Not24
Posts: 999
Joined: 12/7/2002
From: Gloucester,
VA, USA
Status: offline
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Bax is not the one who said to use high nitro. He is conservative with his tuning comments. He says 10% nitro with a synthetic/ castor blend. That's where I got the Powermaster 10% from. He also says 18-8 to 18-10 props that turn between 7300 and 7800 rpm. He recommends 18% oil minimum, and clearly advises to stay away from the low oil ST fuels. All in all, he and ST are on the same page when it comes to tuning advice.
I just tried Googling to find the article that swears by 20% nitro, and I can't locate it. Whoever it is is rather insistant on his recommendations.
About the nitro content for this engine. After all the testing that I have done, I would say that the way you can tell which is best is to go by where your needle valves wind up being set. The low or zero nitro requires a closed needle, and the high nitro requires a very open needle. The closed needle will make for less lubrication in the cylinder, and the open one will allow more. I like my high needle to run best at about 1.5 turns open, which is right in the middle of the adjustment range. This I learned from doing the tests on the flow meter. Anything more than 2.5 turns open gives the same flow reading. If you need to be open that far to run right, you are using too much nitro. This also assumes that the carb is one that does work properly, and has no leaks. This high needle setting is also DIRECTLY related to the size of the venturi. In other words, the nitro content that works best has to be in harmony with the venturi size that works best. In the case of this particular engine/ carburetor, the stock carb has too large of a venturi. It doesn't draw fuel well, and needs help from muffler pressure. That in itself causes many problems, because now you have changing fuel pressure with rpm. There is no pressure at idle, so the low needle needs to be on the rich side. As soon as you open the throttle, there IS pressure, and now you are very rich. The high needle ONLY controls the mixture at full throttle, so it is not affected as much by the high muffler pressure. However, with the stock muffler, the pressure at full throttle is very high, so the needle needs to be made leaner than if it had less pressure. All this does is add up to a very non- linear carb. With the right size venturi, one that draws fuel well without help from the muffler, the tank pressure is more consistent and therefore the mixture stays more consistent. When I said I think the engine would like the 15% nitro better, that is because of the very slight hesitation when coming off of idle. Everybody knows that higher nitro idles and transitions better. I use the lowest nitro that works well. If it would run on 0, I would use it.
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Fly it till you break it!
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All Forums >> Glow Engines, Gas Engines, Fuel & Mfg Support Forums >> Glow Engines >> RE: My 2300 only likes one prop 
RE: My 2300 only likes one prop - 
at 2500ft. The guy answering him is in Corpus Christi at sea level telling him he should be getting 12,500rpms on a 13/8 prop. Who is right? Who is wrong? Were the original specs tested at sea level or not? Prove it? 