Changing main jets
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Senior User
Joined: Jul 2003
Posts: 165
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From: St. Louis, MO
Changing main jets
What do I tell the counter dumby at the local auto parts store that I am looking for main jets for my Motorcraft 2150? Is there a specific part number or name I need to use?
Will Holley jets fit the Motorcraft?
Thanks.
Will Holley jets fit the Motorcraft?
Thanks.
Tuned
Joined: Jul 2003
Posts: 455
Likes: 3
From: Berkeley
holley jets are NOT the same as the motorcraft ones.
i got jets here: http://www.carbsunlimited.com/ford2v.htm
btw: my mildly built 400 currently runs kinda lean on #60 jets.
thinking of trying 63's. what are you running/going to?
cheers!
i got jets here: http://www.carbsunlimited.com/ford2v.htm
btw: my mildly built 400 currently runs kinda lean on #60 jets.
thinking of trying 63's. what are you running/going to?
cheers!
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Senior User
Joined: Jul 2003
Posts: 165
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From: St. Louis, MO
Well, I'm not sure what I am running...yet. I just know that changing the jet sizes were my next step for my rebuild.
I'm running a 351M. Hopefully, by next fall I'll stroke it to 400. But before then, I just wanted to tune it as much as possible.
Thanks.
I'm running a 351M. Hopefully, by next fall I'll stroke it to 400. But before then, I just wanted to tune it as much as possible.
Thanks.
Posting Guru
Joined: Aug 2000
Posts: 1,984
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Redone, I'd guess that you're running #57's, if it's a factory carb. That's what was in my 78 Bronco. I switched mine to 60's to cure pinging, and now it's slightly on the rich side according to the plug color. I'm thinking of going back down a size or two. It seems that a little jet size change will go a long way, at least on my (stock) 351M.
Posting Guru
Joined: Aug 2000
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From: (near) Denver USA
The effect of changing jet sizes depends on your altitude and on the sizes you are changing. Other factors being equal, changing from 60 to 62 will have more effect on A/F ratio than changing from 50 to 52. And changing from 60 to 62 at 200 feet above sea level will have less effect on A/F ratio than changing from 60 to 62 at 5000 feet above sea level.
The optimum jet size depends a lot on altitude. The size that works best on your engine at 5000 feet above sea level is not the same size that works best on your engine at 200 feet above sea level.
The optimum jet size also depends on volumetric efficiency, which varies with the components (especially the camshaft), and even over time as an engine wears out. So the size that works best on your engine at 5000 feet above sea level might not be the same size that works best on my engine at 5000 feet above sea level.
Unless you have access to an exhaust gas analyzer (measures CO, CO2, and HC at least), tuning the carb jet size is a lengthy trial-and-error process. You just have to keep making incremental changes and measuring the results until you zero in on the right size.
The optimum jet size depends a lot on altitude. The size that works best on your engine at 5000 feet above sea level is not the same size that works best on your engine at 200 feet above sea level.
The optimum jet size also depends on volumetric efficiency, which varies with the components (especially the camshaft), and even over time as an engine wears out. So the size that works best on your engine at 5000 feet above sea level might not be the same size that works best on my engine at 5000 feet above sea level.
Unless you have access to an exhaust gas analyzer (measures CO, CO2, and HC at least), tuning the carb jet size is a lengthy trial-and-error process. You just have to keep making incremental changes and measuring the results until you zero in on the right size.
Senior User
Joined: Oct 2003
Posts: 347
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From: in a house
it would aslo be a good idea to smooth out the air horn casting marks to improve flow. each carb will vary but it takes less than an hour with the right tools and know how. a very fine grit wheel in a dremel works well.
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