Late Model YFA (aluminum base)
How To Adjust Metering Rod
The main metering rod adjustment is necessary on this design carburetor to ensure that the proper amount of fuel is allowed to enter the main well under various engine load conditions. The end of the metering rod that goes through the main jet is tapered or “stepped” … that is, the end is smaller than the next step, which is smaller than the step above it, etc …. By use of this design, we have in effect, a variable orifice for metering purposes. As the rod is lifted upward, more fuel is allowed to flow through the main jet. To make this adjustment, the air horn and gasket must be removed.
- Close throttle plate and press down on the diaphragm shaft until it bottoms in the vacuum chamber.
- Check the position of the metering rod.
- • It should be touching the bottom of the metering rod well.
- • The rod itself should contact the lifter link at the lifting lug and at the diaphragm shaft.
- • Bend the metering rod pin flange (on the metering rod arm) if necessary to properly position the metering rod,
- On current designed models, an adjusting screw is provided.
- • Turn screw until the rod just bottoms in the well . . . then, turn clockwise one additional turn to obtain the final setting.
- Install the air horn and attaching parts.
- It is good practice to always use a new air horn gasket when this adjustment is made.
