RC Model Reviews

Bummer about the JBAs, they have good prices. I suppose I will have to stick with my cheap Aviastars.

Yeah, I was disappointed - they "look" much like an OS-Ax engine but they sure don't run like one.

HI THERE EVERYONE a friend of mine was having problems with same IC engine and fixed it very easy...he opened the carby and took away the needle for high speed (full RPM) or also known as fuel flow needle
I am NOT talking about the little needle that is set with a screw driver
He put the needle on handheld bore machine (you can use LATHE if you have- it is the better option) and using a FILE he shaped the edge of the needle (i dont know how esactly because he had already assembeled the carby)
so after that he told me that he had a great mid range repsonse !
BUT BE CAREFUL- I suggest that you try few times shaping the edge of the needle GENTLY and try the engine EACH time to get OPTIMUM results without over "filing" the needle!
Also use the Bruce's advice-for the glow plug!!
GOOD LUCK EVERYONE!!

Actually -- you need to change the profile of the *low* speed needle (the one that you do adjust with a screwdriver) to alter the mid-range.

Changing the hi-speed needle will do nothing except alter the number of turns needed to get the right hi-speed mixture.

If you look down the throat of the carby while you move the throttle arm you'll see why that is.

Note that the carby barrel moves in and out as it opens and closes. As it moves in (when you close the throttle), the LOW SPEED needle starts to go into the hole on the end of the fuel-jet. This reduces the amount of fuel that can flow and thus controls the mid-range and idle mixture.

If you make your low-speed needle more sharply tapered then you will get a rich mid-range. If you give it a more shallow taper you will get a leaner mid-range.

Sometimes to get an engine "dead right" you end up having a slight curve to the profile of the needle so that the mixture remains ideal throughout the barrel rotation.

Generally speaking, if an engine's so bad that you have to modify the needle I don't bother using it. There are too many well-priced "good" engines to waste time redesigning a bad one

SORRY MY MISTAKE!!!!
I have mistaken the low RPM nad the HIGH RPM needle valve....
you have to shape the small needle valve!
SOrry for my mistake again and thanx to Bruce who quickly corrected my mistake!