Merc manifold bore spacing and size

Kilohertz

Kilohertz

Senior Member
Hi guys,

In my pursuit of either fuel injection or a 2GC in the interim, I have located a Merc manifold but it is 10 hours away and the fellow is not technical and doesn't have computer or camera so I am wondering if you might be able to help me?

I need to know what the center-center bore spacing is on the Merc manifold. I believe the bore is 1 3/8"?? Also, is the 2GC bore spacing the same or are the bores slightly offset in one direction or another?

I have a complete fuel injection system on an old truck my neighbor gave me, but I don't want to strip in until I am positive I am going this direction as it still runs and drives. The small 2.8L S-10 engines have a throttle body with 1 3/8" bore, just not sure what the c-c spacing is. Going to try to find one of those today.

Thanks for your help.

Cheers
 
I don't have the measurements, but I can tell you the the 2G throttle bores (1 7/16") are not concentric with the Merc throttle bores (1 3/8"). When I bored my first couple of manifolds, I used a spare 2G carb base bolted to the manifold as a guide for the Rota-Broach I used to bore it. It worked perfectly and ensures that the bore job is at the proper angle as well as position.

Later, when small base 2G's became scarce, I used the base on a rebuilt carb. I replaced it with a chunk of 1 1/2" aluminum plate with the proper mounting holes and throttle bore holes (done with the 2G base before I "re-purposed" it).
 
Thanks Denny,

I knew you would know :) ....I am going to find a 2.8L TBI unit today which are supposed to be 1 3/8" bores, not sure what the spacing is but hopefully usable on the Merc manifold. I also found a 2GC but it's in the same town as the manifold, 10 hours away...Trying to find someone to pick them up for me.

Lots of other things to work on in the meantime.

Thanks again for the help.

Cheers
 
Maybe you can find a carburetor base gasket for a Merc 4-bolt; then you would have something to check against.

Also, make sure the 2G is a "small base" model. The newer ones have a bolt pattern that is just large enough not to be a close fit but large enough to prevent using a simple flat adapter.
 
tubman said:
Also, make sure the 2G is a "small base" model. The newer ones have a bolt pattern that is just large enough not to be a close fit but large enough to prevent using a simple flat adapter.
Click to expand...


The carb I found is still on a '65 chevy manifold, bolt spacing I think is 3.25" side to side. I think that is the small one.


cheers
 
I think that is the right carb. I found this on the internet :

The original “early” size has center to center stud dimensions of
2” x 3-¼” and a bore size of 1-7/16”. The larger base stud dimensions are
2” x 3-¾” with a bore size of 1-11/16”

It also has the cfm rating of a small base 2G. Note that it is just about double that of a 94.

Model 2G: 1-1/4-in. flange, 1-7/16-in. throttle bore, 1-3/32-in. venturi 278 cfm
 
.

The "2G" series was still being used in '65 on Chevys, although they may be of the "2GC" or even "2GV" type. "2GC" has the round choke housing attached, whereas the "2GV" has the choke stove mounted on the right side of the intake manifold. A plain ol' "2G" has a manual choke. DD


OIP.lJUXmSy8JMH4sObOiFvr5wHaE8
 
Hi Guys,

Finally getting back to my '49 Ford and have found a bevvy of Rochester 2 bbl carbs...A 2 hour drive to go see them..can anyone tell from this picture if they are the small base that I need? He won't be able to get to them to measure until the weekend.

Cheers
 

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Kilohertz said:
Hi Guys,

Finally getting back to my '49 Ford and have found a bevvy of Rochester 2 bbl carbs...A 2 hour drive to go see them..can anyone tell from this picture if they are the small base that I need? He won't be able to get to them to measure until the weekend.

Cheers
Click to expand...

Why don't you have him turn them over and take another couple pics???
 
.

Obviously, there were TWO different sizes of the BORES in baseplates between the "Small" 2Gs, and the "Big" 2Gs. The base bores in the little ones was 1-1/4" diameter. The base bores in the big 2Gs was 1-1/2". DD

Going by a chart that I cannot reproduce:

SMALL 2Gs all had 1-3/32" venturis = 278 CFM.

The BIG 2Gs had four different venturi sizes, w/four different CFM ratings.
1-3/16" venturi = 352 CFM

1-1/4" venturi = 381 CFM

1-5/16" venturi = 423 CFM

1-3/8" venturi = 435 CFM


.
 
Notice that all of those carburetors have the fuel inlet on the front, not the side. That means they are most likely "B-O-P" carburetors, as the desirable Chevrolet carburetors have the fuel inlets on the side. As I said yesterday, the Small Base Carb is ID'd by the air cleaner flange diameter of 2 5/8", while the Large Base Carb is ID'd by the air cleaner flange diameter of 3" or 3 1/16".

If I had to guess, I'd bet that those are large base carbs. Finding that many small-base "B-O-P" carbs would be pretty hard to do.
 
I’m really interested in this thread. I have a couple Merc manifolds and 2GC carbs. But, you lost me with “B-O-P”. What does that mean?….Thanks, Mark.
 
Okay thanks everyone, appreciate the help. Like I mentioned above, he won't have access to them until tomorrow to measure for me, I was just hoping the picture might be worth 1,000 words. :-)

Here's hoping...

Cheers
 
big job said:
You may also check out a straight eight Buick AA26 I think its a Stromburg
Click to expand...

I actually have a Stromberg WW which is the correct base. I'm going to have a close look at it this morning to see if it's complete, it's one of my core carbs I've had for years,

Cheers
 
Well my Stromberg WW is a core at best, crack in the base, and the 7 carbs mentioned above were all large base....but good news!! I found another group of 8 Rochester 2Gs and at least 3 are confirmed small base. My Dad picked them up today and will be coming for a visit this weekend.

Pics attached for confirmation.

cheers

my eye says middle top row and 1 and 2 from left on middle row.
 

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