Thread: gm tri-power carb rebuilding

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I am looking for info on rebuilding and converting the end carbs on a gm tri power, rochester 2gv i know that the idle circuits are removed but what else. power valves? i would appreciate any info on this as these carbs are hard to find and pricey.


thanks kurb

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http://www.vintagespeed.com/

This guy's got any thing ya need for a rochester 2G, He also sells a kit for the tri power set up with everything ya need including linkage

Kurb I have a eldenbrock manifold with 3 rochester carbs that I'm willing to sell if you interested. The carbs are in good shape but probably haven't been run in 5 years. They were rebuilt when I bought it . The linkeage arm on one of the carbs had broken and was welded back on(not very good) and part of the progressive linkeage is missing. The manifold is in good shape . If interested let me know.

kurb, I've built several tri-power setups using 2GCs I modified for outboard carbs. A little more information would be helpful in answering your question. Could you provide some specifics on the manifold your planning on using, engine size and mods etc.

to mike p

thanks for the reply, i AM using an edelbrock manifold, on a 350 chev small block it has a mild cam in it. also has headers, this is in a 1931 ford coupe. i have three stock rochester carbs (small bore) and need info on outboard carbs. info on idle circuits,power valve, etc. really appreciate this. info is hard to find

thanks kurb

The mods for the end carbs are pretty straight forward.

After you dissemble the carb the first step is to eliminate the idle and intermediate circuits. All I do for this is remove the idle screws and lightly heat the top of the base (usually with a hand held propane torch) and melt acid core solder into the passages. I've done this on all the ones I've modified and have never had a problem with the solder melting back out.

The next step is often overlooked, and that's centering the throttle plates. Normally when the carbs are mass produced the plates are not perfectly centered, it's not a big deal on a normal 1 carb set up as the throttle plates are always open a little anyway, but if they are used as an outboard carb it creates a vacuum leak and is almost impossible to get a good idle. Simply loosen the throttle plate screws and adjust the plate until you have a perfect fit. One thing you might run into is that some of the latter carbs had the plates held in with rivets. The procedure is the same except you will need to drill the rivets and tap the throttle shaft for plate screws.

As far as the power valve normally I jet the carb down a little and leave the power valve functioning. If you find that this is to rich, simply cut off the spring loaded rod that's in the top of the carb. Do not pull the whole rod assembly out of the carb top as it will create an internal vacuum leak. As the power valve is normally closed and the rod depressing is what opens it this effectively eliminates the circuit.

From my own experience, 350 CI is kind of a grey area as far as the small base 2GC is concerned for a primary carb. The small base carb works well under 350 CI and in most cases on stock 350 CI engines. On larger engines or modified 350s they seem to choke the engine. Normally in this case I use a large base 2GC as the primary carb. This requires making an adaptor plate to make up the difference in the bolt patterns. I usually use a 3/8 piece of aluminum and recess the screws to hold it to the manifold and then drill and tap for studs to hold the carb. I then use a die grinder to blend the ports. While the majority of the small base carbs have a side inlet for fuel the large base use a front inlet. In some cases the carb spacing is such that you can use a 90 degree adaptor but in others you will need to modify the fuel inlet. In those cases, I normally remove the inlet fitting (the large one that holds the fuel filter in) and braze the inlet closed. I then drill and tap for an 1/8" pipe fitting in the side of the housing. As the Large 2GC is a little taller and then the adaptor plate is under it, I raise the outboard carbs by simply using the thick base gaskets normally found on the late 70s applications.

The final thing will be dialing it in. I have yet to find a source for off the shelf jets or power valves. The jets that I have come across have run from 43s to 52s. The good news is that jets and power valves are interchangeable between the small and large base carbs. The small jets are found in the carbs used on some of the early 70s V6s and the larger ones are found in the large base 2GCs (2BBL Pontiac 400s are a good source for 52s).

Hope this helps, depending on how much modification you do it can be a little time consuming, but if your doing your own work it's really not expensive (your main cost will be $10-15 dollars for a rebuild kit). I really love my tri-power setups, once they are dialed in there just about maintenance free and there's nothing like the feel or sound when everything opens up.

to mike p

thank you for the info, it looks like it will be very helpful. the motor in my coupe is a low compression unleaded fuel 1974 motor.other than the speedway cam, headers, 194 heads, it is basically stock. do you think i will have problems with the center pot being a small one, or should i run the large base. also do you have any photos of progressive linkage to use with the stock rochester linkage or? i really appreciate this info! its rodders like you that make this a neat hobby

thanks kurb

If it was me, I think I'd set it up with a small base to begin with and see how it does. I's start with a large base power valve and about 48 jets.

There are 2 basic types of progressive linkage I use. The first one uses a seperate piece of linkage from the center carb to each outboard unit (a lot like the early Ford FE tri-power linkage)..

This particular unit is on a HEMI thats going into a 57 Plymouth. On that car the linkage from the peddle pushes instead of pulls, which is why there no provisions at the top of the linkage for a peddle hookup.

The second style uses a single link from the center carb to the front carb, then a drag link that that open the rear carb.

to mike p

thank you again, will let you know how all this works.

thanks kurb