Lean pop off idle?

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Craig Burriss

Craig Burriss

FABO Gold Member
FABO Gold Member
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Hey guys, I’ve been trying to get my fresh built 440 RamCharger running right, and haven’t had much luck. I haven’t been able to spend much time with it lately, so I’m hoping someone here can point me in the right direction. I set the base timing at 16btdc, (haven’t checked total timing yet. I know I should). At first I bolted the carb on, and was able to break-in the engine. Whenever I try to accelerate at all, it falls on its face and pops out of the carb, sometimes stalling the engine.

Here’s some details.
440 big block/manual transmission
Holley 770 street avenger (single pumper)
Aluminum dual plane intake
452 iron heads
Forged aluminum pistons (9:1 compression)
RV cam (see pic for specs)
Mopar electronic vacuum advance distributor
Mopar blue ignition box
440 source 10mm plug wires
MSD Blaster coil
Autolite #85 plugs
Full length headers with 1 3/4 primaries
Edelbrock mechanical fuel pump
New 3/8 fuel line/filter all the way to the clean tank
87 octane fuel.

I followed Holley’s instructions on setting the accelerator pump, so it starts pumping fuel as soon as the throttle is touched. I’m confused on the curb idle screw, because some say adjust it until you can barely see the transfer slots, and some say you shouldn’t be able to see them at all. I’m also confused on the sizing of the accelerator pump nozzle and diagram sizing, as some say for heavier vehicles, you need a larger one, and then some say a smaller one.
I can see fuel through the little sight glass on the sides of the bowls, it’s towards the bottom of the window.
I’ve tried tuning the idle air screws with a vacuum gauge, but that didn’t seem to help, I was able to get about 16Hg at idle. I’ve checked for vacuum leaks and don’t believe I have any.
Any input is appreciated.
Thanks, Craig.
67B567CE-D4B6-4EA8-99F5-3C17CCC11CF1.jpeg
 
What is a Mopar blue ignition box? The only blue things I have seen is a voltage regulator. Whose distributor is it? Did you check the air gap? I have seen them be way off out of the box.
 
66Valiant528 said:
What is a Mopar blue ignition box? The only blue things I have seen is a voltage regulator. Whose distributor is it? Did you check the air gap? I have seen them be way off out of the box.
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It’s the factory ignition box... they have blue ones, orange ones, and black ones.
 
I had this problem with my Duster and I think I solved it.

First I moved up 3 sizes on the squirter 32 to 35) and still had the problem. Then I found a green pump cam in my spare parts and replaced the pink one in the carb with it and that finally got rid of the off idle hesitation. I'm sure there's a more scientific way to figure out what cam you need, but I'll be darned if I could find it online. I found people saying change to red, change to orange, change to white, but I think it's a matter of getting rid of the symptom and moving on unless you've got an air/fuel ratio system installed.

I might be able to go back to a smaller squirter but the carb needs to come off to change that because the choke's in the way and I'd have to take it off after I dropped parts into the carb anyway. So I haven't tried that yet.
 
Disconnect vacuum advance and cap it at the carb. If the off idle stumble gets better, the advance can is leaking. This assumes you are connecting to the timed vacuum port on the side of the metering block.
 
  • Check that all of your plug wires are popped on all the way on the plugs.
 
What rear end gear ratio and tire diameter?
If the heat crossover in the intake open or plugged?

I would swap on a different coil and try it. Doesn’t take long and lots of probs with the cheapie MSD unit.
 
Assuming it's a 80770 mdl, it has a factory installed #31 squiter. Plenty for a dual plane intake. The primary jet is #70, "might" be a little lean for your application with that size carb. And the PV is a 6.5. No reason you couldn't step that up to a 10.5 with that cam & vacuum.

As far as idle mixture settings on all the Holley's i have had, (many), turn in to stumble, back out to smooth and go 1/8th turn out. The vacuum will be what it will be.

All that said, i'm not yet convinced it's a carb problem. Something haywire in the timing could very well be it. Just hope it ignition and not cam. :)
 
413 said:
What rear end gear ratio and tire diameter?
If the heat crossover in the intake open or plugged?

I would swap on a different coil and try it. Doesn’t take long and lots of probs with the cheapie MSD unit.
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Currently has 3.23 with 33s.
Heat crossover is unblocked.
 
Yeah that's not a small tuning problem, if you have another working carb perhaps replace it and see what happens, you could use the same technique on your ignition box. It's just a good way to eliminate big chunks of the equation instead of being all over the place.
 
This could also be retarded timing. Have you checked it? Low comp engines need MORE timing, so I would check/adjust timing to about 15* BTDC. Also plugs too cold will cause the problem, should be a '5' heat range in NGK.
 
Too easy;
the advertised duration of that cam is way too big, for what you are trying to do. At idle your cylinder-pressure is gonna be really low. That engine is gonna want a lotta Idle-timing.
And your transfer slots need to be exposed to a lil taller than wide. Forget what anyone told you. You will know that the transfers are about right, when you can run the mixture screws in or near the center of their range. If the idle-speed is too fast, retard the timing.
But this combination of tall Transfer slots and mega Idle-Timing is gonna make the Idle-speed too high. I can see this combo may require the Vacuum-Advance can be connected to manifold vacuum, and the Base timing set with it engaged.
Forget using the manifold-vacuum for tuning the idle.

But here is the really big deal; Your accelerator pump has to pump fuel at the slightest throttle movement, and that means at a gentle tip-in. To do that, fuel has to be in the pumpwell, right to the top, and the lil check-valve has to be holding it back, so that when the fuel comes thru the shooters, it is blasting off the boosters; No dribbling allowed; you need a fine spray.

I highly recommend a compression test.
I don't like that cam one bit.
 
You can rule out timing very simply by bumping initial up to "about" 20 degrees. Your compression is very likely NOT 9:1. Those forged pistons are probably stock replacements and compression is much more likely in the 8.5 range, which means the engine will want about all the initial timing you can give it. A simple test. Start the engine and let it warm up. Loosen the distributor and slowly pull in timing until it stops idling up. Check the initial. This is about where the engine wants to be. That camshaft has been ground by nearly every cam manufacturer in the world. It's a decent grind, there's nothing wrong with it. Are there better grinds? Sure, there are better grinds no matter which one you choose, but you can make it run very well by following some simple tuning advice. I wish you were a little more local, I would give you a hand and probably have it running very good. Try the timing first. It's the easiest to rule out and if it doesn't make a difference, you can put it right back where it was.
 
RustyRatRod said:
You can rule out timing very simply by bumping initial up to "about" 20 degrees. Your compression is very likely NOT 9:1. Those forged pistons are probably stock replacements and compression is much more likely in the 8.5 range, which means the engine will want about all the initial timing you can give it. A simple test. Start the engine and let it warm up. Loosen the distributor and slowly pull in timing until it stops idling up. Check the initial. This is about where the engine wants to be. That camshaft has been ground by nearly every cam manufacturer in the world. It's a decent grind, there's nothing wrong with it. Are there better grinds? Sure, there are better grinds no matter which one you choose, but you can make it run very well by following some simple tuning advice. I wish you were a little more local, I would give you a hand and probably have it running very good. Try the timing first. It's the easiest to rule out and if it doesn't make a difference, you can put it right back where it was.
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Yep, or unplug a vacuum gauge and replace the vac cap, in my case...
 
Ironracer said:
Yep, or unplug a vacuum gauge and replace the vac cap, in my case...
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It's just a no brainer to try all the "free stuff" first. I swear, some of these guys in here would have him swappin engine parts just cause "THEY" don't like um. I got news. People have been running that exact same grind, and the one right below it (204 and 214 @.050) for DECADES with good success on the street. Yes, admittedly, they are dated grinds, but they WORK. Fine for everyday street cruising. Easy on the valve train and can make power when the engine is tuned around them.
 
RustyRatRod said:
You can rule out timing very simply by bumping initial up to "about" 20 degrees. Your compression is very likely NOT 9:1. Those forged pistons are probably stock replacements and compression is much more likely in the 8.5 range, which means the engine will want about all the initial timing you can give it. A simple test. Start the engine and let it warm up. Loosen the distributor and slowly pull in timing until it stops idling up. Check the initial. This is about where the engine wants to be. That camshaft has been ground by nearly every cam manufacturer in the world. It's a decent grind, there's nothing wrong with it. Are there better grinds? Sure, there are better grinds no matter which one you choose, but you can make it run very well by following some simple tuning advice. I wish you were a little more local, I would give you a hand and probably have it running very good. Try the timing first. It's the easiest to rule out and if it doesn't make a difference, you can put it right back where it was.
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On the car I mentioned above I added timing up to 40* before it stopped speeding up. It's set at 22* now and it's limited to 34* max. The car has an Edelbrock Torker intake and a 1" spacer with 10" or vacuum. Big plenum area, low vacuum to start, no vacuum at all once you crack the throttle, increase the squirter by 3 and tune the cam to provide more fuel. The carb book I used (by Dave Emanuel) has pretty much those exact words in it.

I fell into the trap of thinking I was going to end up pulling the motor apart to check the cam and/or replace it until I calmed down and worked the simple stuff.
 
I didn't say a single word about whether that cam is; good, bad, or whatever. Nor did I suggest to replace it. All I said was;
AJ/FormS said:
I don't like that cam one bit.
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and the reason I said that is because of exactly what it is doing in this particular combo, and what it will continue to do.

BTW;
the Wallace Calculator predicts;
at a true 9/1 Scr, cranking cylinder pressure is likely to be ~130psi, which is pretty Low Compression.
At 8.5 this drops to ~120psi which is nearer to Miserably Low.
 
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AJ/FormS said:
I didn't say a single word about whether that cam is; good, bad, or whatever. Nor did I suggest to replace it. All I said was;

and the reason I said that is because of exactly what it is doing in this particular combo, and what it will continue to do.

BTW;
the Wallace Calculator predicts;
at a true 9/1 Scr, cranking cylinder pressure is likely to be ~130psi, which is pretty Low Compression.
At 8.5 this drops to ~120psi which is nearer to Miserably Low.
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I don't remember mentioning your name, but as they say a hit dog hollers.Yes, it may be "miserably low" as you say, but can still be tuned to run surprisingly well. Just because you rely on slide rules and calculators and have no real world experience is not "my fault". I'm sure in your world, you pick all the greatest parts to work together better than in anyone else's world, but I'm not impressed. One way of thinking has never fit all. Get over yourself.
 
Uncle Bob said:
On the car I mentioned above I added timing up to 40* before it stopped speeding up. It's set at 22* now and it's limited to 34* max. The car has an Edelbrock Torker intake and a 1" spacer with 10" or vacuum. Big plenum area, low vacuum to start, no vacuum at all once you crack the throttle, increase the squirter by 3 and tune the cam to provide more fuel. The carb book I used (by Dave Emanuel) has pretty much those exact words in it.

I fell into the trap of thinking I was going to end up pulling the motor apart to check the cam and/or replace it until I calmed down and worked the simple stuff.
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Sometimes you see that if the cranking pressure is really low. Then, you kinda have to play it by ear. I've seen some take 22 degrees initial.....but that's probably about "as far" as I'd go, UNLESS I decided to lock out the timing, which I've never done. IMO, that's a step best left for race only, or almost race only engines.
 
RustyRatRod said:
Sometimes you see that if the cranking pressure is really low. Then, you kinda have to play it by ear. I've seen some take 22 degrees initial.....but that's probably about "as far" as I'd go, UNLESS I decided to lock out the timing, which I've never done. IMO, that's a step best left for race only, or almost race only engines.
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Yeah, it does have low cranking pressure. When I first got it there was a Mopar tach drive distributor in it set up to go to max advance as soon as the car started.
 
Uncle Bob said:
Yeah, it does have low cranking pressure. When I first got it there was a Mopar tach drive distributor in it set up to go to max advance as soon as the car started.
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Jim and Cody Laroy are award winning engine builders. IQ52 is Jim's screen name here. He has posted in detail more than one build with very low static compression that makes a lot of power. One was a 7.35:1 engine. That's why I always tell people to try to tune "what they have" first, because without fail, working with what's already there is the most budget friendly path.
 
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