Is there anybody on the Forum that has a wide experience with Rochester 2gc carbs? In this particular case I am talking about a twin carb set I acquired many years back from a vendor and have had in storage until I installed them on my Cadillac flathead engine. Fortunately the engine starts and runs but has a idling problem. The carbs were supplied as one with idle and one without which is a progressive carb. So the engine is supposed to idle on a single carb. More recently have decided to focus on getting this idle issue attended to and for some reason have just discovered that neither carb body has adjustment screws to set idle. Am I missing something or is there another way??? Any thoughts would be helpful right now.
There are many carb guru's here that will chime in. Some thoughts here though off the top of my head... Take the secondary carb off and block the plate. See if you can get the engine to run real well on the one carb first, then add the secondary. If at idle there is any vacuum thru the secondary then it would appear that the blades are not sealing which is a must. Attack that first. Do you know what jets are in the carbs presently? Had them apart lately? If not then perhaps you should take them apart and have a look see. Might be cruded up. Accelerator pump may be dried out etc etc etc.
you can contact Charlie Price @ vintage speed ( has web site ) he,s the best and has great videos on 2gc carbs and any parts needed
I am assuming that the plastic has been removed from the carbs. Looking at the runners on your manifold, I would be expecting those two carbs to be the same, on fixed linkage and balanced. Not progressive linkage. But that’s just my opinion. (Others will disagree). There are different types of bases for 2gc carbs, so that may be something to look into.
I'd say there's your answer....you have two secondary carbs. One should have idle mixture adjusting screws/needles. Lynn
It would appear that you have a Frankencarb set-up. The bodies appear to be late 1960's Chevrolet, as do the throttle arms. If original, someone has modified the throttle bodies to have no idle mixture (fine for a trailered racecar that idles at 1500 or more RPM, not so fine for the street). The only Chevrolet secondary carbs were 1958~1961 348 tripower carbs, and these aren't those. As Clem mentioned, with a set-up such as this, best results will be acquired by using solid linkage. Personally, I would suggest starting with the manifold and acquiring some known carbs. Then set the up with solid linkage (idle mixture on both). For street use, I would also leave functioning chokes on both. Jon.
Right now the engine will run but struggles to idle and peters out unless revs are maintained by hand or foot on the throttle. I do own several old 2gc carbs, should I consider trying to transfer one of those bases with idle screws onto what I was told was the primary carb in this twin carb setup??? I like the idea of removing one carb and starting off with a single unit.
Russ - changing throttle bodies is not a good idea. If you have several 2-GC carbs, find a PAIR of exactly the SAME by tag number, and try these. Jon.
OK John, I will take a look thru my stash and see what I can come up with first and see if we can then be ready to keep this conversation moving forward.
Cannot tell much about the intake from the pictures. Not certain the exact year it came out, but one of the early 2x2 manifold for the flathead Caddy was done by Detroit Racing. The carburetors of choice were generally two of the Carter 595s (stock Cadillac) 2-barrels. The Rochesters should work well; but you will find them MUCH easier to dial in if you start with Rochesters from a Pontiac, Oldsmobile, Buick, or Cadillac rather than Chevrolet. The Chevrolet carbs can be tuned to run equally as well by a Rochester guru, but will require significantly more tuning because the Chevrolet fuel curve is significantly different from the others. The less tuning required....................well, means less tuning (and purchase of tuning parts) is required. Also, while the Rochesters with the air bleed idle control can certainly be used; using a pair with a conventional idle system is easier (unless you have a radical cam, in which case the air bleed becomes quite useful). Rochester tuning parts ARE available, just much less available than those for Holley. Before starting this project, I would suggest acquiring a copy of the Doug Roe/Bill Fisher book "Rochester Carburetors" and doing some study to understand how Rochester did things. Jon.
Forget my last comment above. I have what I have right now and need to fine tune components to move forward without making a career out of it. Maybe my question should be what should be sitting on top of my aluminium intake that would work. Is it possible or even preferred to run 2 x 2gc carbs, both with idle configuration. A local guy here said to me it could be difficult to get an even spread of fuel when idling only on a single idle carby???
I would agree, - fixed linkage, both idling and balanced. Jon also said this, last paragraph of post 6.....
Don't know, as I don't know which Rochesters you have. The Rochesters come in three different patterns, although only two are common, and most refer to them as the large Rochester or the small Rochester. Nothing wrong with using Rochesters, but check the second line in my signature block Jon
OK, no more questions for now at least. Let me review my options and see what I can come up with. Thanks to you all for the education and great advice.
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