Hi all - jeep has been running well and I've been getting it out quite a bit recently, including some high elevation runs (say over 13,000 ft). As I live in Denver at 5000' (but the carb is jetted for 7500' as I spend a lot of driving time around those elevations) I do some carb tuning throughout the day as the elevations changes from 5000-13000'. Obviously in a perfect world, I'd change jets as needed, but since that is a bit impractical to me at the moment, I make the 7500' jets work pretty well everywhere and tweak things like timing and idle screws. So, how much additional initial timing advance do you think would be appropriate for elevation change? My rebuilt v6 with 252 comp cam seems to like a lot of initial advance - 9BTDC at 5000' (it actually idles better or stronger with more vacuum with 12BTDC, but I think I start to get too much advance with 'all in' during driving conditions). I usually readjust the carb idle mix screws and initial timing at the trail head when locking in and airing down - generally around 8-9000'. I often bump it up to about 12BTDC. Now that I have been pushing even higher, I am having some issues with idling at over 12,000' and finally pushed the initial advance to 16BTDC, and it ran much better. Reasonable? It likes as much timing as it can get, but I don't want damage. Of course, during slow speed, lower rpm conditions like crawling along in 4lo, I don't think it gets anywhere near 'all-in', and thus running a lot of initial should be safe? What kind of carb adjustments would you expect? I guess I have been surprised as I think of higher elevation needing less fuel (smaller jets) for proper mix. Certainly the smaller jets help, but its the idle portion that I am wondering about. As I climb up to about 10,000' it seems the idle mix screws can be turned in slightly to help lean out idle, but as we push the super high elevations over 12,000', it seems I turning them in more doesn't help, and if anything I need to turn them out (maybe because I am advancing the timing as well it likes the extra fuel). Sometimes a I cheat a little bit and increase the idle rpm screw which opens the throttle plate a smidge and helps pull fuel through the main jets (at least that is what I think is happening). It also provides a bit of vacuum to the the ported vac can which would then advance the timing a bit more. So, maybe what I am figuring out...advancing the timing is more important than too much fiddling with carb idle mix screws or even the idle rpm screw (especially when you aren't changing the main jets). i think the real solution is TBI...but that is another lifetime away.