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Old 07-10-2010, 02:08 PM
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3 duce Rochester Help Please

I have a 350 chevy with a 3 duce rochester setup on it. All three carbs where sent to Carb shop and rebuilt alont with the linkage and its progressive linkage. Up on start up it runs fun idles fine. After 5 minutes of driving the engine loads up with to much fuel and will not run right. i took off all air cleaners and on the front carb gas is just drippin down from the two ports inside the carb... So i took carbs apart and made sure nothing was in side the needle and seat and float is at 7/8'' from gasket to middle sodder joint and put back together. ran it and still does the same thing so i put a new needle and seat in and still runs gass down out of ports. I am at a loss for what to do next. Idk if my carborator is junk or what so. if someone has a different direction for me to go please let me know I would appricate it thanks

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Old 07-10-2010, 07:04 PM
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If there is no crud on the needle seat then, Are the floats adjusted correctly ?

What is the pressure from the fuel pump? You want 5lbs or less.

The Carb Shop should have some info on adjusting the floats,
I know it's in the Knowledge Base but I don't have the time to look right now.
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Old 07-10-2010, 11:22 PM
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thanks

i havent checked fuel presure yet but no crud was in needle and seat... I am just running a stock fuel pump and have readjusted float level too and nothing is workin so thanks for you info!
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Old 07-11-2010, 01:54 AM
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Quote:
Originally Posted by brettju5372
i havent checked fuel presure yet but no crud was in needle and seat... I am just running a stock fuel pump and have readjusted float level too and nothing is workin so thanks for you info!
Did you shake the float to be sure it hasn't taken on fuel and become "heavy"? This can cause the float to sink under the weight of the fuel inside of it- causing a too-rich condition.

Check that the bleeds are not occluded or damaged to cause the opening to be too small. Less air through the bleed = more fuel to air. Until the engine is fully up to temp, this wouldn't be as noticeable.
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Old 07-11-2010, 07:06 AM
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Quote:
Originally Posted by brettju5372
I have a 350 chevy with a 3 duce rochester setup on it. All three carbs where sent to Carb shop and rebuilt alont with the linkage and its progressive linkage. Up on start up it runs fun idles fine. After 5 minutes of driving the engine loads up with to much fuel and will not run right. i took off all air cleaners and on the front carb gas is just drippin down from the two ports inside the carb... So i took carbs apart and made sure nothing was in side the needle and seat and float is at 7/8'' from gasket to middle sodder joint and put back together. ran it and still does the same thing so i put a new needle and seat in and still runs gass down out of ports. I am at a loss for what to do next. Idk if my carborator is junk or what so. if someone has a different direction for me to go please let me know I would appricate it thanks
this is kinda funny....I'm having the same trouble. I did the same...I took the carbs apart checked everything twice, and no problems found. But I was at a car show recently and after talking to a few gentlemen, they only run 3-4 psi to the carbs. I haven't had time to check my fuel pressure yet but I may do it later today. I'll let you know what happens.
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Old 07-11-2010, 08:59 AM
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The poster that just had the tri-power rebuilt I would go back to that person, just to get some suggestions.
After all he did rebuild the carbs and I would think that ment functional carbs.
Second suggestion would be tighten up the float adjustment on that bad actor. If the adjustment is 7/8 increase it to 1, make it close sooner check to see if the amount of drip changes, or stops. If you can not get the float to stop the drip then the problem is else where.

The progressive linkage, does it pull the outboard carbs in after the primary carb is 1/2 open? Dripping should have a loading effect at idle more so then driving, the reason being air to fuel ratio .

Fuel pressure to high .. why would it only have an effect on 1 carb, that same pressure is present to all three carbs.
How is the fuel being fed, fuel block 3 lines, or daisy chained off the front carb ?

Just a few things to keep in mind as you go..

Last edited by pepi; 07-11-2010 at 12:09 PM.
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Old 07-11-2010, 09:58 AM
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carbs

I am feeding the carbs with a fuel block with three port fuel block goin to carbs. Yes the progressive linkage opens the other two carbs bout 4500rpm then the other two open up.
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Old 07-11-2010, 10:03 AM
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Pepi is correct,
but on the float you want it lower to close it faster with a 1" drop or more
I/2" will make the float higher for more gas in the bowel

Here is a site that has the manual on Rochester Carb's, there is more to the adjustment it's explained in the down-loadable manual.

This takes you to the page,
http://www.oldcarmanualproject.com/m...3__2G_0005.htm
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Old 07-11-2010, 10:22 AM
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Taken from the site Old Car Project:
The float bowl on Vega 1-1/4" 2GV models (See Figure 3) is externally
vented by a pressure relief valve through a tube mounted in the carburetor
air horn. On cars shipped vertically by rail (VERT-PAK), a connecting hose is added from the pressure relief valve tube to the vapor canister to transfer any raw fuel that may be present in the float bowl to the vapor canister.
The Model "G" 2-bore carburetor has an idle system to supply the correct
air/fuel mixture ratios to the engine during idle and low speed operation.
The idle system is necessary during this period because air flow through the carburetor venturi is not great enough to cause fuel to flow from the main discharge nozzles. Each bore of the carburetor has a separate and independent idle system.

IDLE VENT VALVE (Fig. 4)
In the conventional idle system, during curb idle the throttle valves are held slightly open by the idle speed adjusting screw or, in some applications, by the idle stop solenoid. The small amount of air which passes between the throttle valves and bores is regulated by the screw olenoid plunger to give the engine the desired idle speed.

Since the engine requires very little air for idle and low speeds, fuel is added to the air by the application of vacuum (low pressure) from the intake manifold, directly through the idle system to the fuel in the carburetor float bowl. With the idle mixture screw holes located in a high vacuum (low pressure) area below the throttle valves and the fuel in the float bowl vented to atmosphere, the idle system operates in the following manner:

Fuel from the float bowl flows through the main metering jets into the main fuel well. It is then picked up and metered by the calibrated orifice at the tip of the idle tubes. It then passes up the idle tubes and is mixed with air from air bleeds located at the top of the idle tubes and in the idle cross channels in the venturi cluster casting.
The mixture then passes downward in the idle channels through a calibrated restriction to the off-idle discharge holes or port located just above the throttle valves. Here the fuel mixture is again bled with air and then moves to the idle mixture screw holes where it is discharged and blends
with the air passing the slightly open throttle valves and enters the intake manifold as a combustible mixture.
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Old 07-11-2010, 12:03 PM
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the front and rear carbs do not have a idle circuit or choke. They are secondary only. If you have idel circuits in yours that could be the problem.
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Old 07-11-2010, 02:01 PM
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65ELCMO is correct. If you have 2GC's as all three carbs, you need the tri-power conversion kit. Speedway has it. The center carb only has choke and idle circuits.

Speedwaymotors.com/Rochester-2G-Tri-Power-Base-Kit

Rod and Custom 3x2 2GC conversion kit article

Also
Check your float for pinholes, notice the corrosion on this one.
To check remove float and shake listen for fuel inside, you can also immerse float in warm water to see if bubbles come out. If float has a hole you can drill a small hole to drain fuel carefully. Always drill with hole to the top as drill can ignite fuel. Drain and re-soldier the hole, retest in warm water.


Always flush new fuel lines before use as there can be filings and dirt in the lines even if they are new. This keeps the needle and seats from sticking.

By your first post I would think your floats are too high or the needle tabs on the floats are bent, the tabs should be level with the float seam.

Last edited by Two8tyThree; 07-11-2010 at 02:21 PM.
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Old 07-11-2010, 02:20 PM
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Quote:
Originally Posted by cobalt327
Did you shake the float to be sure it hasn't taken on fuel and become "heavy"? This can cause the float to sink under the weight of the fuel inside of it- causing a too-rich condition.

Check that the bleeds are not occluded or damaged to cause the opening to be too small. Less air through the bleed = more fuel to air. Until the engine is fully up to temp, this wouldn't be as noticeable.
If you find fuel in the float, make the hole where it is leaking a bit larger (do not create yet another hole). Then shake the fuel from inside the float.

You may find that the area surrounding the pinhole is weakened excessively by corrosion. This may be on the inside, hidden from view. If this is the case, it's pointless to resolder the float- you need to replace it.

After drying in the sun (hole in the "up" position) for a few hours, bring the float in and solder the hole up.

You will find that the air will try to bubble out of the float through the solder as the solder cools and hardens. It is tricky and may take retouching the repair to assure the hole has well and truly been sealed. When done, you should have a smooth, shiny repair, w/o any indentation over the hole or a dull graininess to the solder- this is a "cold joint".

Wipe off all the flux (only use rosin flux) using acetone or lacquer thinner to remove all traces, then submerge the float into a container of water to check for leaks by gently squeezing it to cause the sides of the float to flex enough to expel bubbles if there's still a leak.
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Old 09-15-2010, 02:10 AM
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Quote:
Originally Posted by brettju5372
I have a 350 chevy with a 3 duce rochester setup on it. All three carbs where sent to Carb shop and rebuilt alont with the linkage and its progressive linkage. Up on start up it runs fun idles fine. After 5 minutes of driving the engine loads up with to much fuel and will not run right. i took off all air cleaners and on the front carb gas is just drippin down from the two ports inside the carb... So i took carbs apart and made sure nothing was in side the needle and seat and float is at 7/8'' from gasket to middle sodder joint and put back together. ran it and still does the same thing so i put a new needle and seat in and still runs gass down out of ports. I am at a loss for what to do next. Idk if my carborator is junk or what so. if someone has a different direction for me to go please let me know I would appricate it thanks
Have you corrected the problem yet !!!
We like to know what you did to correct this rich condition !
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