I originally posted this in the Jetting Forum, but go no responses at all - would really appreciate any insight as to the following: Question for JD or any other TT jetting guru out there: Ride in and around Calgary, Alberta which has an elevation of approx. 3500 ft. Rides are typically from this elevation up to around 4500-5000. Average relative humidity in winter is about 65% - not sure what it is in the summer - but I'm guessing no more than 75% (its pretty dry here). Temperatures currently are about 10-15C (approx 55-60F ??) and in the summer are usually around 20C Have been experiencing mild to moderate sputtering and popping on decel - as I understand it this is either to be expected with a 4-stroke, or may be symptomatic of a lean condition. Installed a WB Carbon-Pro exhaust which I would assume would exacerbate a lean condition, and therefore took to tinkering with the jetting. Given that the popping occurred while off the throttle, I assumed that the first course of action would be to go to a larger pilot jet (stock is a 45). I did this but when I went to kick it over it let forth a HUGE backfire and the whole garage reeked of gas. Was unable to get it to fire. I figured I fouled the plug - but checked it and it was fine, and once I replaced the stock PJ - she fired up easy. Instead I raised the stock needle by dropping the clip to the 4th pos. and went to the next largest main jet that I had, a 178 (stock is a 172). Took it to the track and this setup seemed to remedy any popping/sputtering. I'm wondering now though whether or not it's too rich. Just received the JD jet kit, which suggests a main jet of 168 and the blue clip in the 3rd pos. While I understand that these are merely guides and that actual conditions will dictate changes +/-, does anybody have any recommended jetting setups for the aforementioned conditions? I would like to have the best throttle response possible, but do not want to sacrifice engine reliability to get it (I'd rather be safe and ride a little rich than a little lean), which brings me to my next question: How dangerous is it to run a 4-stroke on the lean side. I have heard that this is more a danger for 2 strokes, but I haven't yet heard a convincing argument as to why this may be so. Thoughts?