Hey Pat, what exactly did you do to the exhaust that you fixed. I have same bike, and have spooge between the cylinder and expansion chamber

I have a 1983 CR480 that I run wide open for as much as 3 minutes on steep sand hills. I've been running AmsOil at the recommended 100:1 ratio for over 20 years with no problems. There is less oil going through the jet, so that means that MORE gas is going through the jet. At this ratio, I had to lean the jetting slightly.
I also have a 1986 CR500 that has been running the same mix for 15 years, a 1986 Suzuki 250 Quadracer that I bought new and has been using the same mix, a 1993 Banshee running the same mix since I got it in 2001, a 1987 CR250 running the same mix since 2007, and a 2000 CR500 that I just got and it runs fine one the same mix.
The CR480 was the only one I had to change the jetting on... and I think it was only the pilot jet.
The guy that had the CR250 before me was running Golden Spectro and the AmsOil is actually cleaning up the mess that the Spectro left.
I did a test with 2 identical CR480's in 1984 when I first bought the bike. My neighbor and I raced Fish Canyon at Ocotillo Wells and then we gave the engines the highly technical "spit test" (spitting on the engine fins). Both bikes were so hot that the spit immediately flashed into vapor.
We went back to camp and emptied the Spectro out of my bike and put in the AmsOil at 100:1. We than went and raced Fish Canyon again. Another spit test and his bike (running Spectro) flashed into vapor again. When we spit on the fins of my engine, however, it just sat on the fins. We couldn't believe it and started spitting on my engine. It was dripping with spit and never vaporized any of it. It must have been 40 degrees cooler. You couldn't even stand next to the other guy's bike it was so hot. I'm sold on AmsOil.

One more thing I should mention: I finally opened up the CR480 after running the same piston for 20 years. The bore was so good that I just put another same size piston in it with new rings, wristpin, and bearing. That was in 2004 and it is still running great today.
One thing that should be noted is that AmsOil changed their formula, and I'm still running the old stuff. I haven't tried the new formula yet.