Flat top end, hard to plane out

Sean 66 · Jul 29, 2020

2004 5.0GL Volvo Penta (305 vortec) runs great in the driveway, but really struggles to get to top end. Timing is set correctly and advances with throttle increase. carb rebuilt and tuned ( i increased the jets to 78, and installed a new 5.5 power valve. 20 lbs of vacuum at Idle of 700. , I dropped a size of prop to get a better hole shot, which had some positive affect. New plugs, cap and rotor, new water pump. If given enough time it will reach a plane at 32 MPH and 3800 RPMs, but it takes forever, and wont happen on a choppy sea at all. Please anyone? thank you.

saf · Jul 30, 2020

I am not an expert by any means but I had a similar problem. In my case, it turned out to be the ignition module. So, if you have an electronic ignition but do not have an ECU, i.e. your distributor has a 4-wire plug that is not connected to anything, you might want to take a closer look at your ignition module and/or pickup coil. As I learned from my experience, these ignition modules can fail in very subtle ways, i.e. the engine would be working fine and even ignition timing might appear to be advancing but the module would not be working 100% correctly. Check your total total timing advance (you should see about 30 degrees at 2500rpm) and the dwell time (it should increase with rpm). These modules are analog, so, they rely on the amplitude of the input signal from the pickup coil to set the dwell time correctly. If your connector from the pickup coil has rusted, it might affect the dwell setting.