Manual - Great Hobbies

THE TRX 3.3 RACING ENGINEWater Valve(Controls Overall Flow)High Speed Needlepoint, fuel metering is entirely controlled by the high-speed needle.Again, using our water hose example, when the spray nozzle at theend of our garden hose is fully open, then the main water valve canbe used to adjust how fast the water flows.The engine’s performance is directly linked to the fuel mixture.Richening the fuel mixture increases the amount of fuel in theair/fuel mixture ratio and leaning the fuel mixture decreases theamount of fuel in the air/fuel mixture ratio.LeanWater Nozzle(Controls Fine Flow)Low Speed NeedleRichenRichSlightly lean fuel mixtures deliver stronger, more efficientcombustion and more power, but with less lubrication.Slightly rich fuel mixtures deliver cooler running and morelubrication but with slightly less power.Tuning the engine means finding the perfect balance between thetwo; excellent power to meet your needs while maintaining goodlubrication for long engine life. The optimal fuel mixture settingis rich to provide a safety margin against having a lean condition ifsome variable changes (such as the temperature from one day tothe next).General fuel mixture settings are measured by the number of turnsthe needles are turned out from fully closed. The fuel mixture settingshave been pre-set from the factory to typical break-in settings. Donot readjust your carburetor from the factory settings until after theengine is started and running, and you have been able to observe theengine running to assess what minor adjustments may be requiredto compensate for fuel, temperature, and altitude. Adjustments areusually made in 1/8 or 1/16-turn increments. If the engine sticks at topdead center (TDC), see page 36 for instructions on freeing the engine.The Idle Speed AdjustmentThe idle speed screw controls the closed position of the throttle slide.When the throttle servo is in its neutral position, the throttle slideshould be stopped against the idle adjustment screw. Always usethe idle speed adjusting screw to control engine idle. Do not use thethrottle trim on the transmitter to adjust idle speed. The idle speedshould be set as low as possible and still maintain reliable running.See Tuning Your TRX 3.3Racing Engine on page 26for complete information onadjusting the air/fuel mixtureand idle speed.Factory Needle SettingsIf your factory presetcarburetor adjustments havebeen tampered with, use thefollowing settings:• Set the high-speed needle to4 turns out from closed.• Set the low-speed needle sothe screw head (red in Fig. A)is flush (even) with the endof the slide (yellow in Fig. A).Fig. ALow SpeedNeedle AdjustmentAlways use the factorysettings for initial starting.Only use these settings whenthe factory settings havebeen lost.Higher nitro requires a richerfuel mixture. When running33% fuel, richen your highspeedneedle 3/4 turn ifpreviously running 20% nitroand then re-tune the enginefor maximum performance.JATO 3.3 • 21