[tripwr1964]

i am a little confused where the idle flow restrictors are located in the venturi cluster of a 2gc carb?

planning a some carb tweaking this weekend to get my big cubic inch tripower to idle on the idle circuit better.

so one of the areas i wanted to check is the idle flow restrictors, but not sure where located. I've looked at diagram after diagram....

[Singleton]

This pic isn't a rochester venturi, but basically the same. Restrictor is in the bottom of tube. Don't open them up too much though, just a couple thousandths at a time.


Good info on basic carb operation here:
http://www.hdts.vcn.com/JEEP/ROCHEST...2GC%20CARB.pdf

[Singleton]

It occurred to me after my last post that maybe you were looking for the channel restriction orifice. inside the small hole on lower left and right of venturi.


Another source of 2G info:
http://www.circletrack.com/enginetec...er_length.html

[tripwr1964]

yes the restriction orifice.
ok that what i thought. thk you!

[Tom Vaught]

Typical Idle Feed Restriction (end of the tube) should be no bigger than .038"
That size works well on large cubic inch Pontiacs and Chebbys with a bit of a camshaft in them.

Typical sizes for 350-400 cid engines are closer to .035-.036" orifice.

The Channel Restriction Orifice is another story;

64-65 421 Autos had a .055" Channel Restriction The MTs got a .049" Channel Restriction.

In 1966 for the 421s Channel Restrictions were:
The Autos were .045" , the MTs were .046" and the "AIR" Air Injection Reactor" MTs were .048"

Tom Vaught

[zeebo]

Originally Posted by Singleton

It occurred to me after my last post that maybe you were looking for the channel restriction orifice. inside the small hole on lower left and right of venturi.


Another source of 2G info:
http://www.circletrack.com/enginetec...er_length.html

is there a way you could circle that channel restriction orifice in your pic? thanks

[zeebo]

Originally Posted by Tom Vaught

Typical Idle Feed Restriction (end of the tube) should be no bigger than .038"
That size works well on large cubic inch Pontiacs and Chebbys with a bit of a camshaft in them.

Typical sizes for 350-400 cid engines are closer to .035-.036" orifice.

The Channel Restriction Orifice is another story;

64-65 421 Autos had a .055" Channel Restriction The MTs got a .049" Channel Restriction.

In 1966 for the 421s Channel Restrictions were:
The Autos were .045" , the MTs were .046" and the "AIR" Air Injection Reactor" MTs were .048"

Tom Vaught

do you happen to know the specs on 2GC carbs from the early 70s? for pontiacs? thanks

[Tom Vaught]

I have no data on Q-jets. Any Q-Jets. I could probably make good Guesses on 2 BBL Rochester stuff (based on the TRI-POWER INFO).

Some Data on 421 SD AFBs and GTO AFBs.

I do have original Rochester Products 64-66 Tri-Power Calibration Information (supplied to me when I restored the Tri-Power system on the 65 GTO in the Henry Ford Museum).

I also have a lot of information on Holley carburetors (having worked for Holley carburetor at one time).

Tom V.

[Tom Vaught]

Originally Posted by zeebo

is there a way you could circle that channel restriction orifice in your pic? thanks

Looking at the Cluster (as shown in the PIC:

You have the two large mounting holes at the top edges of the cluster.

Directly below the BIG mounting holes you have two slightly smaller holes.

If you look inside those holes you will see a drilled passage below the gasket surface.

That is where the Channel Restrictions are pressed into the drilled passage.

The Idle Feed Restrictions (that control the fuel side of the Idle Mixture (adjusted by the mixture screws) are the tiny drillings at the end of the small brass tubes in the crimped section.

TV

[Singleton]

Channel feed restriction orifice. Hard to see, but its in there

[Tom Vaught]

Good visual Singleton.

Tom V.

[77 TRASHCAN]

Lets see now...where's that tri-power catagory, so I can easily find this thread in the future???

[Dick Boneske]

Ditto!

[chrisp]

Originally Posted by Tom Vaught

Typical Idle Feed Restriction (end of the tube) should be no bigger than .038"
That size works well on large cubic inch Pontiacs and Chebbys with a bit of a camshaft in them.

Typical sizes for 350-400 cid engines are closer to .035-.036" orifice.

The Channel Restriction Orifice is another story;

64-65 421 Autos had a .055" Channel Restriction The MTs got a .049" Channel Restriction.

In 1966 for the 421s Channel Restrictions were:
The Autos were .045" , the MTs were .046" and the "AIR" Air Injection Reactor" MTs were .048"

Tom Vaught

Idle feed restriction would show up as your mixture screws out very far , is this correct ? TY

[Singleton]

Be careful not to enlarge the channel restriction orifice too much. It may be beneficial to idle, but will also cause part throttle cruise to be richer also. If you are rich at cruise, opening this orifice will only make it worse.

[Singleton]

Just came across this Delco-Rochester Service Manual from 1973 for 2bbl. Great source of information here.http://www.tocmp.com/manuals/Carbs/R...nual/index.php

[chrisp]

Originally Posted by tripwr1964

i am a little confused where the idle flow restrictors are located in the venturi cluster of a 2gc carb?

planning a some carb tweaking this weekend to get my big cubic inch tripower to idle on the idle circuit better.

so one of the areas i wanted to check is the idle flow restrictors, but not sure where located. I've looked at diagram after diagram....

What is the issue you are having ? Are the mixture screws too far in or too far out ? Or something else ?

[tripwr1964]

Originally Posted by chrisp

What is the issue you are having ? Are the mixture screws too far in or too far out ? Or something else ?

just going thru and checking everything in an attempt to get my idle less stinky... about to put a 4barrel on it. i am to the point i don't even want to drive it.

all seems to be inline. idle tubes opened up a bit. power valve is functional (and i cut 5 coils off). no vacuum leaks. idles 840rpm. mix screws functional (1 1/4 turn out). no dripping. checked float levels and put new valves in....

had it out yesterday. cruises great and runs balls out at wot. it idles nice with a little gurgle and pulls decent vacuum (13-14").

i don't know. maybe its in the ignition. sick of touching the carbs. everytime i touch them its 2 new leaks and 2hrs more work to get back to what i was doing... urgg.

little frustration on this end...

[Tom Vaught]

Do you have a functioning PCV system on the car?

If so you might try a set of the California Tri-Power crankcase ventilation air cleaners.
Instead of air being drawn in the engine from a breather in the valve cover under the hood, the vapors are pulled from the carb air horns thru the crankcase and pcv valve and then burned in the engine. Just a thought.

Tom V.

[tripwr1964]

good point tom.

this setup is acting very similar to my '65 setup i had on my 400... hmm
only 2 items in common between them are the PCV valve and distributor/coil (m&m breakerless unit). the mech and vac adv have been modified for this engine, everything else same.

PCV is easy enough to check.

Originally Posted by Tom Vaught

Do you have a functioning PCV system on the car?

If so you might try a set of the California Tri-Power crankcase ventilation air cleaners.
Instead of air being drawn in the engine from a breather in the valve cover under the hood, the vapors are pulled from the carb air horns thru the crankcase and pcv valve and then burned in the engine. Just a thought.

Tom V.