Much needed low-end needle-valve adjustment

Radio Control Car Action, Dec 2002 by Gunderson, Nick

MUCH NEEDED LOW-END NEEDLE-VALVE ADJUSTMENT

I am having trouble with the brakes on my Duratrax Maximum ST. The truck stops when I apply the brakes, but the engine stalls if I keep the brake on for more than 1 second. I have a Hitec throttle/brake servo that appears to be working fine. I adjusted the idle stop screw to make the engine idle a little higher, but that didn't work, either. Do you have any advice for me?

Nick Gunderson

Ham Lake, MN

It doesn't sound as though your engine's low-end needle valve is adjusted property, Nick, so here's a simple way to do it. First, get yourengine up to running temperature by driving your truck around for a couple of minutes. Next, rev the engine to clear the excess fuel out of the carburetor and then pinch the fuel line approximately 3 inches from the fuel-line pickup. Listen to how the engine responds; ideally, it should start to rev up and then sputter after the fuel line has been pinched for approximately 3 to 4 seconds. If the engine starts to rev but sputters out immediately-within i or 2 seconds-the needle valve is set too lean. Richen the air/fuel mixture by turning the low-end needle valve counterclockwise about 1/8 turn. Conversely, if the engine does not respond for 5 seconds or more, the air/fuel mixture is set too rich. Lean it out by turning the low-speed needle valve clockwise 1/8 turn, and then repeat the test.

To achieve proper engine idle, you'll probably need to adjust the idle stop screw after you've adjusted the low-end needle valve. Turn the idle stop screw clockwise or counterclockwise as needed to provide a smooth and consistent idle. If you follow these tips, your engine should be able to idle for more than 30 seconds without stalling with the brakes applied.