Tam, the reason you are getting less smoke at full power is probably due to the pump having to overcome the pressure difference of the exhaust stream versus ambient air pressure. Same goes with a turbine fuel pump. At full power model turbines develop anywhere from 20 to 40 psi of case pressure. So at full power a pump has do deliver somewhere close to (other factors are included like lube, chamber pressure drop, etc etc that change as well)that value plus more in order to get a positive flow rate and keep the jet running. One of the reasons turbine fuel pumps have to be able to pump at higher pressures.

Andy