I know this is mostly an auto site but i was hoping someone might be able to point me in the right direction, so here it goes. I have a 20' cuddy cabin with a Volvo Penta AQ120B motor. it is basically a marineized version of a b20. I think it's 2.3 liter. It has a single solex sidedraft carb that has been rebuilt. My probblem is when running as cruising speed (4000-4200 rpm) the engine will just loose power. Like someone is cutting off the gas or pushing a kill switch. If I back off the throttle it will usually not stall and recover. If it does stall it always starts right back up after just pumping the throttle once. If I keep it at 3500 rpm it does not do it at all. the closer I get to 4000 rpm the worse it gets. It also seems motion sensitive. Like when the boat rides over a swell, it will cut out for a second when pitching down the wave. On flat seas I can run over 4000 for a few minutes but it always ends up cutting out eventually.
The only part of the fuel system that is not replaced is the fuel pump. I also still have points and am looking in to converting to electronic.

Car Folks....please help.

PS....it is not the most powerful motor I have ever had in a boat but runs very solid (other than problem described above) and always has gotten me back to port. Go Volvo.