I noticed someone has been searching this site for information on this topic. If you have just done or had work done on your Honda Recon 250 ATV or it has been sitting long enough for mud daubers to nest in it, and it runs well other than the fact that it stalls going uphill then you need to check the upper vent hose on the side of the carburetor that runs up to the steering head area. If this hose gets pinched shut or plugged up it will cause this to happen because the trapped air prevents the float bowl from refilling when the atv is on too steep of an incline to vent through the bottom of the carb. Just find the rubber hose that leads from the left side of the carb as shown below. The other end should be up near the steering head and completely open to the atmosphere. Make sure that it is not routed in such a way that the fuel tank pinches it shut when the tank is re-installed.

If you are trying to sort out why your Honda Recon stalls going uphill or any other problem you may be having with it I highly recommend a good service manual. If you are doing your own work it will save your ass a lot of trouble.