2009 INOA Rally

July 20-24, 2009

High Altitude Carb Jetting

The rally site is 7800 feet above sealevel. You can expect to be riding at elevations between 7,000 and 11,000 feet during the rally. There are two main consequences of high elevation for the performance of your Norton (and any other normally-aspirated, non-fuel-injected, internal combustion engine):

The air-fuel mixture will become richer at high elevations.
Even if you rejet to get the correct air-fuel ratio, the engine will produce less power. The rule of thumb is about 3% power loss for every 1000 feet of elevation increase.

For those of you who are coming to the rally from lower elevations, we offer the following advice on jetting for stock 750 and 850 Commandos at these elevations. No single set of jets will work optimally over the full range of elevations in Colorado, but these will keep you running reasonable well. The single most important setting on a Commando is probably the needle position. If you do nothing else, plan to drop the needles one notch from their normal position, unless you normally ride at 5000 feet or above.

Amals

200 main jets
needle in middle position
105 needle jet

Mikunis

3.0 slide
159 po needle jet
6DH3 needle with clip in the middle
230 main jet
35 pilot jet

Return to the main Rally Web Page


	2009 INOA Rally July 20-24, 2009 High Altitude Carb Jetting The rally site is 7800 feet above sealevel. You can expect to be riding at elevations between 7,000 and 11,000 feet during the rally. There are two main consequences of high elevation for the performance of your Norton (and any other normally-aspirated, non-fuel-injected, internal combustion engine): The air-fuel mixture will become richer at high elevations. Even if you rejet to get the correct air-fuel ratio, the engine will produce less power. The rule of thumb is about 3% power loss for every 1000 feet of elevation increase. For those of you who are coming to the rally from lower elevations, we offer the following advice on jetting for stock 750 and 850 Commandos at these elevations. No single set of jets will work optimally over the full range of elevations in Colorado, but these will keep you running reasonable well. The single most important setting on a Commando is probably the needle position. If you do nothing else, plan to drop the needles one notch from their normal position, unless you normally ride at 5000 feet or above. Amals 200 main jets needle in middle position 105 needle jet Mikunis 3.0 slide 159 po needle jet 6DH3 needle with clip in the middle 230 main jet 35 pilot jet Return to the main Rally Web Page