1961 2X4 originals rebuilt
I recently purchased a set of rebuilt original WCFB carbs for my '61. Put them on and the car and it runs great, but the exhaust is like tear gas. I assume it is running rich. Is this something I can adjust myself or do I need a expert. If it is straight forward I would to try to adjust it myself. Thankyou, you guys are great! John.
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Re: 1961 2X4 originals rebuilt
Each carb has 2 idle mixture screws coming out the front. They are to be set so that the vacuum at idle is peak. You will need a vacuum gauge. Also be sure both the idle speed screws are sync'd correctly. You could do it without a vacuum gauge but you would be reading plugs which is difficult to do with the spark plugs under an idle condition. You might also want to run them a tad lean so they don't load up at idle after prolonged periods. -
Re: 1961 2X4 originals rebuilt
Thanks Alexander for that information. I found the 2 idle mixture screws at the base of each carb, but only the front carb has a idle speed screw. Is this correct? Thanks, JohnComment
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Re: 1961 2X4 originals rebuilt
The rear carb usually is the one that has an idle speed setting screw. The nature of the stock "progressive" linkage is that the rear primary is stage one, actuating the front primary at a certain throttle setting is stage two , followed by both secondaries for all sections to reach WOT simultaniously. Some variations by other applications (such as Caddy El Dorado), ran both primaries together, then bringing in both secondaries (two stage). These units idled both primaries or used air idle screws in each carb. Corvettes and Corvette engine powered Chevies all used the three stage arrangement. Most of your normal (?) street driving will be done using just the rear primary (2 barrels) for obvious reasons of economy, and the Corvette manifold lent itself well to adequate distribution. At WOT it has some deficiencies which can be improved by elevating the carbs about 1-1/4" while maintaining the cross cuts, but this is not practical on Corvettes (only on Chevies with the necessary hood clearance). More than you needed to know, right?
Stu FoxComment
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Re: 1961 2X4 originals rebuilt
if the idle transfer slots are open too much you will get a rich idle. make sure the idle jet is .031 diameter not .035 diameter.Comment
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Re: 1961 2X4 originals rebuilt
Thanks Stewart and Clem. These carbs are on a early '61, assembled first week of Oct. 1960. My next question is should both carbs have the idle by-pass screws or just the front (secondary) carb? This screw is located on the L.H. (drivers side) of the base. There is no provision for one one the rear (primary) carb. Wondering if and when this screw was deleted on the rear carb. Thanks again for the help. John.Comment
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Re: 1961 2X4 originals rebuilt
John,
I read these carburetors run rich and any good rebuilder will bring the carburetor back to OEM specs., so after adjusting the emulsion screws for best vacuum the A/F ratio may still be rich.
Clem is right about the idle feed restrictor from .035 to .031 to lean the idle circuit A/F ratio. A good test is after setting the emulsion screws for best idle, increase RPM to 1200 and turn the emulsion screws in 1/2 turn. If the motor speeds up the idle/transfer circuit is too rich. Do this at 1800 and 2000 rpm to see how the motor responds.
The first part of carburetor tuning is the idle/transfer circuit because it's also active at cruise rpm so it affects A/F ratio there also.
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Re: 1961 2X4 originals rebuilt
I was having the richness issue with my 2x4 setup. The previous owner had the carbs rebuilt by so called experts in FL. The engine would idle perfectly but would start cutting out as rpm's increased. I was getting frustrated in trying to diagnose as I could not find anyone whose advice was effective. I finally ran across someone knowledgeable of WCFBs (Ken Irwin 618.435.3728) and he sold me the correct metering rods and jets. The car now runs great although maybe still a little rich (black tail pipe soot which I guess is normal for 2x4's). Given my experience, you may want to check to see if you have the correct metering rods and jets.
GerryComment
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Re: 1961 2X4 originals rebuilt
When the dual 4-Bbl setup made its debut in 1956, both front and rear carbs had idle mixture adjustment facilities. This disappeared circa October of '56 with a carb running change.
As Stu mentioned, it's the REAR carb that had idle mixture provisions for '57L and forward--NOT the front carb. Perhaps that's part of your problem (carbs mis-installed).... At curb idle, the forward carb should be essentially inactive due to the progressive linkage.Comment
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Re: 1961 2X4 originals rebuilt
Thanks Gerry- Small world, Ken Irwin is the guy I bought this set-up from a couple of months ago. Great guy. As I said, the car at idle is fine and it runs great. It's just the exhaust smells rich. A couple of freinds with the same set-up say get used to it, it's just the way they run. Again I'd like to thank everyone for thier help. Think I'll just leave good enough alone. John.Comment
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Re: 1961 2X4 originals rebuilt
If your carb base has the large idle bypass screw on the left side of the base it is a 1956 or 1957 base or carb. These were the only years to use them. Most guys just seat them down snugly and forget them.
Here are a couple of photos of an early '61 set I have. Tag dates are Dec 1960. Both carbs should have an idle adjustment screw and no screw in the side of the base. Refer to page 124 of Nolan's book to see a good clear picture of a '56/'57 set of carbs. I could unbury my '59 and take a picture of a set of '56 carbs if you don't have the book.
TomComment
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Re: 1961 2X4 originals rebuilt
Jack H.;
Thanks for mentioning the 56 set up with the Air Idle screws. I almost for got about those. I only worked on one set on a 56 that was said to have a factory experimental 301 cu. in. engine it. It sure performed well so perhaps there was something to that. At any rate, do you suppose the change over from the air idle screws to the throttle idle arrangement happened at the same time they changed the manifold design under the base of the carbs, i.e. from the four ports to the cross cuts from one primary port to an opposite side secondary??
That was obviously an attempt to improve on the manifold's deficiencies, but only more area above the cross cuts helped. I believe I found this out by goofing off one night when I was installing headers on my 57 Chevy. I ran the engine without manifolds and observed, by exhaust color, that two cylinders were running lean. Using longer studs, I stacked five 1/4" spacers with matching cross cuts under each carb (by trial and error) until I achieved even colored exhaust for each cylinder. About 6 months later, I read an article in a Hot Rod magazine describing the same process and they too arrived at 1-1/4" as the amount needed to rectify the condition.
Stu FoxComment
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