914 Fuel Smell in Cockpit

I recently acquired a TL-Ultralight Sting S4 with a Rotax 914.  Before acquiring around a month ago, the plane had the 5-year rubber, new fuel pumps, new carb needles, new floats and carb balance.  I’ve put about 30 hours on it and it runs well.  The last couple flights there has been a strong fuel odor in the cabin, especially on extended climbs.  I checked the fuel lines to the in-cabin cut-off valve and it does not appear to be the source.  I’ve decowled and I don’t see or feel any obvious leaks.  I have a CO monitor and the cabin is good.  I did notice that the exhaust pipe itself has a faint fuel smell.  Any ideas?