Author Topic: Rebuild of Rochester 2BC on '67 Camaro  (Read 4507 times)

heckler

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Rebuild of Rochester 2BC on '67 Camaro
« on: July 17, 2010, 08:46:09 PM »
This is under the Idle Compensator plate.  Can anyone tell me what is missing?  I feel in a pervious build there were 2-3 other items under this plate.



rich69rs

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Re: Rebuild of Rochester 2BC on '67 Camaro
« Reply #1 on: July 19, 2010, 09:34:16 PM »
Looks to me like you are missing everything that actually makes up the hot idle compensator.

From the Delco Carburetor Models 2G, 2GC, 2GV Service Manual 9D-3 MAY, 1973 Supersedes 9D-3 dated Aug., 1964 the following description of operation of the hot idle compensator and parts are as follows:

During prolonged idling in heavy traffic in hot weather, under-hood temperatures can exceed 200 degrees Farenheit causing severe percolation or boiling of fuel in the carburetor float bowl.  With excessive heat, all fuel vapors cannot be eliminated through normal venting and some will be drawn into the carburetor bore and intake
manifold resulting in over-rich idle mixtures. The rich mixture causes a rough idle and may even cause engine stalling.

The Hot Idle Compensator is used on some 2G carburetor models to off-set the enriching effects caused by these excessive fuel vapors by supplying additional air to the intake manifold when idle air/fuel mixtures become rich due to temperature increase  The compensator consists of a thermostaticallycontrolled valve usually mounted in the area above the main venturi or at the rear of the float bowl. The valve closes off an air channel which leads from above the carburetor venturi to a point
below the throttle valves.


The compensator valve is operated by a bi-metal strip that senses temperature. At a certain predetermined temperature, when extra air is needed to off-set the enriching effects of fuel vapors, the bi-metal strips bends and unseats a valve which uncovers the air channel leading from the carburetor venturi to below the throttle valves.
At this time, just enough air is added to the engine to offset the richer mixtures and maintain a smooth engine idle. When the engine cools and the extra air is not needed, the bi-metal strip closes the valve and operation returns to normal mixtures. Hot idle compensators are pre-set at the factory and require no adjustment.

However, to insure proper idle adjustment, the valve must be closed when setting engine idle speed and mixtures. This can be done by using a screwdriver to press down lightly on the valve for those models with the valve located in the main venturi area (left picture). On those models with the valve located at the rear of the float bowl (right picture), hold spring-loaded button "in" when making the idle settings. If no button is available, remove idle compensator cover and using a screwdriver, press
in lightly on the valve when making idle settings.  Replace cover after completing idle adjustments.
Richard Thomas
1969 RS

heckler

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Re: Rebuild of Rochester 2BC on '67 Camaro
« Reply #2 on: July 20, 2010, 02:30:59 AM »
Awesome reply.  Great info. 

What did you mean by left/right picture?

And where might I get these parts?


rich69rs

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Re: Rebuild of Rochester 2BC on '67 Camaro
« Reply #3 on: July 20, 2010, 03:43:28 PM »
...sorry, the left/right picture referred to two generalized illustrations in the service manual - nothing that shows any particular parts.

I have a spare 2GV that I purchased on eBay a couple of years ago for a source of spare parts since both of my cars (66 Chevelle and 69 Camaro RS) use the 2Bbl 2GV (divorced choke) model.  The carb on the Chevelle has the hot idle compensator, the Camaro does not.  I bought the particular carb on eBay because it has the hot idle compensator if I need parts.  You might look around on eBay and see what's out there.

Other possibility would be to contact any of the carburetor restoration shops that are out there.  You may decide that ti would be money well spent to send your carb to them so they can be sure to fit it with the correct pieces.

Good luck.

Richard
Richard Thomas
1969 RS

heckler

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Re: Rebuild of Rochester 2BC on '67 Camaro
« Reply #4 on: July 21, 2010, 04:10:59 AM »
Now rebuilt.....How do I tune it?  Obviously just adjusting idle screw is not all there is.  Any special tools or tricks?

Thanks!!!!!!!!

heckler

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Re: Rebuild of Rochester 2BC on '67 Camaro
« Reply #5 on: July 21, 2010, 03:46:49 PM »
Also, what of the PCV.  It's a "screw" in?  No parts places have reference for it.  They all have reference for push in.  Is my part correct or is their references wrong?

Screws into carb....

rich69rs

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Re: Rebuild of Rochester 2BC on '67 Camaro
« Reply #6 on: July 21, 2010, 05:30:43 PM »
Suggest starting with the info. in this link, paying close attention to JohnZ's "Timing 101" article.  
http://camaros.org/forum/index.php?topic=5534.0

After that, it really is down to adjusting the idle screws and the idle speed.

I usually start by turning in both idle screws until they very lightly seat and then back them off 1 to 1-1/4 turns.  With the engine warmed up and a vacuum gage connected to intake manifold vacuum, individually adjust the idle screws, slowly, for maximum vacuum.  This should be a good place for an initial drive to check idle characteistics, etc. while actually driving.

With the choke open, engine warm and iidling, adjust the idle screw to set the idle rpm (The specific idle rpm in drive and park are in the specification section of the chassis service manuall) but somewhere around 600-700 rpm in drive, 1000 rpm in park would be close for an inital setting.  This should also give you a fast idle of probably 12-1400 rpm.  

As far as the PCV, you should be able to find one at the parts house.  The 2 Bbl on my '66 Chevelle has a PCV valve that screws into the base of the carb in the back.  Wasn't hard to find locally.

Richard Thomas
1969 RS

heckler

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Re: Rebuild of Rochester 2BC on '67 Camaro
« Reply #7 on: July 22, 2010, 03:48:24 AM »
Thanks a lot Rick for spending your time on my topic...very helpful.

Let you know how it goes.

bowtie68iho

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Re: Rebuild of Rochester 2BC on '67 Camaro
« Reply #8 on: November 30, 2010, 03:02:40 AM »
I know this is months after the last posting, but I figured I'd update it anyway because I have the info requested by the initial poster, heckler.  Carburetor parts for a lot of makes and models (including Rochester and Holley) can be ordered by Walker Products, Inc.  However, I believe they only sell directly to businesses, not individuals (you'll need to check on this).  Their catalog is available online at http://www.walkerproducts.com/_pdf/consolidated/carburetor_component_catalog.pdf
68 NOR SS/RS L48/M35 Convertible
Cordovan Maroon - Special Paint Exterior (black stripes)
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KurtS

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Re: Rebuild of Rochester 2BC on '67 Camaro
« Reply #9 on: December 01, 2010, 03:11:42 PM »
2BC are cheap, just keep looking. Here's one for a 69.  $10.
http://detroit.craigslist.org/mcb/pts/2072909143.html
Kurt S
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