Fuel pressure drop

Hi there,

I'm building a Kitfox with a Rotax 912iS. So, new build, new engine, and new install. The aircraft is not airworthy yet (that inspection is next Tuesday). While running the engine today, I noticed a drop in fuel pressure as compared to previous runs. Where pressure had been 42-45 psi, today it was 39.5-40.5. The Kitfox has fiberglass tanks, and I followed a thorough cleaning process, but I'm guessing there's still gunk/debris that's getting caught with the filter.

My plan is to replace the pre-pump filter and check the fuel pump screens. 

Am I on the right track and/or are there other things I should look at?

Thanks,

Steve