I have a matching set of carbs from a 58 impala still have the metal tags (#'s 015, 017 and 020 if memory serves correct). I ordered the aluminum base kit with progressive linkage from vintage speed (still waiting for the package to arrive), in the mean time I was doing some preplanning in my head and ran across something I would like some feedback on: With the kit you have an extended throttle shaft that has to be installed on the primary carb in order to use the progressive linkage. The thing is the throttle arm (part that throttle cable attaches to and where the pump rod lever for the accelerator pump attaches to) is pressed on rather than attached with a screw. By pressed on I mean at the factory it looks like the throttle shaft extended past the throttle arm where it attaches to the shaft and then some sort of pressure was applies in order to mash the end of the throttle shaft in order to hold it on. Sorry I don't have any pics right now. Should I grind the pressed on piece off and screw into the new extended throttle shaft? (that is if there is a place to screw it in). I may be jumping the gun, all of this could be covered in the instructions that come with the kit but I like to be prepared in case I need to order some additional parts or anything. Anyone have a similar experience? Any positive feedback would be appreciated. Thanks, David
I think that you are exactly right, file or grind away the 'peened' over part of the old shaft, then re-fit to the new shaft, if there is no provision for a screw, drill and tap it, or get a machine shop to do it for you. That is what I did to mine. A good way of sorting out your carbs is to blank off the secondary carb holes on your manifold using two pieces of plate with four bolt holes in. This way you can tune in your primary carb knowing that you don't have air or vacuum leaks on the secondaries, when you have tuned your primary carb, you have no leaks, you have set your ignition timing, gapped your points, set your fuel pressure at no more that 5p.s.i, Your car should run very well on just the primary carb, Do Not attach any vacuum pipes to the secondaries, ever. Then install your secondary carbs, with all the progressive linkages, you're engine's note and tickover should not change as air should be sealed around the butterflies of the secondaries until you give the gas pedal a big boot. This is not all you need to do, there is in the bottom of the accelerator pump bowl a small ball bearing, this ball bearing needs to be glued into place on all three carbs using a 2 pack epoxy glue, this is because you will not be making this work by vacuum any more. All I have said here is stuff told to me by Charlie Price (Vintage Speed), call hime up, very helpfull, nice man.
Oh yeah the primary carb is small base GC and the outer carbs are small base G's, I was assuming everyone knew that already but wanted to clarify. I know there are a lot of other posts regarding tri-power setups, 2g, 2gc carbs, progressive linkages, pictures of linkages, carb bases and etc. I have read most if not all posts regarding anything to do with these subjects that I know of but didn't see an answer to what I was asking. Thanks again, David
Thanks rustycoupe. I feel comfortable with the drill and tap thing. I actually did that on the front carb I originally made my own progressive linkages and attached a homemade throttle arm piece to the front carbs throttle shaft by this process. It worked for a while until the piece ended up breaking. I also decided to buy the kit because I couldn't ever get the butterflies to seal properly (tried the jb weld trick and also lapping in new butterflies). I wasn't aware of the epoxy being applied to the balls under the accelerator pumps...thanks for that information.
I'm confused about the lapping of the butterflies, I believe that when they are fully closed they are sitting in the bores at around 15 degrees from horizontal, this is certain of 2G's any way, so obviously the butterflies are not completely round. You should be able to loosen the butterfly screws and using light pressure on the linkage make the butterflies self centre, then while hold the linkage with light pressure re-tighten the screws, this should make the butterflies seal. I have in the past made new butterflies on our CNC machines, holding them at 15 degrees, they work fine.
When converting to non-factory linkage, one should consider the following: If one looks at the FACTORY rod used from front to rear on ALL Rochester tripowers, and the rod from center to rear on ALL FACTORY mechanical linkage setups; one will notice that one end of the rod or one of the arms is slotted. This slot is NECESSARY because of the coefficient of linear expansion OR written differently: failure to use the slot and provide for heat expansion will cause one set of butterflies ALWAYS to be slightly open, regardless of how well they seal when the carburetor is off the manifold. And why would you want to epoxy the balls under the accelerator pump, thereby preventing the accelerator pumps from functioning???????????????????? Jon.
It's hard to see the screws here but he replacement shafts are drilled and tapped for machine screws. Just grind the end of the shaft to free the lever. The screws hold them on the replacement shafts. The butterflies for the end carbs are thicker than the originals and the center carb so that they will seal better. You will need the hot rod shafts for the end carbs also with the thicker slots for the thicker butterflies. The new thicker butterflies need to be seated into the bore now that the shaft and butterflies have been changed. They come slightly over size just for this purpose. You can see how wide the seal is after it has been lapped in. If you buy the replacement end bases, this has already been done for you. I did a post on this a while back but I can't seem to find it now.
To expand further on the ball beneath the accelerator pump: Rochester used two methods of controlling the fuel flow through the accelerator pump. (1) AND BY FAR THE SUPERIOR METHOD (my opinion, the opinions of bean-counters will differ, as the initial cost is greater). Two balls are used. One ball (inlet) is located beneath the accelerator pump, and the other ball (discharge) is located beneath the venturi cluster. When the throttle is lifted, the pump lifts, causing the ball beneath the pump to lift, allowing fuel to flow from the bowl into the pump well. Since the discharge ball is spring loaded, the discharge ball will be in the closed position. Pressing down on the accelerator will cause the pump to be moved in a downward position, creating hydraulic pressure in the pump well. This pressure will close the ball under the pump, preventing fuel from being moved back into the bowl; and will cause the discharge ball to be lifted off of its seat and fuel can then move from the pump well through the pump discharge jet into the venturi area. (2) The ball beneath the pump is eliminated, and a vertical slot is cast into the the wall of the pump well connecting to the bowl. The theory being that (assuming the bowl is full), fuel will spill through the slot, and fall past the pump skirt when the pump is lifted. In practice, this method will GENERALLY give one FULL pump squirt (subsequent pump squirts may be diminished in volume) until the slot destroys the pump squirt, requiring rebuilding of the carb because the pump has ceased to function. Bean-counters love this method, as it is cheaper to build initially, and creates additional sales through repairs. Jon.
The way it was explained to me is that, the check ball is no longer required if you rebuild the carbs using later type pump seals, as they work in a different way to the original type pump seals, and you are converting from vacuum secondaries to mechanical secondaries. This was explained to me by Charley Price, I too have two Tri-power sets ups for my 348, and they both work fine, one is original 2G's the other set are converted primaries, but both are mechanical progressive secondaries. But as I said mine are 2G's, different carbs to yours, so I may be wrong.
follow the directions suplied w/ the kit...mine work great(why would you use real tri power carbs w/ a change over kit)
One other issue to consider: For those of you who work on carburetors, what is the single most troublesome feature of both the Rochester Quadrajet, and the Stromberg WW? (Hint) Its aluminum, wears profusely, and bushings have to be installed with 90 percent of the rebuilds. Jon.
Hazman, I'm short one dumper carb for my 348-tri power......I'd be interested in buying xtra parts????????
GM tri power carbs have a plastic coating on the butterflies in end carbs to seal off at idle. My Caddy end carbs can be filled with gas in the bores and will not leak past the butterflies.
For those of you who work on carburetors, what is the single most troublesome feature of both the Rochester Quadrajet, and the Stromberg WW? Don't know about Strombergs, but my buddy the Q-jet guru was surprised that the alum throttle body on my Vette's carb had not been worn by the butterfly rods, said it usually was the case. Causes binding of the flys and hi-speed idle problems, typically.
When I built a tri-power on the cheap, I J-B Weld-ed the idle passages in the end carbs and spent a bit of time matching the butterfly's to the bores. The set up ran great, but if you let the throttle slam shut the end carbs stuck, as there were no idle speed screws to prevent it. THIS is the reason for the thicker throttle plates, they also close at more of an angle. P.S. I left all the accelerator pumps stock, you need them so the motor don't fall on it's face when you dump it!
There isn't one problem with Q-Jets, there are a few. I worked in a carb shop for 5 years. The tops (airhorn) on Q-jets normally warp from the two front bolts being torqued down two hard. Sometimes the body will be warpped also. On the bottom of the main body, the two spun over plugs will leak sometimes. The base primary throttle shaft wears due to the big return spring on the passenger side. It loads the shaft on an angle causing it to wear. We had bronze bushings we would install and ream to size. The secondary valve spring breaks sometimes. The fuel fitting cross threads real easy. Once you sort those problems out they run real good.
I've read these threads, some of it is good-some not. I've got a set of Rochester's running with Price's bases--the big bore Pontiac end carbs. I used a std. big bore 2 bbl. (common) in stock form-used an extended shaft base I made-screwed plate into shaft. REASON for Price's bases was vacuum sealing-the std. hipo Pontiacs leaked bad-most of them do. His uses brass bflys & alum. body--lapped sealing which gives good vac. on a small block Chevy-dammed impt. if you want it to ever idle. This setup is like his-I think he gets about $900+ for them. Shop the meets, it can be done. geezer
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