testing 2x4 carbs

[studiog]

1961 270HP 2x4
I just rebuilt 2 four barrel Carter carbs for my rebuilt motor. I am having some problems with one of them. I think it is just one. Can I block off one carb at the intake and just run on the other so I can isolate the problem? I am running the stock manifold which I am sure is a single plane manifold. Anyone ever done this? Any input about these carbs also appreciated. Thanks for any replies.

 

[Boogieman]

I would tend to think that either the front or rear cylinders might be a little on the lean side with only one functional carb. I don't think I'd try that on mine. Good luck.

 

[studiog]

Thanks Boogieman, I would just do this as a test till I could dial in each carb separetely and make sure each is functioning properly. The front carb only kicks in under heavy acceleration as the linkage is progressive from the factory. I think you just helped me answer my own question. :L Any other input appreciated.

 

[magicv8]

Normally only one carb has idle jets - the other is for more power. If you disconnect the linkage to one carb, the other will be the only one in use. You may want to unscrew the idle stop a turn or two on the disconnected carb, to allow the throttle body to seal the manifold.

I have a friend who is looking for a rear carb of the 2x4 WCFB setup - who tells me it has no idle jets. If you know of one - I'd like to hear about it

 

[Tom Bryant]

Yes you can do that. As you know the car runs and drives most of the time on the primary side (front) of the rear carb. Only the rear carb has a choke. The secondary side of the rear carb and the entire front carb open at wide open throttle due to the design of the progressive linkage.

Both carbs have idle circuits and this leads to somewhat of a hard time getting a decent idle if you set them up according to the manual. You can follow magicv8's recommendation and back off the idle screw on one carb til the throttle blades are completely closed. Then gently seat the idle screws and you have shut off that carb. Now you can play with the other one to see what your problem is. Since both carbs have idle circuits you can do this to the front then reset it and do the same thing to the rear to check the front carb. With the engine warmed up it should run equally well on either carb by itself. The engine needs to be warm to do this since the front carb has no choke system.

Here is somthing I have done to make the engine run smoother. I'm not sure it really effects wide open throttle any since you are just closing the idle circuit. I've never done back to back timed runs to see if there is any difference either. Seem to accelerate just fine. I seat down the idle screws on the front carb and make all of my idle adjustments on the rear carb. Drives like a single 4 bbl til you stomp it. I don't see anything wrong with this meathod as the later 2x4 setups on the 409s didn't have an idle circuit in the front carb. It was just for stomp.

Here is a pictue of a 1961 set I have on the shelf. Easier to photograph than the ones on the car. I also have a spare pair of parts carbs blown apart in a box if you need any interior pics.

 

[Tom Bryant]

Please ignore the homemade fuel lines in the previous picture.That's the way that engine came out of a 1955 Corvette. (Complete 1961 270 horse) This picture is of the front carb. Note the hex shaped idle mixture adjustment screws unique to Corvettes and the absence of any provision for choke parts.

 

[Tom Bryant]

Here's one of the rear carb idles mixture screws. These carbs are all correct by the numbers and don't appear to have ever been off of the manifold. I aquired this engine in 1975 and it had set for several years before that.

Tom

 

[JohnZ]

It's a dual-plane manifold - pretty neat piece of foundry work with all that pattern/core complexity. The only reason the front (secondary) carb has an idle system is so it continues to be supplied with fresh fuel so the carb doesn't get gummed up when the car doesn't get stomped on often enough.

 

[Boogieman]

Well, maybe I stand corrected. I thought you might be trying to drive with only the one carb. My 2x4 experience was with older Mopar Max-Wedge cross ram intakes. Had one on my old race car and another on a street version. You DO NOT want to run with only one carb in that scenario. Burns pistons really quickly. Not much progression in that linkage. Have to tune them like 2-4 cylinder engines connected at the crank. Come to think of it, my 6-Pack runs off the center carb at idle and cruising.

 

[studiog]

Thanks everyone for all for the info. Thanks Tom for the Pics very helpful. OK JohnZ dual plane but not dual plane front to rear just side to side???

 

[JohnZ]

Front-to-rear for all eight; the rear carb feeds all eight cylinders (normal operation), and so does the front carb (when the progressive linkage opens it); like I said, it's a pretty neat piece of foundry work, especially for its time - it was designed in 1955 (for 1956), and was used through 1961.