> Running an engine to rich does not burn valves. Well, without putting too much of a point on it, you're quite wrong.
Running rich not only creates deposits that get lodged between the valve faces and seats and allow the combustion gasses to blow through and burn the metal, but these deposits also prevent the valve from cooling which it does through full contact with the seat. About 75% of the total valve cooling comes from full contact with the seat. If it can't fully seat it's easy to understand why the result is a burned valve. Along with these issues, the unburned deposits resulting from a continuously-rich mixture also build up between the valve stem and its guide eventually impairing the free movement of the valve. The spring eventually loses its battle with the stem/guide friction and at that point the valve can no longer fully seat. This struggle between the spring and the valve stem/guide also contributes heat to the mix. All of this is part of the same process, and it comes from continuously running rich. If one doesn't have a carb with a mixture control I suppose one is stuck with taking the heads off at frequent intervals to clean things out. Early planes and early carbs didn't have mixture controls and in those days it was normal to take the engines apart frequently. I've found it valuable to treat my converted VW engine as I would an aircraft engine (which, come to think of it, it is isn't it!) With that in mind, in the current issue of Sport Aviation there is a good article by Mike Busch on using CHT instead of EGT for leaning. In addition, there is a wealth of information out there by John Deakin, Mike Busch, and the late Bob Hoover. I think even Langford has written on this subject. Old timers' wagging fingers aside, there's no excuse these days with our internet access for not understanding how destructive running an engine continuously rich is. Here's some good links: http://www.avweb.com/news/pelican/182155-1.html http://www.avweb.com/news/pelican/182084-1.html http://www.avweb.com/news/pelican/182132-1.html Richening the mixture has its place - on takeoff and initial climb and anytime you're running above 75% percent power and need the fuel for cooling. From what I've seen though, there are many really badly informed pilots who never touch their mixture controls and fully expect to have to take the heads off every 200-300 hours and clean out all the black stuff. It's what they "learned" from some other ill-informed person and they've never questioned this "wisdom". Thanks to the easy access these days of new and good information that some very smart people have been kind enough to provide for free, there is no longer any excuse for adhering to the practices of the ignorant. That being said, everybody ought to run their engine as they see fit. You'll get back exactly what you put into it. Mike KSEE ____________________________________________________________ Globe Life Insurance $1* Buys $50,000 Life Insurance. Adults or Children. No Medical Exam. http://thirdpartyoffers.juno.com/TGL3141/4cd08bc96425a1c400m04vuc
