Two Carburator questions
Thread Starter
Instructor
Joined: Dec 2006
Posts: 158
Likes: 0
From: Tustin CA
Two Carburator questions
So, recently I have sold my FJ cruiser and began driving my 77 vette every day (vette was paid off and we are trying to buy a house) and I am getting worse gas mileage than I thought I used to get. I started looking at the carb and there are two things that I am curious about. The carb is an edelbrock 1903.
Picture of carb for reference:
http://i223.photobucket.com/albums/d...8/Carb-mod.jpg
1) In the pic above, what is the circled port for? I had a vacummn cap on it but when I took the cap off, it was filled with gas.
2) Is the circled flap always supposed to be open? From what I can tell it pretty much never closes whether the car is hot or cold. I put an electric choke on recently if that makes any difference.
Thanks,
John
Picture of carb for reference:
http://i223.photobucket.com/albums/d...8/Carb-mod.jpg
1) In the pic above, what is the circled port for? I had a vacummn cap on it but when I took the cap off, it was filled with gas.
2) Is the circled flap always supposed to be open? From what I can tell it pretty much never closes whether the car is hot or cold. I put an electric choke on recently if that makes any difference.
Thanks,
John
Thread Starter
Instructor
Joined: Dec 2006
Posts: 158
Likes: 0
From: Tustin CA
Thread Starter
Instructor
Joined: Dec 2006
Posts: 158
Likes: 0
From: Tustin CA
So I just looked at the car and I do have a PCV valve on the drivers side valve cover and that is connected to a port on the front, bottom, passenger side of the carburator. Is it possible that I have this connected to the wrong port?
If I do, what do I use the port that it is currently connected to for?
If I do, what do I use the port that it is currently connected to for?
Melting Slicks
Joined: Apr 2002
Posts: 2,337
Likes: 14
From: Norfolk VA
If I remember correctly there are actually three ports. The large port in the middle is for the PCV valve. The smaller port on the passenger side is for ported vacuum, and the smaller port on the driver side is for manifold vacuum. This vacuum hose runs to the vacuum advance on the distributor. You can use either, Edelbrock recommends using the ported vacuum port and cap off the manifold vacuum port. Other prefer to use manifold vacuum. It appears most look down on Edelbrock carbs because they are not "performance" carbs.
Last edited by Oldguard 7; Sep 9, 2008 at 07:34 PM.
Le Mans Master
Joined: Dec 2007
Posts: 6,422
Likes: 591
From: McHenry Illinois
I'm not sure what the port is for, but the choke flap should close when the engine is cold. If it's been sitting overnight, pull the air cleaner and look at the choke butterfly(flap). It should be mostly closed and if you depress the accelerator slightly, it should close completely. When you start the engine, the choke pull-off will slightly open the butterfly. Then as the engine warms up the choke opens fully and the engine should settle down to base idle.
Thread Starter
Instructor
Joined: Dec 2006
Posts: 158
Likes: 0
From: Tustin CA
Ok so, I called the Edlebrock tech people and got a diagram for this carb. The port in question is called the "Bowl Vent". After the tech guy e-mailed me we hung up so I didn't get to ask him what that does.
Anyone know what the "Bowl Vent" is for? Should I uncap that sucker?
Reading through the manual I see two other things that I don't understand:
1) Fast Idle Screw - What does this do?
2) Clean Air Port - What does this do?
Thanks in advance guys!
John
Anyone know what the "Bowl Vent" is for? Should I uncap that sucker?
Reading through the manual I see two other things that I don't understand:
1) Fast Idle Screw - What does this do?
2) Clean Air Port - What does this do?
Thanks in advance guys!
John
Le Mans Master
Joined: Dec 2007
Posts: 6,422
Likes: 591
From: McHenry Illinois
The fast idle screw is used to adjust the fast idle. The fast idle is activated when the choke is closed. That is the reason for depressing the accelerator slightly because the fast idle cam will drop down on the passengers side of the carb and come in contact with the fast idle screw. This causes the engine to idle faster for warm up.
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Verdad Gallardo
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Adjusting the carb correctly is a more complicated process than this Forum can really provide online (with a carb we can't interact with). I would suggest that you get a GM chassis Service Manual for your car (specific for your year). In it there is extensive info on proper set up, adjustments and proper connection of vacuum lines. I have an Edelbrock 1901 on mine, and I do not have that upper "bowl vent". Sorry I can't help on that one.
Drifting
Joined: Feb 2005
Posts: 1,879
Likes: 38
From: Los Gatos CA
I believe the Bowl Vent is acually the fuel bowl vent. That's why there was gas in the cap. The car (or truck) the carb was designed for used it, but your Vette probably won't. Cap it off. You have a very good carb; get it set up right.
Drifting
Joined: Aug 1999
Posts: 1,468
Likes: 1
From: Kirkland WA
The tube pointing straight up is the bowl vent and don't cap it. It's to keep the carb from pressurizing since these don't have fuel return lines. The gas is vented back into the intake stream, underneath the air cleaner, so there would be no way to hook it up to anything. Leave it alone 
That 2nd port is clearly a large vacuum port. Could be used for power brakes, PCV, or any number of vacuum accessories. Leaving it open will cause the car to run rough, and run lean (or cause you to adjust the mixture screws to compensate, which if you have done, means the carb is running rich and would certainly affect your gas mileage)
Assuming your PCV hose is plugged in below the fuel filter (and it appears it is), and you don't see any larger Vaccum hoses lying loose (like your brake booster), then get yourself a vacuum cap from the local auto parts store and plug it up. The car should run better.
The large "flap" you're referring to is the choke plate. And it should be pointing the direction it's pointing after the car has warmed up. When the car is cold, that plate should be closed. In the AM, when the engine is cold, remove the air cleaner and push the throttle down once. It should cause the choke plate to snap shut. If it doesn't something is wrong with your choke setup.
That 2nd port is clearly a large vacuum port. Could be used for power brakes, PCV, or any number of vacuum accessories. Leaving it open will cause the car to run rough, and run lean (or cause you to adjust the mixture screws to compensate, which if you have done, means the carb is running rich and would certainly affect your gas mileage)
Assuming your PCV hose is plugged in below the fuel filter (and it appears it is), and you don't see any larger Vaccum hoses lying loose (like your brake booster), then get yourself a vacuum cap from the local auto parts store and plug it up. The car should run better.
The large "flap" you're referring to is the choke plate. And it should be pointing the direction it's pointing after the car has warmed up. When the car is cold, that plate should be closed. In the AM, when the engine is cold, remove the air cleaner and push the throttle down once. It should cause the choke plate to snap shut. If it doesn't something is wrong with your choke setup.
Last edited by Corellian Corvette; Sep 10, 2008 at 02:08 AM.