If Ok, rule #1...Never ever run a nitro car without a failsafe! EVER! This is one of the most basic rules u need to know. Now, when it comes to the needles, the high needle is used for tuning the top end of ur engine, ( half throttle to full throttle), this needs to be tuned first, ( in most cases, especially stock engines ) u want to lean it out till u hear the engine running strong, but still with a little smoke when running at full throttle, I prefer to lean mine out till it's at max power and sounds really good, then back it off a hair to leave it a little rich to lengthen engine life. Remember, the leaner u run it, the higher the temps, and the shorter ur engine life. Also, only turn the needle about an 1/8 turn at a time. Now, as far as the LOW NEEDLE is concerned, it the most tempermental of the two, it will control from take off to half throttle. U may notice some lag in the take off of ur car when the low needle is rich, u want to lean it out with very very small increments, like a 1/32 at a time or even less, lean it out till u have a good strong and smooth take off and smooth transition to full throttle. A good way to test the low needle is to pinch off the fuel line about a 1/2 inch from where it runs into the carb body. If it revs up for a second then shuts off, ur good. If it revs up and continues to rev, ur still rich, if it shuts right off, ur lean. If u still need help, just let us know, that's what we're here for.