Which way do you carb?
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Senior User
Joined: Feb 2005
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Which way do you carb?
I need some professional input on the topic of which direction one should mount a 4bbl carb.
I put a Holley 390 on my 300-I6 and have it mounted so the primaries are facing the front of the truck and the secondaries are toward the back. Should it be this way, or should it be turned 90 degrees so the primaries are away from the engine, and the secondaries are toward the engine?
There are a couple other threads where I've mentioned the way I mounted my carb, and it has been working very well for me in this position considering I don't have a dual plane manifold.
Does it matter? Is there some rule about it somewhere? Does anyone care?
Check the picks of my carb in my gallery.
Thanks!
I put a Holley 390 on my 300-I6 and have it mounted so the primaries are facing the front of the truck and the secondaries are toward the back. Should it be this way, or should it be turned 90 degrees so the primaries are away from the engine, and the secondaries are toward the engine?
There are a couple other threads where I've mentioned the way I mounted my carb, and it has been working very well for me in this position considering I don't have a dual plane manifold.
Does it matter? Is there some rule about it somewhere? Does anyone care?
Check the picks of my carb in my gallery.
Thanks!
Senior User
Joined: Feb 2006
Posts: 479
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From: Sonoma, CA
I don't know the answer. How do the plugs look. The only thought I have is that it may tend to draw a little more or less fuel to certain cylinders the way you have it mounted when primaries open vs. secondaries. Mounted 90 degrees from where it is may supply a more consistent fuel supply through the intake since the primaries and secondaries will be lined up paralell with the head. Then again, it may not make a bit of difference but you got me curious.
Posting Guru
Joined: Jul 2003
Posts: 2,232
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From: Colville, Washington
Dan, you have it mounted correctly. The bolt pattern on the Holley is not square, so it will not mount sideways, the holes won't line up. If you mount it 180* around, it will work, but the manifold was not designed to be used that way and I think you would have mixture problems.
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Thanks for the input Putt! 
Actually, the Holley 390 must be square, because I originally had it 90* out from where it is now. I had it so the primaries were facing away from the engine. Mostly in the interest of making the throttle cable connection without too much trouble, I turned the carb to where it is now (you can see it in my gallery).
So, it's been working this way for a year and a half, but does anyone know which way it should be?
Actually, the Holley 390 must be square, because I originally had it 90* out from where it is now. I had it so the primaries were facing away from the engine. Mostly in the interest of making the throttle cable connection without too much trouble, I turned the carb to where it is now (you can see it in my gallery).
So, it's been working this way for a year and a half, but does anyone know which way it should be?
Hotshot
Joined: Oct 2002
Posts: 18,488
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From: The Big, Oregon
If it's a single plane manifold, it will run more smoothly with the primaries facing out, but if it's a dual plane, you have it on the right way. I ran an Offenhauser C series single plane intake for two years, with a Motorcraft 2150 on it mounted the way your Holley is, it ran ok, but I always wanted to turn it sideways for a more even mix.
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