Questions on choosing the right Carb

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Motorboy
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Questions on choosing the right Carb

Post #1 by Motorboy » Sun Jan 07, 2018 11:24 am

Hi All! Newbie here, looking for some knowledge on how to pick the right carburetor for my setup. I apologize in advance for the long post. I suck at brevity.

I just joined, but I’ve been scouring the treads looking for some insight. So far what I have found are a lot of different perspectives and opinions, but that just leaves me with more questions than answers. Unfortunately many of the more informative threads haven’t been commented on in several years.

My project: 1980 F-250 300 six, np435, np208, Dana 60 rear, ttb Dana 44 front w/410 gears. This was a PA farm truck for the past 30 years so who knows how many times the odo flipped. But it reads x06,534. The drive train shows a lot of wear, but when I’ve changed the oil, I saw no metal in the coffee filter. The compression read between 144-147 psi on all cylinders, and not too much sludge in the valve-train. So I think I have a relatively healthy block.

What I want: Reliability, crisp throttle, and torque. Also, a carb under $350 if possible.
What I have: (Not installed yet: Offy C Series intake, HEI Distributor, efi manifolds) Stock block with a 3’’ cat 3’’ muffler to a stove pipe. (Kind of silly but it’s fun, came with the truck, and sounds good)

What I want to know: Advantages/Disadvantages of a 2v vs 4v carb setup. How big do I need?
I see some people claiming great street-ability with big ( 4v 500+ cfm) carbs, others claim many over carb their engines. I know 2v and 4v carbs are measured differently, and port velocity and setup can change how a carb works.

So far I like the Holley 2300 500 cfm. It’s at my price point and I can easily buy parts for it. Thoughts?

wallen7
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Re: Questions on choosing the right Carb

Post #2 by wallen7 » Sun Jan 07, 2018 3:37 pm

Sounds like a good plan. You can easily change carbs later if you don't like that one. If I was going to use a 2bbl I would get a good adapter plate like a Moroso or maybe one of the other manufacturers. Stay away for the cheapies as they don't fit well and can cause vacuum leaks.

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THE FRENCHTOWN FLYER
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Re: Questions on choosing the right Carb

Post #3 by THE FRENCHTOWN FLYER » Mon Jan 08, 2018 7:05 pm

Motorboy wrote:What I want: Reliability, crisp throttle, and torque. Also, a carb under $350 if possible.

If the older threads pointed you in the direction of an Autolite 1.08 2-barrel then they are still relevant. The Autolite/Motorcraft offers many advantages over the much touted Holley 500 and at a lesser price. My personal experience with a 500 Holley on the street was less than spectacular.
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Motorboy
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Re: Questions on choosing the right Carb

Post #4 by Motorboy » Fri Jan 12, 2018 11:36 am

Thanks for the input. I know a lot of people love the Autolite 2100. My only hesitation is they are no longer made and i would most likely have to buy an old one and rebuild it. I just don't have any experience with carburated vehicles other and motorcycles. I've rebuilt dozens of side draft carbs for Honda bikes, so I think i can manage.

Are there any good outfits that will sell a rebuilt one? I see a lot of stuff on ebay, but I trust my abilities over their reputations.

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Re: Questions on choosing the right Carb

Post #5 by wallen7 » Fri Jan 12, 2018 12:39 pm

Go ahead and find you a good core. What you would most probably want is one from a 302 or 289. This should be a 108 identified by the number cast on the main body near the throttle lever. They are easy to rebuild, pretty much straight foward.

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Re: Questions on choosing the right Carb

Post #6 by Lazy JW » Fri Jan 12, 2018 3:15 pm

Most everyone disagrees with me on this, but if I'm going to run a carburetor it needs to only have one barrel :mrgreen: Anything more complex might as well run EFI.
"The White OX" 1974 F-350 300-6, Stock single exhaust, Carter YF, T-18A, Dana70 w/4.11, Flatbed dually w/dump bed. "Where no oxen are, the crib is clean, but much increase is by the strength of the ox" (Proverbs 14:4)
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wallen7
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Re: Questions on choosing the right Carb

Post #7 by wallen7 » Fri Jan 12, 2018 5:04 pm

Go back to what the FTF has said in the past - put that 1BBL on a 302 and see what you think - The 2BBL Autolite or Motorcraft even if it is on an adapter to a 1BBL manifold will be an improvement.

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Re: Questions on choosing the right Carb

Post #8 by wallen7 » Fri Jan 12, 2018 5:06 pm

If you choose to go fuel injection you can't stay in your $350 budget.

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Re: Questions on choosing the right Carb

Post #9 by SteveP » Fri Jan 12, 2018 6:00 pm

I'm running a 300 (reman from S&J) with an Offy C intake, Hedmann dual exhaust header - no cats, 2" pipes with Flowmaster mufflers, Elgin 1178P cam, ported and polished head with 3 angle valve grind in front of a C6 trans (soon to be swapped for a AOD) and 3.08 rear axle.
When I was deciding what carb to run I read threads here on carb sizing and I was skeptical of recommendations for 4 bbls in the 500 - 700 cfm range as too big a carb can be as bad as too small for a street engine and a 300 isn't capable of flowing 500 cfm without extensive mods. I assume the big 4 bbls are for racing applications.
I referred to several carb sizing calculators online and they all calculated a flow of 332cfm @ 4500 rpm with 0.85 VE. I bought a MC 2150 with 1.21 venturis (351 cfm) from National Carburetors.com ($179.95 + core charge and shipping) and mounted it with a TransDapt 2065 adapter from Jegs. I wanted to make sure I had enough without overdoing it.
It turns out that this is more carb than I need as I never turn the engine any higher than 2600 rpm (194 cfm) (I cruise at 2450 rpm @ 70mph). The 1.08 venturis (287 cfm) would have been plenty for my application.
Even though I'm slightly over carbed the engine runs great and I'm happy with my choice.

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Re: Questions on choosing the right Carb

Post #10 by Motorboy » Fri Jan 12, 2018 8:56 pm

Lazy JW wrote:Most everyone disagrees with me on this, but if I'm going to run a carburetor it needs to only have one barrel :mrgreen: Anything more complex might as well run EFI.

I actually was pleased with the little YFA on the truck, but it suddenly developed a bad vac leak. Turns out the intake manifold had at one time been cracked, and poorly brazed back together. It redeveloped a crack, and gave me an excuse to hop up the old farm truck.

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Motorboy
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Re: Questions on choosing the right Carb

Post #11 by Motorboy » Fri Jan 12, 2018 10:05 pm

SteveP wrote:When I was deciding what carb to run I read threads here on carb sizing and I was skeptical of recommendations for 4 bbls in the 500 - 700 cfm range as too big a carb can be as bad as too small for a street engine and a 300 isn't capable of flowing 500 cfm without extensive mods. I assume the big 4 bbls are for racing applications.
I referred to several carb sizing calculators online and they all calculated a flow of 332cfm @ 4500 rpm with 0.85 VE. I bought a MC 2150 with 1.21 venturis (351 cfm) from National Carburetors.com ($179.95 + core charge and shipping) and mounted it with a TransDapt 2065 adapter from Jegs. I wanted to make sure I had enough without overdoing it.
It turns out that this is more carb than I need as I never turn the engine any higher than 2600 rpm (194 cfm) (I cruise at 2450 rpm @ 70mph). The 1.08 venturis (287 cfm) would have been plenty for my application.
Even though I'm slightly over carbed the engine runs great and I'm happy with my choice.


My original plan was to run a Holley 2300 350cfm, but several people talked me out of it; claiming it was way too small. After watching some videos on rebuilding the Autolite 2100, I think I'll be hunting for one. Did they make one with a manual choke? The whole point of this vehicle is to go as analog a possible. So far I've only seen ones with electric chokes.

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Re: Questions on choosing the right Carb

Post #12 by SteveP » Sat Jan 13, 2018 3:03 pm

My original plan was to run a Holley 2300 350cfm, but several people talked me out of it; claiming it was way too small. After watching some videos on rebuilding the Autolite 2100, I think I'll be hunting for one. Did they make one with a manual choke? The whole point of this vehicle is to go as analog a possible. So far I've only seen ones with electric chokes.

National has a 2100 with hand choke listed. When I bought mine I called and told them what I wanted and they fixed me right up.

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Re: Questions on choosing the right Carb

Post #13 by Motorboy » Mon Jan 15, 2018 3:41 pm

Thanks for all the advice Folks! I'll be giving National carburetor a call.

Side note: My mechanic happened to have an old 500 cfm holley 2300 lying around. When i saw how big the throttles were I thought "yup wayyy to big."

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