1. ATC200X because it was cheaper on ebay. it bolts up to the stock intake manifold and airbox boot.
2. no
3. Never tried the crf150 carb
4. yes
5. Try tock jetting the carb comes with but with xr100 needle

I run the mikuni vm26 now and made it work with the air box

 

I wouldn't recommend either carb on a stock head with a BBK.

I can only speak for the ATC200X carb, I didn't try the CRF150F.

- I forgot to mention; I ran a TB120 kit, TB 120 cam (some say equal to stock), White Brothers exhaust, lightened flywheel, 1 degree of static advance (relocated the pickup).

If I recall correctly the air inlet side of the ATC carb is larger than stock, so it may not fit. I ran an UNI pod with no issues.

You can reuse the stock XR100R throttle, but not the cable its too short. I believe I ran a CR80R cable and XR100R throttle - I also ran a CR85R clutch lever to help with the pull.

I ended up pulling the ATC carb off and using the 100R carb with a 102 main jet. I'm no James Stewart, and needed the bike to run well all over the range, not just W.O.T. I have piles of main jets for either carb, your's for the cost of postage. If you want to make a notable improvement, talk to terry at firepowerminis - he's got a lead on an affordable high flow head that should make that bore kit sing, as well as exchange lightened flywheels that really help the bike get out of the corner.

 

Was the light flywheel worth it?

 

And isn't the screw cap on the atx200 bigger?

 

I ended up going with a CRF150F carb. Uses stock manifold and air boot to airbox. I also ported and polished the head. Should have it together and running this weekend. Will post updates once tuned.

 

I was able to dial in the jetting and ride the bike today. The gain in performance was more than I was expecting. It rips. Here's the combo I went with...
- BBR 120 kit & cam
- ported & polished head by myself
- full Yoshimura exhaust
- Big Gun rev box
- K&N stock replacement filter
- 2007 CRF150F carb with 150 needle in #2 slot, 38 pilot and 105 main jet (for sea level and 30*F temp)

 

thanks for the info, I'm using nearly the same setup. Only issue I've got is that the conversion frame my xr100 motor is in doesn't have room for the "air-cut valve" that attaches to the carb so I'm going to try removing it and blocking it off.
Hopefully it won't throw the jetting off too much... As far as I can find info, the air cut valve is only to lessen backfiring when throttle chopped.