Jet sizing
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Fleet Mechanic
Joined: Jan 2011
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From: West Valley City
Jet sizing
I'm thinking about changing the jet in my carb to a smaller jet so I get better mileage. What size would you guys recommend for high altitude? Also, do I need to change my metering rod at the same time? I have the stock feedback 1bbl carb on my truck. I bought the carb from guaranteed carburetors in Oct, so I'm sure its jetted for sea level. Thanks in advance guys.
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Joined: Nov 2007
Posts: 22,415
Likes: 92
From: Denver Metro Area, CO
Holley recommends going down one jet size for every 2,000 feet in elevation.
I have no idea where you're at (click on User CP in the top-left to change that, so we can
see where you're from) but I suggest looking at your current jet(s) and adjusting the size
from there.
I have never heard of changing the metering rod, but some people recommend also
changing the power valve.
This kind of tuning is greatly aided by an exhaust sniffer, but you'll also look at the spark
pugs after around 1,000 miles (install new ones now so you can discern a color difference in
the insulator surrounding the electrode later) as well as general operational characteristics of
the engine.
I have no idea where you're at (click on User CP in the top-left to change that, so we can
see where you're from) but I suggest looking at your current jet(s) and adjusting the size
from there.
I have never heard of changing the metering rod, but some people recommend also
changing the power valve.
This kind of tuning is greatly aided by an exhaust sniffer, but you'll also look at the spark
pugs after around 1,000 miles (install new ones now so you can discern a color difference in
the insulator surrounding the electrode later) as well as general operational characteristics of
the engine.
Moderator
Joined: Jan 2001
Posts: 56,993
Likes: 2,741
From: Virginia
If you have the feedback system with the computer, and it's all working, you should not need to change the jetting, it adjusts the mixture automatically.
Ford didn't add all those wires, sensors, and computer on the first feedback carb systems just to aggravate mechanics and owners when they try to work on them. All this tunes the mixture as you drive, with the oxygen sensor, and I believe it also has a barometric sensor that senses altitude changes.
Ford didn't add all those wires, sensors, and computer on the first feedback carb systems just to aggravate mechanics and owners when they try to work on them. All this tunes the mixture as you drive, with the oxygen sensor, and I believe it also has a barometric sensor that senses altitude changes.
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