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Old 11-23-2011, 10:03 AM
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Edelbrock carb problem

Hi all

I have an Edelbrock performer 4bbl on my SBC. I noticed that when I open the throttle, I get the normal spray of gas into the primarys, but then I see a couple of large drops of unatomized fuel drip down from the primary venturi clusters onto the air valves...

Why is it doing this? and, are the parts necessary to fix that problem included in the carb rebuild kit (#1477) ?

Thanks

Mike

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Old 11-23-2011, 11:34 AM
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Quote:
Originally Posted by MJS69
Hi all

I have an Edelbrock performer 4bbl on my SBC. I noticed that when I open the throttle, I get the normal spray of gas into the primarys, but then I see a couple of large drops of unatomized fuel drip down from the primary venturi clusters onto the air valves...

Why is it doing this? and, are the parts necessary to fix that problem included in the carb rebuild kit (#1477) ?

Thanks

Mike
Probably nothing, since you're looking at the carb, I'd assume that unless you've been bungee corded onto a fender, this is being done in the shop not on the highway. If in the shop; there is no load on the engine so it will rev very high on very little throttle hence very little air flow through the venturies. What's most likely is happening is that the air flow just gets to a point where it will cause the main circuit to begin to meter but there isn't enough air flow nor time for the emulsion circuit to emulsify the fuel before it starts to feed the booster venturi. So you get a drip, this probably doesn't happen going on the road where the engine is carrying the resistance of the vehicle so it takes a lot more throttle opening with greater air flow to get to the same RPMs you see in the shop with hardly any throttle opening. This situation on the road will get the emulsion circuit going so as to deliver fuel ready to mix with the passing air stream instead of dribbling globs of fuel as you're seeing.

Bogie
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Old 11-23-2011, 12:12 PM
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Thanks for the reply...

It does hesitate and bog down on low end acceleration, and my oil smells like gasoline. I've tried leaning out the fuel mixture, but this has no effect...

could this be an accelerator pump issue possibly?
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Old 11-23-2011, 01:37 PM
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Quote:
Originally Posted by MJS69
Thanks for the reply...

It does hesitate and bog down on low end acceleration, and my oil smells like gasoline. I've tried leaning out the fuel mixture, but this has no effect...

could this be an accelerator pump issue possibly?
Not unless the check valve was allowing fuel to be siphoned from the accelerator pump circuit. But if that was happening, you'd likely also be having accelerator pump problems like delayed flow or no flow.

More likely it's a float, float level, or needle and seat problem that's allowing the float level to be excessive.

I would check to be sure the needle and seat isn't fouled w/anything (teflon tape scraps are a BIG culprit if you've used it during the carb/fuel system install), be sure the float hasn't taken on fuel and become heavy, and be sure the float level is set correctly.

Is the engine cammed up w/a lot of overlap? Does it idle normally or is it rough and "lopey"? Are the idle mixture screws responsive (as in do they change the idle considerably if turned in or out)? The initial ignition timing can be tweaked to help if any of those things apply.
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Old 11-23-2011, 01:41 PM
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Quote:
Originally Posted by MJS69
Thanks for the reply...

It does hesitate and bog down on low end acceleration, and my oil smells like gasoline. I've tried leaning out the fuel mixture, but this has no effect...

could this be an accelerator pump issue possibly?
Bogging on acceleration can be too little or too much accelerator pump and or the secondary air valve coming open too quickly.

The bog:

Lean Bog is a hard studder which may be accompanied with a back fire through the carb. A secondary air valve opening too quickly will also feel like this.

Rich bog is a blubbery feeling that studders but does so more softly and it won't backfire.

Jetting the Edlebrock consists of messing with the float level, being sure the pump pressure isn't excessive, then gets to jets, metering needle and the needle spring under their vacuum piston on the primary side. On the secondary the needle can be sized and is moved by the air valve so again the counter balancing trim on the air valve is important so the valve open with slightly less proportion than the air demand of the engine.

The tapers and steps on the needles reach into what would be an excessively large jet for a Holley that doesn't use needles to fine tune the jet but has a separate power valve circuit form the fixed main jets. The Carter and the Q-Jet use a tapered and stepped needle to obstruct flow through their jet. Essentially there is a position for light throttle cruise most large diameter, a position for high speed cruise a slightly smaller diameter, then a position for max rich power which is the smallest diameter. On the primary side, the position of the metering needle (rod) is managed by manifold vacuum pulling a piston against a spring. The strength of the spring needs to be coordinated against manifold vacuum which is mostly controlled by the cam. The wilder the cam the softer the spring needs to be as wild cams reduce manifold vacuum so a strong spring will raise the metering rod into the rich power setting too early such that you could get fast cruise or even max rich power when all you're doing is slow cruising.

Contact Edlebrock after you test for fuel pressure and manifold vacuum then talk with their tech help desk, they're good people that can aim you in the right direction for a tuning kit.

Bogie
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Old 11-23-2011, 02:08 PM
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Thanks...I'll check all of that when I pull it off next month for a rebuild...

Quote:
Originally Posted by cobalt327
Is the engine cammed up w/a lot of overlap? Does it idle normally or is it rough and "lopey"? Are the idle mixture screws responsive (as in do they change the idle considerably if turned in or out)? The initial ignition timing can be tweaked to help if any of those things apply.
To be honest, I don't know a great deal about the specifics of this particular motor...It was in the vehicle ('79 T/A) when I purchased it and the previous owner bought it that way as well, so he wasn't much help...I really wasn't too concerned about it either, as I'm building a Pontiac 400 to replace it with....and on the whole it seems to run pretty well as is...

My best guess is that it has a mild aftermarket cam...it has a bit of a lopey idle and seems to have a noticeable power curve kicking in around the 2000rpm range. Externally it has the Edelbrock carb, weiand dual plane aluminium manifold, and headers.

The mixture screws are responsive...adjusting them changes the idle noticeably. As far as the initial timing...I'm in a grey area there...whoever installed the engine in this car did it in such a manner where the accessory brackets conceal the timing marker and harmonic balancer. I haven't experimented with the timing yet as I figured my carb is the primary problem...
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Old 11-23-2011, 02:18 PM
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HERE is the Owners Manual. Accelerator pump adjustment is on page 8. The accelerator pump could be the problem if you're having a flat spot or bog right at the hit of the throttle. Or this could be timing. I always advise guys to get the timing curve sorted out, THEN tune the carb.

Towards the back there are graphs showing the changes needed to alter the air/fuel ratio where it's needed. One other thing- if the engine vacuum is too low to hold the rods down at idle or under light throttle cruise conditions, the step up springs may be too strong or there's a vacuum leak somewhere, or the timing is retarded. If the rods aren't seated at idle and light throttle cruise, the air/fuel ratio will be too rich.

If you don't know what jets, step up springs and rods are in it now, it's always a good idea to baseline it back to stock before changing anything. The various tuning kits contain all the rods, springs and jets to tune the carb within reason. In other words, if you need to go outside the calibrations that the kit covers, you probably have the wrong carb for the application.

The p/n 1477 you mentioned above is a master rebuild kit. It contains gaskets, needle/seat, etc. but it does not contain any tuning parts like jets, rods, springs like the tuning kits. So unless the problem were a gasket leak or worn out/faulty needle and seat, the kit won't help the problem. It IS needed (or the simpler gasket kit) to replace any gaskets that might get torn when you take the carb apart to check or change jets, adjust the float or the needle and seat.

There are several tuning kit part numbers depending on your carb number.
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Old 11-23-2011, 02:41 PM
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You NEED and to understand that Edelbrock IB that Cobalt linked

Depending on the camshaft, you probably need to look at, first of all, the springs under the fuel rod piston, then determine if you have the right primary jets then the metering rods. As far as the float, that seldom needs any thing more then adjustment back to the factory setting, 7/16" with a drop of ~1". There are three holes to set the accelerator stroke - as shipped it's the center.

To do the adjustments, you will need the tuning kit, not the rebuild kit (unless it's really cruddy). Assuming you have the 1405 or 1406, 600cfm carb, the 1479($60) kit will give you the most/best choices while the 1487 is usually for a basic stock, or almost stock, engine.

As far as cruddy, this 1405 of mine wiped clean last week with just some solvent. I reset the float, checked and cleaned the rest of the internals then reassembled without that $35 kit:




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Old 11-23-2011, 02:45 PM
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If you are getting a visible flow of fuel when its idling, you may have sucked something into the carburetor and one of the passages is plugged. I managed to pull some RTV gasket shards into mine once and it made it run much richer on one side of the primary. When i pulled off the top of the carb I found a sliver of RTV stuck down in the carb. I discovered the puddle of fuel on one side (using a mirror to look straight down the carb) because that was the troubleshooting the Edelbrock tech suggested after I described the symptoms.

If you have a part throttle bog you need to work with the step-up springs before you mess with the accelerator pump. With a 5" spring my truck has an incredible bog and feels like it might quit completely. When I swap to a 7" spring the bog goes away completely and its like the carb has miraculously fixed itself. I watched the AFR gauge when I had the 5" spring and on acceleration it would spike to about 22 (very lean) for a second or two before power mode would kick in. With the 7" spring it still spikes the AFR, but transitions to power mode so quickly that you can't really feel the power drop.

Bruce
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Old 11-23-2011, 05:28 PM
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Thanks for the replys everybody....

Quote:
Originally Posted by cobalt327
I always advise guys to get the timing curve sorted out, THEN tune the carb.
Any suggestions for a good way to verify timing without being able to see the harmonic balancer or timing marks?
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Old 11-26-2011, 02:08 PM
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Quote:
Originally Posted by MJS69
Thanks for the replys everybody....



Any suggestions for a good way to verify timing without being able to see the harmonic balancer or timing marks?
Sure:

DETERMINE TDC. This will also allow you mark the damper w/a line indicating TDC along w/either making or buying a timing pointer. Then if you
MAKE A TIMING TAPE, you can use it to determine the timing. Timing tapes are also sold, just get one that matches your damper diameter so it's accurate.
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Old 11-27-2011, 10:23 PM
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good articles, thanks for the reply....

Main problem is that the damper is totally obscured from the top and both sides...I'd almost have to do it from underneith the car...Option #2 would be to remove the power steering pump and bracket, then I would be able to see the damper...I think I'll try that....
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Old 11-28-2011, 05:52 AM
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Just a thought.

Quote:
Originally Posted by MJS69
good articles, thanks for the reply....

Main problem is that the damper is totally obscured from the top and both sides...I'd almost have to do it from underneith the car...Option #2 would be to remove the power steering pump and bracket, then I would be able to see the damper...I think I'll try that....
Any way to use mirrors? Consider setting up the pointer and damper line on the bottom where it's not hidden and use an adjustable makeup mirror for viewing it from up top.

If you had an identical diameter accessory pulley that matched the diameter of the damper, it could be used. But belt slippage would throw it off.

The flexplate/flywheel can be used, but you'd be back under the car again...
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Old 11-28-2011, 12:30 PM
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Quote:
Originally Posted by cobalt327
Any way to use mirrors? Consider setting up the pointer and damper line on the bottom where it's not hidden and use an adjustable makeup mirror for viewing it from up top.

If you had an identical diameter accessory pulley that matched the diameter of the damper, it could be used. But belt slippage would throw it off.

The flexplate/flywheel can be used, but you'd be back under the car again...
I could mark the damper and then make a coresponding mark on the pulley...I'd be able to see it then...
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Old 11-28-2011, 02:27 PM
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Quote:
Originally Posted by MJS69
I could mark the damper and then make a coresponding mark on the pulley...I'd be able to see it then...
Absolutely, if you're talking about the pulley attached to the damper- which I'm sure you are. That will work fine.
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