ORIGINAL: Mr Cox
ORIGINAL: Konrad
Opening up the air bleed limits (deteriorate) the engine's ability to draw fuel fuel from the tank. This is why the Fox line of engine is so superior to some of the popular asian brand entry level engines. As all Fox RC engine come with an auto mixture carb of some sort, even the little Fox 0.15 BB R/C. They all draw fuel better than any true air bleed carb at idle.
I don't understand why you constantly have to keep picking on other brands all the time, are you even running any of the small glow engines yourself?
There are even engines that are smaller in capacity then the Fox .15, they are made in asia, feature true ABC and have twin needle carbs etc.
Back to Fox, there are two obvious design flaws on the .15BB model as I see it. The head with a poorly fitted regular glow plug, and the poor design in the inlet area of the crank (ends forward with the threaded prop bolt). It is still a fairly decent sport engine though. The best running engine on 80/20 that I have seen in this size-range is the Webra 1.8cc Speedy, but it also features a glow head rather than a glow plug.
I mentioned no brand. So how can I be constantly picking on other brands? I do bring to the forefront the limitation of the products/designs regardless of the brand. I do this in an effort to increase the understanding of the product/design. The more someone understands the product/design the better it can be utilized! I mentioned "popular Asian" as a way to encompass the entry level engines from Enya, Thunder Tiger and OS. All three manufactures make entry level engines with true air bleed carbs. Again I wasn't trying to single out any "BRAND" I am aware of many fine engine from all around the world that are smaller and even more advanced. I'm thinking of engines build for the FAI F1J 1cc class.
Back to the FOX why pick on her? Most engines have the crankshaft bore machined to a flat bottom. It cost more money to sharped a fully radiuses cutter. I think I mentioned these issue before in this thread. Rossi and many high performance brands have been using radiused cutter for a long time. ( I'm writing up a post to show the how of the FOX 10 cc crankshaft from the Hawk to Eagle IV. I will cover this in detail) As to the head, Fox has made many head shapes for the little 15 BB. (I liked the FAI High Compression trumpet head) The issue you state is common to most FOX heads. It was done on purpose to allow the user to custom fit (lap the glow plug seal area) to ones desired fit. This is a much better way to accomplish the desired placement of the glow plug than the use of shims under the glow plug. There really is no defined definition as to what is the "best" fit. But we can agree with a lot of what doesn't fit. We agree that the "glow button head" is superior. I also like the Nelson/Glow Bee tapered sealing glow plug arrangement.
All the best,
Konrad