Could be the big end bearings possibly mate if yout hink its engine related?

personally if your not sure if its chipped etc i would do as i said above and remove the bleed valve and keep the amal valve. SOME chips the amal valve is removed, some not. . .!

bleed valve sounds dodgy, it should increase boost, but dont fook about with it as you dont know if its gonna fuel enough if the boost does increase! imo best removing it all together and leaving it to an expert!