In some cases in high altitudes it may be necessary to use leaner metered main jets. Usually a 5% or 10% leaner jet will compensate for any variation in altitude. The metering jets are marked in thousandths of an inch of hole diameter; thus, the small the hole, the smaller the number on the jet.

The main jets can be removed and installed without disassembling or removing the carburetor from the engine in the following manner:

1. Remove the two main jet plugs and gaskets from the carburetor main body. Removal of these plugs will drain the fuel bowl.
2. Remove the main jets using a screwdriver having a screw starter blade.

NOTE: If the jet fails to stick to the end of the removing tool, but falls off into the fuel bowl, it may be necessary to remove the air horn assembly.

1. Install the main jets in the reverse of the removal operation. No gaskets are used with the main jets.

NOTE: Do not try to change the size of the power valve restriction (21), or the pump discharge nozzles (26), as this will cause erratic performance.