Volvo Penta will not rev above 1500

[DougAnnapolis]

Our highly reliable 2007 Volvo Penta, 40 HP, 4 cylinder, stalled while motoring at 2100 RPM. Could not restart. I changed primary filter - no luck. Towboat brought us home. After changing secondary filter and bleeding the fuel system 3 times, I could get it start, but runs rough. Even a full throttle it cycles from 500 RPM to 1500, then drops back to 500. Will run for 15-20 minutes and then stalls.

Inspecting old filters the primary filter shows a few small black spots but 95 % of filter element is clean. I use BioBore, and FTTP each time I refill. Last big fill-up was in Solomons island and we motored with no incident for 47 miles.

Any suggestions?