Has it got the right size pistons?there are 3 different size barrels identifiable by the letter A,B,or C stamped somewere around the bottom of the barrel ,there should be a letter printed on the top of piston but its usually burns off but ive washed off some old pistons and its still been there.Andy should be along soon to tell you how to measure the pistons the were the tec info is for pistons sizes( because hes good like that)