Your positive it's not too lean? Usually when they are set too lean they won't prime very easily. I never had any issue's with a OS not priming up real easy. I'd say richen it up a tad and see how it primes. If you have 0 air leaks and it's not set too lean it'll prime right up.

Also you can try posting in the [link=http://www.rcuniverse.com/forum/forumid_133/tt.htm]OS direct support forum[/link] and see if they offer any advice on what the issue can be.