750 Eddy Carb issues

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Question for anyone who can give me a good answer. I have a 750 Edelbrock on my 340 and it has been giving me problems lately where I cannot get it to idle consistantly. It sounds as if it is sucking air. Under acceleration the car runs great. Changed everything that has to do with vacuum , replaced the 2 caps on the front of the carb, new PVC, new Carb gasket, put on a new fuel regulator with 6 psi, checked the tubular fuel filter, etc.. and still will not idle consistantly. Since the carb is 14 years old and has never been rebuilt I took the carb to a very established engine builder and when he was tearing it down he noticed a few of the Metering Rods were broke. Now how do these break? The carb since I have had it has never been apart. This really confuses me...
 
a "few" of the metering rods broke? there are only two inside....i could only imagine to damage these when you remove the top of the carb with the rods inside....and misalign them during re-installation.

did you clean out the air bleeds on top of the carb?
 
Question for anyone who can give me a good answer. I have a 750 Edelbrock on my 340 and it has been giving me problems lately where I cannot get it to idle consistantly. It sounds as if it is sucking air. Under acceleration the car runs great. Changed everything that has to do with vacuum , replaced the 2 caps on the front of the carb, new PVC, new Carb gasket, put on a new fuel regulator with 6 psi, checked the tubular fuel filter, etc.. and still will not idle consistantly. Since the carb is 14 years old and has never been rebuilt I took the carb to a very established engine builder and when he was tearing it down he noticed a few of the Metering Rods were broke. Now how do these break? The carb since I have had it has never been apart. This really confuses me...
If everything is now correct with the carb, I would say you have a timing and/or ignition issue.
 
The problem is the troubleshooting strategy.
Start at the beginning.
1. Check fuel level.
2. Test what happens when the idle mixture screws are turned in and out. Does it run better with more or less fuel?
3. Look at the spark plugs - what are they showing ?
Go on from there.
 
The problem is the troubleshooting strategy.
Start at the beginning.
1. Check fuel level.
2. Test what happens when the idle mixture screws are turned in and out. Does it run better with more or less fuel?
3. Look at the spark plugs - what are they showing ?
Go on from there.
I have done all of the above Mattax..
 
and what's the level at?
what happened when you turned the screws in? How about out? how many turns?
what do the plugs look like?
 
a "few" of the metering rods broke? there are only two inside....i could only imagine to damage these when you remove the top of the carb with the rods inside....and misalign them during re-installation.

did you clean out the air bleeds on top of the carb?
No I did not..
 
and what's the level at?
what happened when you turned the screws in? How about out? how many turns?
what do the plugs look like?
I followed the Edelbrock instructions for adjusting the mixing screws. I actually had to increase the idle to 2k in order to do this, did not work out to well. As for the plugs I replaced all 8 even though they looked good.
 
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If you are at 2k you have probably uncovered the transition slot enough that it is not running on the idle mixture screws. So the step up rods, was the end broken off? If so it might be in the main well.
 
You can't adjust properly the idle mix with the throttles open.
You need to check the fuel level. You can set the floats dry, but checks IMO should be done wet whenever possible.
Looking at the plugs will give you an idea of how the burn went down and if its was excessively rich or lean.
If the mix screws aren't responsive, then that tells a lot.

The fact the engine speed had to be increased alone doesn't reveal if its timing or not, but certainly leaves the possibility open. Need the timing at least in the correct ballpark since it works hand in glove with the fuel mix and rpm. Mechanical timing around 2000 rpm should be around 24* BTC. On a stock distributor that will probably put it around 5 - 12* BTC at 1000 rpm. The 5* or less initial was for early smog and coupled with a lean idle (14.2:1). Since you're using an Eddy I'll assume thats not your situation. Initial of 10 - 15* would work best. (if its the stock emissions distributor, a put some more tension on the primary spring so it doesn't move out too fast)
 
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Cap and rotor? Run the car in the dark and look for bad plug wire. If its still doing it with new rods in it. Might not be the carb. Carbs get all the blame.
 
Metering rod carburetors are sensitive to vacuum signal. What camshaft are you running? Metering rods and large camshafts do not get along well at idle. The low vacuum signal causes the metering rods to jump around at idle and will cause an erratic idle situation. Can you give us some more details? Camshaft size, where your initial timing is and any other details will help.
 
I followed the Edelbrock instructions for adjusting the mixing screws. I actually had to increase the idle to 2k in order to do this, did not work out to well. As for the plugs I replaced all 8
Use a vacuum gauge to set the idle screws, do this at idle speed approx 750 rpm. Look for the procedure on line
 
Make sure the doggone secondaries close on the stop, and not on linkage interference.Back off the secondary throttle stop,and make sure that the two air valves both hit the throttle-bores simultaneously. Then reset the stop just enough to prevent sticking. Then make sure the flyweights in the D snap back onto their stops. After you get that done,Check/adjust your T-port sync,
AJ's guide to Transfer Port Synchronization

Hyup on the vacuum thing.
Finally,install a vacuum gauge on the manifold.With the engine idling, loosen one of the metering-rod cover-screws and flip the cover to the side a bit then retighten the screw,enough that it cannot come loose and fall into the engine. Then observe that the piston remains down, at idle.Then slow the engine rpm and continue to watch the piston as the vacuum drops. If/when the piston starts to dance,increase the idle speed about 50 rpm,and observe the vacuum reading. That will be your minimum vacuum required for the springs that are under the piston. If your engine requires more than 700/650 rpm to achieve that, then you will need different springs.
 
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Question for anyone who can give me a good answer. I have a 750 Edelbrock on my 340 and it has been giving me problems lately where I cannot get it to idle consistantly. It sounds as if it is sucking air. Under acceleration the car runs great. Changed everything that has to do with vacuum , replaced the 2 caps on the front of the carb, new PVC, new Carb gasket, put on a new fuel regulator with 6 psi, checked the tubular fuel filter, etc.. and still will not idle consistantly. Since the carb is 14 years old and has never been rebuilt I took the carb to a very established engine builder and when he was tearing it down he noticed a few of the Metering Rods were broke. Now how do these break? The carb since I have had it has never been apart. This really confuses me...

Here's something for you to check.
At idle look down the carb two front barrels and see if fuel is dripping from the two boosters I circled in red.
If you have ANY fuel dripping from these at idle it's because there are a small brass plug with a really small hole (air bleed) in the back side of these that gets plugged up with age. (most people miss this)
When the air bleed holes in the brass plugs get plugged up the idle vacuum is enough to pull fuel through them.
The holes let enough air in that at idle they don't pull fuel.

This would severely screw with your idle mixture and make the idle need to be higher to try and compensate for the extra fuel.

Edelbrock.jpg
 
All good advice here, but will add one little thing. I have seen the butterflies loosen and jam in the bore and not return to idle. Reaching down the venturi with a long screwdriver and tapping the butterflies while running will immediately settle this issue as it will center the butterflies and will return to idle. Worth a try.
 
If you are at 2k you have probably uncovered the transition slot enough that it is not running on the idle mixture screws. So the step up rods, was the end broken off? If so it might be in the main well.
Do not know if the ends were broken, my mechanic told me on the phone that the rods were broke off...
 
Here's something for you to check.
At idle look down the carb two front barrels and see if fuel is dripping from the two boosters I circled in red.
If you have ANY fuel dripping from these at idle it's because there are a small brass plug with a really small hole (air bleed) in the back side of these that gets plugged up with age. (most people miss this)
When the air bleed holes in the brass plugs get plugged up the idle vacuum is enough to pull fuel through them.
The holes let enough air in that at idle they don't pull fuel.

This would severely screw with your idle mixture and make the idle need to be higher to try and compensate for the extra fuel.

View attachment 1715226344
TrailBeast, I would but the carb is at my engine builder getting rebuilt. Thanks anyways for the tip
 
TrailBeast, I would but the carb is at my engine builder getting rebuilt. Thanks anyways for the tip

Check it when you get it back on the car, because like I said a LOT of people miss those being plugged up and can't figure out why the boosters are dripping fuel.
Usually they think it's a float level or needle/seat issue.
 
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