diy venturi

[poo-tang]

recently purchased a gen-x 4100 Nw for a diy skimmer i made. the venturi that came with it is useless to me as i don't know how to use it inline, i think it is only for in sump, mine will be external.
i have seen diy venturi designs and could easily make one but i want to know what if any are the ill effects on the pump, or noise even, caused by reducing the inside diameter of the inlet side of the pump. this doesn't sound like it could be good for the pump or its flow rating. does it lower flow rates too?
should i just throw a quarter inch airline on the inlet side without recucing the inside diameter. please enlighten me.