It seems most of the threads on 125 main jet size discuss sizes in the 170 to 190 range. My 82 RM 125 came from the factory with a 270 main and a 30 pilot. I have removed both jets from my carb, but I cannot read the stamping. I am assuming it is stock, but Im not sure. The manual suggested 20:1 mix ratios back then and i am attempting to run synthetic oil at 32 or 34:1. I ran the bike yesterday at 34:1 and I had an incredible amount of oil spitting out of the pipe. The bike was bogging and not revving as it should. The bike has new Wiseco piston and Boyesen Power Reeds. I realize that I need to rejet. I understand that jetting depends on many different factors, such as rider weight, weather conditions, etc. Where do I start with jetting? Should I start with a 190 jet, or a 260 jet? How much incremental difference do you get from moving a size down? I have a YZ400F and the RM 125 burned about 2 to 3 times more fuel for the same amount of riding.
