Carburetor Schoolage

BallzF250

Well-Known Member
Joined
Feb 24, 2010
Location
Wilmington
So...I know nothing really about carburetors. I'm about to acquire a truck with a Ford big block 400 in it. I believe it has the stock carburetor (I think that's a 2 barrel). I've been told that it either needs to be cleaned and rebuilt or just flatout replaced. I think I'd like to go with the replace option. Out of the little bit of research I've done...I know I'd like to put a 600 or 650 cfm on it...and I'd like it to be a 4-barrel.

So my question...are carburetors universal fit? Like if I find someone on Craigslist or something advertising a holley 650 carb that just needs to be rebuilt (hypothetical...haven't actually looked)...would I be able to get it, rebuild it, and just slap it on the engine and have it work?

School me oh great ones!
 
I don't know a whole lot on the different sizes and bolt patterns but I do know if you are going from a 2brl to a 4brl you will need a new intake designed for a 4brl I would suggest going with a holley or better yet a demon carb they are the same bolt pattern so either would be a good choice, both are easy to tune but the demons have some improvements over the holley that I like especially tuning my 440
 
You'll have to get a 4 barrel intake for your motor. 4bbl carbs are available in squarebore and spreadbore. Squarebore carbs have primaries and secondaries that are about the same size. Spreadbore carbs have smaller primaries and larger secondaries (Rochester Quadrajets are most common, but other aftermarket spreadbores are available). Spreadbore carbs are suppose to be more fuel efficient under normal driving conditions, but with a 400 Ford, don't expect gas mileage to be a priority.

A typical Holley 4bbl uses a larger bolt pattern than Edelbrock's and Carter AFB's, but most aftermarket intakes will have bolt holes for either.

You can get carbs with manual or vaccuum secondaries. With manual secondaries (Holley double pumpers is an example) the linkage begins to open the secondaries around half throttle regardless of load on the engine. Vaccuum secondary carbs (Holley 1850's or 3310's) open the secondaries based on throttle position and load.

Manual or electric chokes are available on most aftermarket carbs.

You did not say if you have an auto tranny, but if you do, you will need a carb with the trans kick down linkage for the Ford.
 
It's got a 4spd manual trans. So basically I need to get a new intake if I upgrade to a 4barrel.

I know it has a new manual choke as well. Is this the sort of manual like I'd have to adjust from the cab or manual like its mechanically done by some linkage to something else? Havent seen then truck yet so I'll probably get better understandings once I can put eyes on parts.
 
If this is going to be an off road rig for places like URE, choose the 4bbl carb carefully......the two barrel motorcraft carb will do better than most holleys in hill climb & off camber situations.

Good luck!
 
A manual choke will normally have a push/pull cable mounted in the cab. If you replace the carb, you can more than likely use the choke cable with a different manual choke 4bbl.
 
IMO stay with the Motorcraft 2brl. It will be cheaper to work on and maintain. The 400M engines don't like high RPM either. If you really want to go 4brl get a quadrajet from a late 70s GM with electric choke and a dual plane intake spread bore design.
 
I'd convert it to TBI using junk yards parts.
 
I'd go with an edelbrock carb over a Holley, much easier to work with and not hormonal during weather changes.
 
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