I have a esr310pv motor stock stroke crank (88) curtis sparks pipe, boyesen rad valve and a 38ml carb. I have read countless posts saying that people are running 175-18? Main jet, i am at 300ft above sea level and i cant get mine to run any bigger then a 158 main. Any bigger and it crackles top end and fouls plugs, the plug is perfect in colour and have done countless plug drops. Is this a problem?