Tun­ing the Nee­dle Valves

RC Car Action - - HOW TO TUNE A NITRO ENGINE -

Ni­tro en­gines use nee­dle valves, or “nee­dles” for short, to con­trol how much fuel is in the fuel/air mix­ture. Some sport en­gines only have one nee­dle, but most have two: a “low-end” nee­dle that con­trols the fuel/ air mix­ture from idle to about half-throt­tle, and a “high-end” nee­dle that con­trols the mix­ture from about half-throt­tle to full throt­tle. The nee­dles are tuned by turn­ing them with a screw­driver. Turn­ing the nee­dle coun­ter­clock­wise will in­crease the amount of fuel in the mix­ture, or “richen” it. Turn­ing the nee­dle clock­wise re­duces the amount of fuel in the mix­ture, or “lean it out.”

When tun­ing the nee­dles, think of the hours on a clock face. Once your en­gine’s tune is close, you should only need to make ad­just­ments “one hour” at a time. Un­less your en­gine is way out of tune, ad­just­ments more than “three hours” (one quar­ter turn) should not be re­quired.

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