Hello all I have just got a 1997 Royal Star that has 40,000 on it.......it has a popping at a steady RPM so I decided to do a compression test so I found the right front is 51 PSI the right rear is 75 PSI and the left side are both 99 psi I have no records of maintenance so I am wondering if it's because of carbon buildup that is common with these bikes or is it rings or possibly the valves need adjustment thank you in advance for any help troubleshooting my issues.......Chuck73