What type of prop are you using? Sometimes these photo tachs are not especially sensitive to plain black coloured props (or dark coloured ones generally) I have seen some people put a dab of paint on each blade (it has to be both blades-for obvious reasons!) to improve the contrast.
I have a couple of (as yet unrun) Fuji 099s so I'd be interested to hear what rpms you're getting on a particular prop and fuel. Also have a 15 and a 19. Once upon a time Fujis were a bit on the cheap and nasty side-have you seen what MECOA are charging for Fujis these days.