I've been running a qjet for 30+yrs and have no reason to change. I've laid my other 40 on its side a couple of times and I'd have to turn the engine off. If the nose of the 40 is drastically pointing down, like coming off a ledge it'll idle ruff. I might have to feather the throttle a little. I have have couple of minimal tweaks that I do to them for offroad. I'm still learning to fine tune for better economy and performance. In the past I'd go to an a/p store and buy one for a certain application and they work great out of the box and are inexpensive. I've found with those type carbs, the internals are very generic and designed to work on several applications. It's difficult to id the internal parts because they're not marked(jets & rods), so it's hard to really fine tune them. Anytime I see a qjet for free or real cheap I'll pic it up for parts or possible rebuild. I recently found an unmolested stk carb I'll be building. I'll baseline it and then play with it. I always keep a rebuild kit handy.