How to rebuild a Rochester 2GV Carburetor - a pictoral essay... I'm starting this thread because I noticed (after my third rebuild of a Rochester 2GV) that the instructions in the official 1968 Buick Chassis Service Manual are rather terse. All of fifteen paragraphs; just one page of instructions and no pictures. I know two-barrels are simple, but I think that's a bit too little. The instructions that come with a carburetor rebuild kit are even less. An exploded diagram and a sentence or two ("Disassembly: Use exploded view as a guide - Reassemble in reverse order"). Not much to go on for the first-timer. ********** So, you've decided to rebuild your Rochester 2-barrel carburetor. Maybe yours is giving you problems, or is leaking gas, or you want to clean it up, and you simply want to. Whatever the reason, it's not that difficult. The pictures that follow detail a Rochester 2GV as found on my 1968 Buick Skylark 350. However, all Rochester 2-bbls are very similar mechanically and differ primarily in choke mechanisms and venting details. That's not to say they're all interchangeable or that parts can be swapped. But if you're rebuilding a lone carburetor, this guide should help.
Here's what you'll need to rebuild the carburetor. For a part made up of fragile castings, precision orifices and many small parts, it requires some ridiculously large screwdrivers and wrenches. The main thing to remember is that, despite the size of the tools, a gentle but firm touch is all that's needed.
Disassembling anything is generally (too) easy. Using the right tools, a gentle but firm touch and a dip-tank of carb cleaner, you'll have yourself a collection of parts. Do not remove the throttle blade or choke plate from their shafts. Their screws are staked after assembly and need to be ground down before removal. Plus, the throttle blades are fit quite precisely and the mixtures holes drilled accordingly. Generally, there is no need to remove them.
You'll also need a carb-kit, available from your local auto-parts store for under $20. It consists of mainly gaskets, a couple of check valves, accelerator pump, and needle and seat. Typically one kit fits a range of carburetors, so you'll have many more gaskets than shown here to choose from. Match up the old gaskets to the new ones to find the right ones. If in doubt, match the gaskets to the carb body, making sure the gasket fits with no holes blocked off.
Let's begin. Assemble the throttle body by installing two idle mixture screws and springs (left side of pic) into the throttle body. Using only your fingertips on a screwdriver, turn them in until they lightly bottom, then back them out two turns. This initial adjustment is enough for the car to start and run. Final adjustment occurs after the car is warmed up. On the right side of the pic is the PCV fitting (top), installed with a bit of teflon tape or similar sealant. Then install the idle-speed screw and spring. Just a few turns to hold it in - it will be adjusted later.
Now take the appropriate gasket from your carb kit and place it on the float bowl (lying upside down, left side of pic). Make sure all the holes line up. Gently place the throttle body on top.
The throttle body is retained by three large phillips screws, tightened with an even larger screwdriver. The Buick manual says "tighten securely" - don't go any more. The four hex-head bolts are temporary "legs". Though not necessary, they do make it easier to stand the carb on the bench and move the throttle through it's full range of motion. Flip the carb over and stand it on its legs.
Now find the following items in the kit: a T-shape retainer, small spring and steel ball. There are two balls used in this carb, a small aluminum ball and a larger steel ball. The steel one is shinier - use a magnet if in doubt.
The ball is dropped into the accelerator pump discharge hole, followed by the spring and T-shape retainer. These pieces form a one-way check valve to ensure the pump shot goes into the carb and no air is sucked back. Push the retainer flush with the surface, then use the hammer and drift to lightly stake the retainer in place. You don't have to hit it hard - a light tap should do it. You want just enough retention to keep it from springing out before you finish assembly. In fact, there may be enough leftover distortion of the casting to hold the retainer without any further staking.
Next, drop in the two plastic main well inserts. These should fit flush with the surface, just like the T-shaped retainer. Because these pieces are made of plastic, you should not use any kind of carb-cleaner on them - they would only melt. Mineral spirits (or similar) should be used instead.
Place the correct venturi cluster gasket in place. Your carb kit may have several to choose from. Some look identical. This particular one has a slot in the center for an alignment tab. Others do not. Make sure the gasket you choose fits easily.
Here are two venturi clusters, one before and one after being dipped for ten minutes in carb cleaner. What a difference! I highly recommend a dipping tank over cans of spray cleaner. Less messy, no overspray in your eyes or surrounding parts, and they get thoroughly clean, inside and out.
Put the venturi cluster in place. This model has a slot that engages an alignment tab, making for a snug fit. Three screws hold it down. The middle screw is different - it has a wider head, is only threaded halfway, and uses a fiber gasket. Don't miss this gasket since the screw seals up the pump discharge passage and will leak without it.
You'll clean and reuse the main jets and power valve. The carb kit will supply a new gasket for the valve.
The jets and power-valve (with new gasket) get installed in the bottom of the float chamber. They're made of brass which is easily deformed if overtighted. The power-valve is best tightened with a wide-blade screwdriver that has a slot cut in the tip.
Remember those two balls in the carb kit? Here's where you need the smaller, aluminum one. The mesh screen and spring are reused from the carb. There are two similar sized (large) springs. Both are used in the accelerator pump. You need the lighter (weaker) one of of the two here.
This is where they go - the accelerator pump well. The small circle at 5-o'clock is where the aluminum ball will fit. The large spring goes on top, trapping it in place. The aluminum ball forms another check-valve for the accelerator pump, ensuring that fuel only flows into the pump well when you release the gas pedal not out when you floor it.
This is how it looks when they're in place. Both the large spring and the screen mesh are simply pushed in place with your finger for a snug, friction fit. The screen mesh forms a second fuel filter for the accelerator pump intake. Once these pieces are in place, put the whole assembly to one side.
First, assemble the accelerator pump. Here's where you need the heavier (stronger) of the two large springs. The carb kit supplies the rest. Fit the spring to the pump plunger, then pull up on the shaft while holding the spring down and snap on the spring retainer. Next, fit the pump plunger into the pump lever with the arm pointing inward. Retain the plunger by crimping on a C-clip (from the carb kit) with needle-nose pliers.
