SFO, you're right, they did de-tune it. They had way to much compression, so you had to jet it rich to keep from pinging, but then it would burble BAD!! Once I had my head done, I could drop my jetting quite a bit and it wouldn't ping. The shop at the time also sanded my needle a hair to richen it through the middle. The shop used to be called Kearny Mesa Yamaha, in San Diego. The shop is no longer there, but the owner has a hop-up shop called KMY Motorsports, in El Cajon. I'm willing to bet he still knows alot about the old 490 motors, and could help you out. If you can't find him, contact Precision Concepts, also in El Cajon, Ca. They do alot of work together, since the owner of that shop used to work for Kearny Mesa. I don't know their number either, but he runs an add in most of the mags, and he has a web sight, so I'm sure you can find it.