Ok my cruiser has just developed a rough idle. Plugs are good, wires are good, good distributer cap, good rotor, good coil. So I pulled out the trusty vacuum gage and this is what I found. A steady 5 hg of vacuum. My haynes book says it should be 17 hg. It does not jump around just a slow steady 5 hg. I checked the timing about 6 months ago and it was fine. I also have a problem with it backfiring when it's cold and pinging sometimes around 2500rpm. Are these problems related. ??? I need some direction.