I've been running a Pro Circuit T-4 full exhaust system for approx. 2 years. My XR650R had been making some popping sounds on de-cel and and I was assuming it was possibly at the joint where the muffler can and the mid pipe connect. Lately, I've basically have only been using to ride to work and back - approx 14 miles round trip on HWY 78. Last week she wouldn't idle. I've also have the Edelbrock. OK, Maybe the Edelbrock was getting gummed up? I was taking the gas tank and shrouds off and noticed a bunch of black carbon deposits on the back of the left radiator. Took off the header pipe and the exhaust flange of the header that fits into the barrel fell out and rolled around my garage floor! The weld of the pipe to the flange had completely broken!!! I'm going to assume that I fried the left exhaust valve as my compression seems to be rather "low". I need to get in there - got late and had to stop last night - anyone know what I should expect to see or better yet, know what all I should look for in the way of extent of damage? I have contacted Pro Circuit and they are going to fix my pipe. So I am very happy with their customer/product support. If anyone has any good tips or insight it will be appreciated!