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I have dual Carter WCFB carburettors in my '58, and have a question about setting up the linkage between the two. I have checked the servicing guide, AIM and a few catalogs and nothing seems to give me a precise answer.
When I received the car the front carburettor only kicked in at about 1500rpm when the rod head engaged the clevis. The clevis was connected to the lower right hole on the throttle lever, so the rod angled down and the rod head extended 3/4" to 1" from the clevis. This meant the front four cylinders would run very lean and may have been done to improve fuel economy?
I adjusted the linkage for the front to move the clevis to the upper left hole on the front carby which reduced the rod head extension to about 0.4". See photos.
In this setup with the accelerator flat to the floor and the throttle fully open on the back carby, there is still unused throttle on the front carby - about 0.5" of rotation.
My question is - should I adjust the front carburettor rod so there is no clearance from the clevis so bath carbs operate at the same time, or leave some gap (and if so, how much?) such that the front carb operates on a progressive basis?
Your front carburetor is not the correct one for the application. I'm not sure about the rear.
The throttle levers on both appear wrong to me. That horizontal bend in the lever on your front carb is for some other application. I have no idea what type carb it is, but it also has a "thick" base, which is the type used on singe-four carb engines. It may be a '56 carb as it has the adjustment screw on the side of the base.
But IIRC, even with all correct hardware, I have seen that there is always some throttle left in the front carb at full accelerator pedal.
This is what it should have for levers, etc. In the 1st photo the background carb is the secondary, foreground is the primary.
secondary carb = Front -----------primary carb - Rear
With the proper carbs with correct levers, the linkage is progressive such that.....
Half throttle on the primary carb then starts to engage the secondary carb "primaries". The secondary carb is still inactive.
Past half throttle, the accelerator lever continues to open the "secondaries" on the primary carb, and the "primaries" of the secondary carb begin to open.
At apx 3/4 throttle, the "secondaries" of the secondary carb begin to open.
At full throttle, all secondaries will be fully open.
Rich is correct in every regard - you seem to want to hook your carbs up "shotgun" (both coming on evenly) vs "progressive" (the front carb coming on when the throttle is at some point in opening). Almost nobody runs shotgun unless racing; progressive is the way to go. Yes, the fuel distribution at low speeds is a little funky but it evens out as you drive. Hook them up progressively and they'll be fine. I've run mine like that for 9 years.
As stated, due to the geometry involved, you may leave a VERY small amount of front throttle on the table at WOT but its hardly noticeable. You have about 768 cfm all told and the rear flappers will supply the engine what it asks for...there is always some reserve...
Set the carbs up so the front "comes on" at 1/2 throttle and it'll work nicely.
If the number on the front carb air horn is 6-1310 (its hard to see) it may be a '56-'58 Chrysler dual quad carb...
Last edited by Frankie the Fink; 02-12-2015 at 06:32 AM.
The carbs are not original to the car - from searching the web I believe they may be originally Chrysler carbs. The air horn castings are both numbered 6-1310 with the front stamped 1306 and the rear stamped 1307, and the main body castings are 0-1158. These are not Corvette numbers.
Your comments on the progressive nature of the carbs are valuable. I was worried that the front cylinders would not get their share of fuel, but obviously the vacuum adequately delivers the fuel from the back primary carb to the front. I had two gummed up cold spark plugs in the front two cylinders causing misfires but this must have been coincidence.
That would make them Chrysler 2x4 carbs for sure; air-horn and body numbers are for '56-'58 but you may have a mis-matched base in the front...they are good carbs.
You could try running NGK-XR4 plugs in the motor - that is what I run; they burn nicely and reduce fouling...
You can read more about your Chrysler carbs on the first page of this article.
Last edited by Frankie the Fink; 02-12-2015 at 06:58 AM.
David, Also, ust to clarify your thought about a "lean" condition on the forward 4 cylinders......
The 3739653 intake manifold is internally ported such that either carb will eventually feed all 8 cylinders. At idle, with the progressive linkage, you can activate the front carb throttle and still get proper fuel flow.
Up to half throttle, the rear(primary) carb will distribute the fuel/air mixture to all cylinders properly. It just takes a little longer, due to the further distance to get to the forward cylinders, but once flow has progressed all intake ports have adequate mixture.
I never really thought of it until now, but....... You basically have a "spare" carb up front. If your rear(primary) carb ever had a problem and becomes inoperational, say a blocked needle/seat or similar, on the road you could actually rework the linkage so that only the front carb is active. The engine wouldn't care where it's getting the mixture from, rear or front.
Even though your carbs may not be "Corvette" specific with the proper levers etc, it appears you could make them equivalent with the proper linkage adjustments. I see you're far away from our local Corvette suppliers.
You definitely don't want "full time" linkage on both. My '59 was setup that way when I first bought it nearly 29 years ago, and it ran way too rich and poor economy. Back then I made my own progressive dual linkage. Why? I couldn't/wouldn't spend the money on a $80+ repro linkage setup....... My 3 pre-teenage boys needed new sneakers that month for basketball season.
I replaced the set of NGK XR5 (one heat rating less than XR4) in there with NGK BP5S, as it was the equivalent of AC Delco R43S shown in the Zip catalog.
I will definitely take your and Frankie's advice to change them back to progressive.
We actually have a active chapter of NCRS here in Perth with some very knowledgeable people, including mechanics, auto-electricians, etc. Most have quite original mid-years, so my '58 with many non-original components (like block, camshaft, carbs, etc) sometimes causes questions.
We meet every Saturday morning, so if I stuff up the setup I'm only a few days of rough running away from getting invaluable guidance.
I replaced the set of NGK XR5 (one heat rating less than XR4) in there with NGK BP5S, as it was the equivalent of AC Delco R43S shown in the Zip catalog.
Any of these would seem to do the job.
David
WAY too cold a plug on a dual quad car IMO. Most run ACR45S; the NGK-XR4 covers the 45S and 46S heat ranges and work nicely...
02-12-2015, 04:23 AM
Dual Carter WCFB setup question
