Hi, Adding my pennyworth !!! The oil seal on the cam does in fact cause symptoms as you describe as Ive seen it many times. I agree with Peter however that you should take it back unless you did it yourself of course!! Check to see if new bolts were included in the deal as these stretch when tightened and torque settings are usually a set figure plus a number of degrees turn after that. Its the pulses i cant figure unless your positive ventilation is totally blocked. Cheers Nige