Hi guys. I've recently bought an older bike - a 1990 GSXR750. I'm use to modern machines and I'm trying to learn about the motor in this one. I bought the manual, but I've come up with some questions. I had a mechanic look at it a few weeks ago. He was going to replace the plugs because they are carbon fouled ( I think the bike is running a little rich). He didn't have the right plugs in stock and said the plugs in the bike were the wrong size for the year and said I either had a 1992 motor or a 1992 head on a 1990 motor. Is that possible and how can I tell if I have a 1990 motor or a 1992 motor. Also the manual indicates the idle knob between carbs 2 and 3, however I have a knob (screw) on a long stem sticking out the side of the motor. I looks like an idle type adjustment to me. And yes I know where the choke is. How do you adjust the mixture. The manual says it is factory set and you shouldn't adjust it, however in the trouble shooting section it clearly suggests that the bike is running too rich. Thanks guys.