Just keeps wanting more fuel but why?

[Topcat]

A little backround on this engine. .063 bored 426 Hemi, 472 stroker kit, 10.25:1 CR. OEM carbs already jetted up. 
See camshaft picture specs below. It's a solid lifter cam with Johnson EDM lifters.

Intake manifold gaskets were just done.

Hemi's are notorious on intake manifold leaking.
I sprayed copper gasket stuff on with a light smear of high temp orange silicon around the ports.
So I know after cross torquing this manifold at least 5 times, I really doubt I have any manifold vacuum leaks.

I re jetted the carb up, at 2 sizes on the rear and front.
There are no adjustable idle screws on the front carb. OEM were pre set and epoxy'd in.

I just did another valve adjustment. They're tight. Gripping the feeler back and forth.
.019 intake. .015 exhaust done from the Mopar specs card call for on rotation.

Problem is: the engine won't get down lower than 1300 rpm on idle.

At a stoplight, I have to feather the gas pedal with my big toe to keep her from falling off and dying out.
It's like it's still starving for fuel on the idle circuit. Rear idle screws are almost all the way out.
When we put our hands over the tops of both carbs or add propane, the idle speed goes up 400-600 rpm est.

I don't want to get 2 more new carbs if I can get these to work.
Is it impossible or possible to have these factory carbs work with my set up?
I think it is possible but I need some help on what to do to make this all work!

See Youtube video below.



https://www.youtube.com/watch?v=nWUIhDTEaNM&feature=youtu.be

[cudabob496]

can't get idle lower than 1300?  Vacuum leak?

Cudaking71 recently said: "if you put your hand over the carb,does idle try to climb? If so its got a vacuum leak? Otherwise, should stall out."

[Topcat]

There's only 2 places left I could think of that might be a vacuum leak.

The power brake booster which was re built, or the head bolts that go up into the intake manifold.
I put torque grease on each of them using new ARP bolts.

[DocMel]

 TC.  I believe your carb(s) are the likely culprit, not vacuum, and that you are getting close to the prob.

Try not to get lost in the cam specs, the stroker work, etc.  It will be vey easy to wander about and away form the very basic issues that might be causing your symptoms.

But understand, with a stroked motor and your cam specs, setting idle down to 850-900 will be a little challenging;   But that not the issue here.  The "feathering" needed to pull out to me, is a classic sign of carb adjustment or fuel feed probs

It is good you went thru adj valves, etc.  You are ruling things out, but lets get back to basics

There is one huge sign to me in some of the descriptions that you mentioned that carb adj is the prob:

 Idle screws:  I am assuming you mean idle mixture screws.  You have a front carb that is non adjustable, and the rear seems to not make a dif, whether screwed in all the way or out.  This is huge signs of what might be causing the issue.  I have a book full of notes, and Ill get back with you asap on how to solve that prob

What will really confound this prob in the idle circuit with two, four barrel carbs, is if both carbs are not working correct down low (in idle, at stop when first pulling out), the one carb that might be right is only really feeding four cylinders, while the other four are ether starving for the correct idle mixture, hence give it a "little toe" to keep it from starving  off.  A carb could be way too lean or rich in the idle mixture 

If you are running a single plane intake, the prob will be even worse if you have a carb not right in the idle and transition circuit

Anyways, i have fought that prob and solved it, and Ill get with my notes and tell you what I had and get back asap.  You are so close in getting to the prob, I feel for you



ngs to me

[Topcat]

TC.  I believe your carb(s) are the likely culprit, not vacuum, and that you are getting close to the prob.

There is one huge sign to me in some of the descriptions that you mentioned that carb adj is the prob:

 Idle screws:  I am assuming you mean idle mixture screws.  You have a front carb that is non adjustable, and the rear seems to not make a dif, whether screwed in all the way or out.  This is huge signs of what might be causing the issue.  I have a book full of notes, and Ill get back with you asap on how to solve that prob

What will really confound this prob in the idle circuit with two, four barrel carbs, is if both carbs are not working correct down low (in idle, at stop when first pulling out), the one carb that might be right is only really feeding four cylinders, while the other four are ether starving for the correct idle mixture, hence give it a "little toe" to keep it from starving  off.  A carb could be way too lean or rich in the idle mixture 



ngs to me

This is exactamundo! what you said and what I believe is the problem.

Yeah! I want my cake and ice cream!

A factory looking stroked Hemi.
Can it be done is where I'm heading!

[DocMel]

Check fuel pressure first.  If this isn't right, you will chase your tail.  Remember, you have small margin of error here.  5.5 pds is just about right.  5 might be too low, 6 and higher, too high 

For a fairly radical camshaft it may require an excessive amount of throttle opening for idle and, or you might have have low idle vacuum levels. Either condition can lead to poor levels of adjustability and erratic idles. Measure the manifold vacuum at idle. It needs to be at least 7" Hg
   
Another possible fix is to run as much spark advance as possible at idle. If the distributor is fitted with a vacuum advance unit, connect it directly to manifold vacuum. If you are not able to employ vacuum advance for some reason, then the mechanical curve should have a low limit, which will allow you to use plenty of initial spark advance.

Ok, there is another issue about idle mix screws not making any changes in idle quality whether all the way in or out. This WILL cause the need for "toeing at idle and pull out":    I need to look for that in my notes and remember it was a simple fix. I just cant remember what it is

Again, I am whole heartedly thinking your idle circuit/mixture is the culprit

Think idle mixture again.  In dual carbs, if one is good, the other isn't, you will be basically be feeding only half the engine the correct idle mixture, and the other half could be too lean or too rich at idle, and this prob will be tripled if you are running a single plane intake

im wondering why the front carb idle mix crew is sealed.  Is that the way they should come?  Up front, in my mind, you should be able to adjust the idle mixture.  I though sealed mix screws were an emissions thing 

Last: Are these carbs new or rebuilt?

 

[Topcat]

These were re built OEM carbs from Scott Harms at Harms Auto.
Then were re jetted them with a carter strip kit.

ML 4745S and ML 4742S

[Topcat]

im wondering why the front carb idle mix crew is sealed.  Is that the way they should come?  Up front, in my mind, you should be able to adjust the idle mixture.  I though sealed mix screws were an emissions thing 

Last: Are these carbs new or rebuilt?

All factory OEM 70-71 Hemi carbs have staked, sealed front idle mixture screws that are no adjustable.

My carbs are 1970 Modified for 71' made the 11th or 12th month of 1970. Very rare.

[1 Wild R/T]

The RPM's rising when you take away the air is a clear indication of a lean mixture but the engine dieing may be another issue... I don't know what ignition your running or if the curve has been worked but I've seen plenty of times when the timing comes in at so low an rpm that when you idle down timing is falling out near the idle speed... If that happens it can be a vicious cycle, lose 2-3 degrees of timing & the rpm's fall 100-200 rpm.. Lose that 100-200 rpm & more timing falls out... Your heading straight to an inevitable stall...   For testing it might be good to use a small zip tie to lock out mechanical advance...

[Topcat]

I'm at 18 degrees BTDC right now. Was at 16 prior.

[1 Wild R/T]

I'm not talking base timing, I'm asking about what the mechanical advance is doing at/just above idle...

[rUNCHARGER]

Those carbs will work great if they're in good shape. 18 degrees initial should work well. In my area I have to jet up about 5 sizes at every position to get Hemi carbs to run right on the fuel we are stuck with. You will most likely have to change the step up springs with that camshaft.
I would check for a vacuum leak somewhere as well to be sure.

Sheldon

[1 Wild R/T]

Just read you advance curve thread... MP Electronic... I about guaranty your stalling is do to the timing falling out at the wrong time...  Zip tie the weights, work on the carb till your happy with the idle then deal with the advance..

[Chryco Psycho]

it may come down to drilling holes in the throttle plates so you can get the throttle plates closed down so the idle transfer slots are covered properly & idle mix becomes responsive again . Not sure you want to do this to rare factory carbs though . you might want to run it with cheaper carbs that cannot be seen under the shaker hood anyway . Have you swapped springs under the metering rods to make sure they are staying down at idle also

[Topcat]

I'll try the springs and concentrate on ignition next.