I have a 89 XR600 dual sport with a 628 kit that pops and dies at idle. That is the best way I can describe it. It idles along and then poof, dead. It starts right back up but it's kind of embarrassing kicking your bike at the stop light. I have seen this in a stock 88 XR600 thatI used to own, and a 90 XR600 with the same 628 kit, that a friend owned, but the problem wasn't as bad as it is with this one. With three bikes that have the same problem, to varying degrees, I thought for sure I would find something on the internet but haven't so far. The bike also detonates on pump gas when it gets hot, and it, like all the XR600's I've ridden, run hot in the summer. If I run a quart of race gas with a tank of pump, it no longer detonates, but still pops and dies at idle. Octane booster doesn't have any effect on either problem. After trying all the things listed below, it "feels" like the timing may be advanced too far, and it's firing and stopping the piston before top dead center. According to the manual, there is no timing adjustment. I have tried a CDI box off another XR600, no difference. I have set the valve clearances. I have cleaned every orifice in the carburator and checked the air cut off diaphram. I have checked the cam timing by looking at the timing marks on the cam sproket and the T line on the flywheel. I have increased the main jet to a 175 thinking more fuel/run cooler (this was for the detonation problem). I have even hogged out the holes in the pulse generator braket and moved the timing head (just a little) in the direction of rotation to retard the timing (not recomended for the weak of heart). I just purchased a 2000 XR650 so I'm selling this one, problems and all, but I would really like to know what the heck is going on. Also, does anyone have a picture of a passenger peg setup for the XR650? The frame isn't really "modification friendly". Sorry this turned into a novel but I wanted to be thorough.