Rebuilt my powerhead a couple years back and it has always had a fluctuating water pressure at idle and at first part of throttle, then goes steady after about 1500 RPM. I have had no issues with engine until just last week when I put in a new water pump impeller. I now have 13 psi at idle and still the fluctuating water pressure at around 1500 RPM (engine is running in barrel). At 5000 RPM (out on the water) I am up over 25 PSI. I found a hole in my poppet diaphragm, so replaced it, thinking I had found my high water pressure problem. Put engine back in barrel and ran again before taking to lake. Still had fluctuating water pressure and 13 PSI at idle....but also had a lot of dirty oil on top of the water in my barrel and when I pulled engine from water there was dirty oil on both sides of the gear (prop) housing. The oil felt like it had fine sand in it.... maybe carbon deposit form exhaust??? Any thoughts on what is wrong?