Altitude Compensation Table Weber Jetting

Tech chat w/ Marc Matzer
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Marc
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Joined: Tue Mar 21, 2006 1:15 pm

Altitude Compensation Table Weber Jetting

Post by Marc » Tue Jan 15, 2008 10:47 am

Running your car at higher altitude will require you to re-jet your carb.The figure in this table represent several MAIN jet sizes and the appropriate altitude correction if the "normal" jet is correct anywhere between sea level and 5000'.
The correction is to compensate for the tendency of the fuel delivery system to go richer at high altitude as the amount oxygen diminishes.
This is for all Weber carbs regardless of model.Compare your jet # to the closest ,"leanest" jet on the chart ,if you dont see the same number here.

For example :Fiat 124 with twin 40idf's .Main jets are ok at 200 feet above sea level where you live or drive the car. Your main jets happen to be 150.You move to a new location which is 5280' above sea level and your car seems to be a bit sluggish.After checking everything in the car and knowing everything is in perfect working order,you check your spark plugs,and determine your Fiat is running rich .Checking the chart you would select a 145 main jet which is one step leaner to make up for a lack of oxygen in the combustion process above 5000'
0-5000' 5000'-6500' 6600'-9800' 9800-13000'
2.00 1.925 1.85 1.80
1.75 1.70 1.65 1.60
1.50 1.45 1.40 1.35
1.25 1.20 1.15 1.13
1.00 0.96 0.94 0.92

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