Hesitation / Stumbling, runs rich at idle

[Dan the man]

I'm hoping that you guys can help us out here. A friend of mine has a 1975 Vega with a 4.3 V/6 in it. It's stock except for a 4 barrel, headers,and hei ignition. He put a edelbrock 500 cfm carburetor on it and it has a hesitation and stumbles when he tries to accelerate,once he's past that it runs strong.
He said he can smell gas in the exhaust and the plugs show that it's running rich, he tried different jets, float level adjustment, accelerator pump and adjustment it too, choke is working ( it's electric ). He tried setting the idle from 500-750 rpm's, he checked the idle mixture and nothing helps. So he went with a Holley 600, same problem so he did the same things as he did to the edelbrock and no difference, the hesitation, stumble are still there as is the rich running condition. He checked the fuel pressure and it's 5 pounds. It doesn't make sense why it runs the same way with 2 different carbs. The intake is a edelbrock dual plane with a drop down plenum, I don't know if that makes any difference. The timing is good and the vacuum advance is hooked up and working properly. Any help, suggestions, ideas would be greatly appreciated. It has us both puzzled, especially since it runs the same no matter which carburetor he uses. Thanks

 

[George Jets]

What coil is he running with that HEI? In the cap e-core coil GM?

Anyway you need to run a high output E-core coil, and open up the spark plug gap to .050 ths.

Being that is a powerful fast ignition, you need to back down (retard) the timming 4° from 12° BTDC to 8° to put the "Fireball" in the best position to put the most rotational force to the crankshaft.

Plugs will burn clean and same with the tailpipe > clean, not black. A more efficient burn.


☆☆☆☆☆

 

[Oldmanmopar]

Take the distributor cap off and turn the engine back and forth while watching the rotor in the distributor. How much play does the chain have. Seen this more then once. A stretched chain can cause a hesitation.

One other thing that causes this is if the primary transfer slot is not square and you are already into the power valve system. Square the primaries and idle off the secondaries . If you have no secondary idle adjustment drill holes in the venturis to achieve proper idle while primaries are square

 

[junkyardhero]

Anyway you need to run a high output E-core coil...

Being that is a powerful fast ignition, you need to back down (retard) the timming 4° from 12° BTDC to 8° to put the "Fireball" in the best position to put the most rotational force to the crankshaft.

source?

 

[RustyRatRod]

Put a LS in it.

 

[junkyardhero]

Put a LS in it.

pfft! that's so 2015. it's all about that 3800 super charged mo-tree!

 

[Bewy]

E core coil is more powerful than a canister coil. Below shoes why....
Just make sure with the E core coil that is designed for inductive ign [ HEI & others ]. A dedicated CD E core coil is different.

 

[Oldmanmopar]

Checking the coil for good spark in the shop. Attach a long copper wire from the coil to a tool . Have a smart *** youngster in the shop hold the tool for you.

With the key turned on rotate the distributor. Watching his reaction will confirm the amount of output. Does he grab is elbow or his shoulder post the testing proceedure?

 

[Dan the man]

Thanks everyone for all the suggestions. Even adjusting the transfer slots didn't help. My question is would the drop plenum design have any affect on the hesitation and stumbling issues along with it running rich? I looked up those manifolds and I found that you have to run at least a 1" open spacer in order to be able to tune the carburetor correctly, this true?The article said something to do with the carburetor signal.
I don't have a lot of knowledge on carburetors. Have any of you have or had experiences with a drop plenum dual plane intake? Once the engine gets passed the hesitation it runs great. Hopefully someone on here has had a manifold with a drop plenum. Apparently edelbrock doesn't have them for the sbm at least not from what I could find. Thanks guys

 

[TT5.9mag]

Being that is a powerful fast ignition, you need to back down (retard) the timming 4° from 12° BTDC to 8° to put the "Fireball" in the best position to put the most rotational force to the crankshaft.

Absolutely NOPE. This advice should not be followed.

 

[TT5.9mag]

Thanks everyone for all the suggestions. Even adjusting the transfer slots didn't help. My question is would the drop plenum design have any affect on the hesitation and stumbling issues along with it running rich? I looked up those manifolds and I found that you have to run at least a 1" open spacer in order to be able to tune the carburetor correctly, this true?The article said something to do with the carburetor signal.
I don't have a lot of knowledge on carburetors. Have any of you have or had experiences with a drop plenum dual plane intake? Once the engine gets passed the hesitation it runs great. Hopefully someone on here has had a manifold with a drop plenum. Apparently edelbrock doesn't have them for the sbm at least not from what I could find. Thanks guys

You guys need to open a book and learn how to tune the idle and transition circuits of whatever carb you’re going to use. Hint; Jets and power valves are not it. Checking the fuel pressure was a good thing, now go set the float levels, make sure the needles seat and stop fuel flow, then TUNE the thing. Hint 2, the accelerator pump/squirter needs to be working well and tuned properly as well.


I said squirter.

 

[Dan the man]

You guys need to open a book and learn how to tune the idle and transition circuits of whatever carb you’re going to use. Hint; Jets and power valves are not it. Checking the fuel pressure was a good thing, now go set the float levels, make sure the needles seat and stop fuel flow, then TUNE the thing. Hint 2, the accelerator pump/squirter needs to be working well and tuned properly as well.


I said squirter.

He said that the float levels are good and the needle seats are not stuck. I'm going to have him double check what he's already done. Both carburetors were new right out of the box and the car did the exact same thing with both carbs..

 

[TT5.9mag]

Both carburetors were new right out of the box and the car did the exact same thing with both carbs..

That says it all. I don’t care what anyone says, there is NO “bolt on and go” carburetor. They all need some level of tuning.

 

[TT5.9mag]

Edlebrock carbs have a very specific float level adjustment and are (almost) never correct out of the box. Holleys have different float levels depending on the type of sight plug/glass the bowls have and are never correct out of the box. Saying float levels are “good” or timing is “good” doesn’t help anyone help you. Specifics are important. For example, if it has 2 degrees of idle timing we can almost guarantee the transfer slots are overly exposed and causing a problem. The relationship between carb and ignition is a big one.

 

[junkyardhero]

new out of the box ≠ it's any good. trust but verify... always.

also, wtf is a "drop plenum" manifold? this sounds like some **** you just made up.

 

[Dan the man]

That says it all. I don’t care what anyone says, there is NO “bolt on and go” carburetor. They all need some level of tuning.
[/QUOTE
That's what I thought. I don't have a lot of experience with carburetors that's why I wanted to ask you guys

 

[Dan the man]

new out of the box ≠ it's any good. trust but verify... always.

also, wtf is a "drop plenum" manifold? this sounds like some **** you just made up.

I don't know much about it, all he said was it's a edelbrock performer intake manifold with a drop plenum, so I looked it up and sure enough that's what it says it is.

 

[Dan the man]

I don't know anything about holley carburetors, Randy claimed that since the float level looks good through the sight glass that the float level is fine and that means the needle and seat are not sticking because it accelerates good once it's passed the hesitation. Supposedly he's changed the jets, adjusted the accelerator pump and the squirters are working correctly, myself I don't know how to check those. Float level is good, timing is right but he still has the exact same problem with both carburetors, the one carburetor is a edelbrock 500 and the other is a holley 600. From what I've read on the intake he's using is messing up the carburetor signal and he said no way.

 

[junkyardhero]

I don't know much about it, all he said was it's a edelbrock performer intake manifold with a drop plenum, so I looked it up and sure enough that's what it says it is.

source?

 

[Dan the man]

source?

I don't know what to believe anymore, I went to the search bar on my phone and I found information on it and I went back a few minutes ago and it said that edelbrock doesn't make a drop plenum intake manifold

 

[Dan the man]

source?

I give up, he thinks that he knows everything and every suggestion I make is wrong. Now he claims that the idle doesn't have anything to do with the transfer slots.

 

[fishmens67]

Upgrade to a 350.

 

[junkyardhero]

I don't know what to believe anymore, I went to the search bar on my phone and I found information on it and I went back a few minutes ago and it said that edelbrock doesn't make a drop plenum intake manifold

muh-huh

 

[Dan the man]

Upgrade to a 350.

He's already had a small block vega, he wanted to try a V6

 

[George Jets]

☆☆☆☆☆