Technical Upgrade from Rochester 2G to Edelbrock 1406 worth it?

I'd run the float you have. I've rebuilt a LOT of 2G carbs and haven't seen a bad nitrile float in one yet (many in QJets though). Yes, you need new idle mix screws but they can wait...just may not be able to trim the idle mix perfectly for now. Agreed on the metal tubes under the cluster...they were not used in all models of this carb so go without 'em.

 

awesome thanks! Cleaned up parts with carb cleaner and sitting overnight in chem dip. I’ll clean passages in the morning with thin wire and spray again with carb cleaner and put it back together and run what I have. I’ll buy new idle mixture screws and put them in when I get them and run what I have for now to verify I put the carb back together ok.

 

Good for you on carb rebuild!

 

It keeps getting better with this truck. Turns out the carburetor is from a 1969-1970 Chevy application based on the numbers stamped which I could see after cleaning it. I learned the hard way the 1975 rochester rebuild kit from Walker does not work and once opened I can't return it. ugh! Anyways I ordered a new one for the 1969 year and it looks correct in the photos. It doesn't come with the accelerator pump so I ordered one and a brass float. All from Oreilly so I can return the pump or brass float if I change my mind. The idle mixture screws I'll have to get from Mikes Carburetor.

I noticed a couple of things:

1. The old gasket didn't seal around the throttle body and looks like the previous rebuilder didn't use the right one. What performance issue would this have caused and fuel to leak outside the carb? See photo below with red arrows.

2. The idle mixture screws that came out have a taper that look more like the 16-100 idle mixture screws from Mikes Carburetor (which says quadrajet in the listing). I can see the ridge formed on them when they were overtightened (not by me). It almost looks like the screws should have a longer taper based on how it changes angle after the ridge and maybe the carb has shallower port and it formed a new taper angle on the beginning part of the screw when tightened. I can't tell... nor how to find the screws I need given matching what I have may not be correct if the previous owner used the wrong ones. Mikes carburetor does not sell the idle mixture screws by year, nor carburetor number and they suggest matching the taper of the old screw. Most of the screws for the rochester 2G on the Mikes carburetor website seem to have a longer taper than mine. hmmmm

 

Longer taper sounds right for a 2GC carb.

 

The gasket at the red arrows indicates a major air leak and the fuel mix would have been upset as the throttle opened,causing a lean mixture. Also would have allowed unfiltered air into the carb...not good.

 

ah good to know so at least I can hope for better running engine after putting the right gasket on there!

I would have thought it would cause a mixture problem if that air gap was below the throttle blades no? That gasket sits above the throttle blades.

 

It'd certainly cause a major mixture problem at idle and low throttle if it were below the plates-that's correct. As it's above them, the main air leak will occur as the plates are further open and the venturi above becomes a restriction. Air will enter the gap in the gasket and bypass the venturi and main metering circuit, causing a leaner mixture.
If I remember today, I'll pull a mixture screw out of the 2GV I'm running on my Flathead and take a pic of it.


Terry

 

Makes sense thanks and a photo of the idle mixture screw would be awesome!

 

Pic-

 

Big end of the taper starts at .115" and tapers to .035" and is approx 1/4" (6+ mm) long. The carb is a 7041110.

 

Awesome thanks! looks like a longer taper than the screws I pulled out. given how the previous person couldn't even put the right gaskets on I wonder if the screws are wrong! I may buy a set that look like yours and see what it does.

 

I got to jump in here.

First, no offense meant to anyone, but need to set the record straight.

(1) The throttle body gasket MAY or MAY NOT be correct! The gasket does not go by year, rather by application. Forget what the previous rebuilder may have used (he/she may have used a wrong gasket!), buy the correct kit by carburetor identification number, and the correct gasket will be in the kit. The cutouts are vents, basically to eliminate, or minimize hot idle issues. This style gasket was introduced in 1957 (see reference below, with a copy of the original Rochester introduction document). NO vacuum leak is introduced, as the vents are above the throttle plates, not below. When I spoke to a Rochester engineer about these gaskets some 4 decades ago, he informed me that the vents are in a "dead" area of the air stream, and nothing would enter the air stream through the vents, only exit if excessive pressure existed in the throttle area. While not a "hard and fast" rule, the gaskets that completely seal tend to be used on marine applications, where exiting vapors could create an issue. Fuel vapors in a closed bilge are NOT a good thing! If the Rochester engineers designed the carburetor in question to use the vented gasket, using the sealed gasket can cause the calibration to be way rich at idle and off-idle in hot temperatures or using high-volatility fuel. Rochester is not the only carburetor company to use vents in this manner. Both Carter and Stromberg had open drilled vents (that some enthusiasts feel should be sealed) to accomplish the same goal. These gaskets also come in several thicknesses. If the carb is one with a divorced choke, using the wrong thickness will change the operation of the choke.

https://www.thecarburetorshop.com/Ventedgaskets.htm

(2) Idle mixture screws, like the gasket, are by application, not by year; although in general the taper on 1968 and newer idle mixture screws tends to be longer than on 1967 and earlier. The reason - smog emission. The longer taper gives a more precise adjustment for idle emissions. As to acquiring these, they are included in the better carb kits, when the kits are ordered by carb identification number. There are several different idle mixture screws for the various 2G series carburetors, different tapers as well as different lengths.

Jon

 

One other possible issue:

I reread the thread, and see the OP purchased a new float.

Two possible problems with this:

(1) There a number of different floats used in the 2G series carbs. To the novice, unless compared side by side, they pretty much look the same, will normally fit in the carburetor, but correct float level and drop can be impossible.

(2) One needs to check the origin of the "new" float. Whatever those across the ocean use for solder will develop pinholes in 3~6 months if ethanol contaminated fuel is used.

A used carb at a swap meet of the same identification number may be a better investment. Or best, if you can find it, would be new old stock made in the USA 30 or so years ago. Again, to get the correct float, you need the carb identification number.

Jon

 

^^^ Glad Jon is here!

 

Thanks for all the great info! With the stamped number on the carb I found it’s a 1969 year. I bought the correct walker carburetor kit. There are three gaskets, two of which fit correct and one has the opening like you had mentioned referenced in previous post with red arrows the other completely seals it… I’m guessing to use the one with open vents? I don’t trust the previous builder.. at all!!!!! The Venturi cluster bolts were incorrect.. the fucktard used the skinnier center bolt with rubber washer to tighten the float bowl and used the wrong center bolt so maybe that was part of the issue with how it was running before… on top of that he/she must have misplaced a bolt and used an oversized threaded into the housing to make it look like it was doing something..

I decided to use the same nitrile float…and returned the brass one.


this truck supposedly made it to Baja California and was worked on there.. the price of this truck was too good to pass when I bought it 7 years ago but I found out the hard way there’s a reason they do things a certain way down there!

 

What is the stamped number on the passenger side of the bowl?

Jon

 

7029102

two questions I still have are which gasket from the kit I should use, I got the walker 15464B kit and what idle mixture screws I should buy online given I may not want to match what I pulled out given I don’t trust who put this carb together.

 

Gasket 7015106, correct for 7029102, is a thin gasket, approximately 0.030 inch and does have the two cutouts. That is the one I would use, unless you are putting this thing on a boat.

Idle adjusting screws are 7013116.

Jon

 

I’ll use the one with cutouts and order the screws with that number online. thanks!

 

forgot one other question do I just need the thin base gasket for the intake? The walker kit came with a thick spacer which I’m guessing is for people who experience vapor lock and maybe I won’t need it?

 

Forgot to ask, since I'm in San Diego and I usually don't drive the truck when its cold out should I bother with the vacuum break? For now I unplugged the vacuum line and used a cap on the port and wired it shut so the choke plate stays vertical and doesn't move at all, or should I replace the vacuum line and connect it back up and remove the bailing wire?

I was not planning to bother with putting a divorced choke in it.

 

If your temps are warm enough that the engine runs ok without the choke, the vacuum break is unnecessary.

 

Thanks! Usually only drive this thing when its warmer than 50 degrees Fahrenheit outside just by habit and being in San Diego. Most of the time 60s or 70s at least.

 

I mean. I live near Kansas City. And I havent bothered to hook up the choke on my 53 Bel Air yet. As long as fuel pump is good and engine is timed right I've never needed a choke. I imagine in your warm conditions you wouldn't really need one either.

 

Chokes were put on carburetors for a reason, to enrich the fuel calibration on a cold engine, promoting driveability.

A secondary function is the choke butterfly acts as a "straightening vane" to minimize the effects of lower RPM eddy currents in the incoming air; thus actually improving the air flow. With yours wired open, you will still have this benefit.

Lots of folks don't "need" chokes.

Lots of folks don't approach the driveability or fuel economy that I have with my engines.

Jon

 

Thanks so much for all your valuable insight!

 

Had many people tell me this over the years when they heard my choke wasn't hooked up or gone altogether. Yet my cars always still had a quicker startup and smoother idle. On said 53 I went out in 30° weather to start it up for the first time in over a week. Let the pump prime and blipped the throttle once and it fired up with barely a noise from the starter and settled into a nice easy idle. Ill eventually get around to hooking up the choke but it is no priority at all

 

I put it all together and fired the truck up and it idled ok but a little more rough after a couple minutes.. I shut it off and looked and could see a bit of fuel on the intake manifold and some dripping over the throttle blades. It looked like a little fuel came out of the pump rod actuator.

I'm guessing its flooding... I set the float drop to 1 3/4 and float level 3/4 inches. I noticed it was way off before... but wonder if maybe it was set up correctly before and maybe I'm using the wrong numbers. hmmmm. I used the new seat and needle from the walker kit and am sure I installed the clip correctly. I reused the nitrile float. I was very careful to pull the float out any time doing an adjustment so as to not mess up the needle and seat.

The only thing I can think of is maybe with 4.5 psi stock chevy fuel pump I got from Napa maybe the 1 3/4 and 3/4 values aren't good to use? I also may need to re-check the fuel pressure.. I had read 4.5 psi with the carb before I rebuilt it...

 

I have ceased to be amazed at fuel pressures of new pumps produced in the last 8~10 years, regardless of the name on the box.

Your idea of checking the pressure is a good one.

Jon