone need to let you borrow a full FMF system to add to the lidless airbox - I'm thinking 28'ish hp ...

Notes:
Stock is 23 hp.
The real difference would NOT be in the peak numbers but in the elevated power curve over stock at all rpm points - which would achieve serious gains over the stock detuned midrange - creating a "whole new bike" to ride..
Carb'd KLX250's go from 19-20 hp to 24+ with proper fueling on a lidless + Full FMF mod combo.

 

I'll guess more than 26 hp.

Mine dynoed 25hp @ 9,100 rpm with a stock airbox/lid/snorkel, NO tuner, and a slip on as the ONLY mod.

 

Questions for you; do you run your bike with the O2 sensor or is it deleted like my bike? Someone told me that if you have a PCFC I should bypass the O2 so I did. I also went with the Yosh pipe and added a baffle to quiet it down a bit and its a good sound. And did you have to remove the throttle body to get your STP out? I had to completely remove mine to get that nasty screw out of there but in hindsight I was thinking maybe you can remove the air filter and go in through it with a good screwdriver and the right JIS bit. Thanks.

 

Would be fairly easy to get a couple runs with the lid removed once I am happy with the state of tune for current mods.
I am still a little fat in some areas, which is safe but may be costing a little HP. I am very satisfied so far with the changes. Bike runs well, definitely pulls harder from 5k to 8k rpm.
I can post the difference in fueling to hit the same AFR 12.8 to 1 for the lid removed at some point. For hitting the trails though I will be keeping the lid.
My sensor has some miles on it already, so it could be a couple of points off. A dyno with a calibrated sensor would be a good check but I don't know of a local dyno. I may be upgrading the wbo2 on the car, so if I do that I may hook it up to the bike first for a double check.
Weather here is going to be crap for a while again, so will be a few weeks before I do any more tuning.

 

For the tuning, I am using the dongle to do the o2 sensor delete. Something that is interesting that dynojet does not say a lot about, maybe due to emission regulations, is some of the PCFC tuners have an O2 sensor "tuning" feature. The euro PCFC I have has this feature, the US 300 dual sport PCFC does not. I may try it out. I think it simply biases the O2 sensor signal to make the closed portion richer or leaner. I plan to hook up the sensor signals before and after the PCFC to the logger to get an idea of what it is doing. I may then go ahead and run the factory O2 with the PCFC. I wish I knew more about the factory ECU, it would make it a little easier to implement this feature.
I removed the airbox only and was able to get at the butterfly retaining screw with a small ratchet driver and a screwdriver bit in a socket. I actually put a little pressure to tighten and loosen until it broke free. Was very careful with the force I used.

 

I don't know about peak on my bike, but midrange is UP