How much nitro are ya'll using in your .049's &.061's?

With the venturi necked down and using an exhaust throttle and of course adding 2 or 3 shims under the glowhead you can fly with nitro contents as low as 5%.
Normally 15% and up is preferred by these small engines.
Alot depends on temperature and humidity also.

I've seen guys use 10% but I like 25 better.........

I use 40% in my tee dees, with a texaco 7 fin head and 3 gskts, under it also use a pressure system, and fuel line on the needle, with this combo the motor lites right off and the needle sensitivity is non exsistant, and my planes really haul,

I've been using Byron's 25% "1/2A" fuel with 1 to 2 oz. extra castor oil per quart in my Cox engines. Messy? Yup, but engine life (piston/rod ball/socket) is good! I think I've heard Norvel users say they use 25% nitro with some synthetic oil with good success. The castor is a MUST for Cox engines, IMO.

As mentioned above by several, lower compression when using throttle sleeves helps the Cox engines a lot. I use either standard Babe Bee or Texaco heads with extra gaskets, depending on the prop loading. 6x3's, 6X4's or 7x3.5's need less compression by far than a 5x3.

Milton

Seems it's zero to around 60%, depending on what you want to do. The nitro increases power by supplying its own oxygen and by cooling the mixture.

I've been mixing my own of late, tried 25-25-50 (NOM) then 20-20-60 and 30-20-50, I felt that 20-20 ran better than the 25-25, and the 30-20 only produced about an extra 300-400 RPM on various size props, so I'll think I'll settle for 20-20-60 as the nitro is quite expensive and the extra RPMs are not too significant.

I use Sig 1/2A fuel...25% nitro and 18% oil (1/2 synth and 1/2 castor)

If it's a Cox Surestart then I use 25 % with 20% oil. They don't have the best piston to cylinder fit.

Sig 1/2A fuel here as well.

I use the Sig Champion 25% as well but add two ounces per quart of extra castor oil.

In the past I've used ACE, and Byrons 25%. I don't think these are availible anymore. I go for SIG champion 25% and add 1-1 1/2 ozs. of caster. If I feeling wicked I use some 35% champion with added caster. If I can't use SIG I'll use some 25% generic and add caster. But at least 25% nitro.

regards - Steve B.

My brother says he and his friends used to run 90% nitromethane in Cox 049 reedies for short car drag races. The engines didn't survive many runs, and they were hard to start, even for professional racing mechanics with lots of power tools.