I have a Topeak MMB 2 Mini Master Blaster that does not seem to work right. It will pump a little air but not well. When pulling it open (intake stroke) there is quite a bit of resistance like it can not breath in. It only seems to "inhale" for the first two inches of the stroke and not for the remaining 4 inches. I pulled it apart and did not find anything obviously wrong. The Topeak support web site mentions a "check valve" but I do not see anything that looks like a check valve. Any suggestions?