383 Wont Idle with new to me 800cfm DP. Idles and runs ok with Edelbrock/AFB

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I said 7 to 8 inches


First off, again, you set power valve opening at just under CRUISE vacuum. Idle vacuum means nothing. Get that idea out of your mind, and let no one tell you otherwise. Mark Whitener, who is about as good a carb guy as you can find, posted a video proving that idle vacuum has nothing to do with power valve opening.

Second, you do not have 11:1 if you have zero deck. It's just about impossible. If you know the part number of the piston you used, you can look it up but I'd bet you need to be .035-.040 out of the deck to get that CR unless you milled the piss out of the heads.

That means you have other issues. That .509 cam on a 112 LSA would be a worthless detonation maker. The 108 is a much better cam.

Even at 11:1, with iron heads and pump gas you should be able to get 38 total on it. I'm running 11:1 (an actual measured 11:1 and to do that I had to mill the heads .040 and stick the piston out .045) on iron heads and pump gas and I run 36 total with zero detonation.

So it can be done IF you plan for it. And you tune for it. For what I wanted I needed 255 at .050 and anything less than 11:1 it would have been a pig. Of course you can't roll along in high gear at 12 MPH and smash the throttle. But who does stupid **** like that? Only fools that think it's cool. Other than that, there is no reason why what you have won't run with full timing on pump gas.

So start over, verify the cam and the cam timing and then tune from there.

Notice I'm ignoring the idle issue you're having. That's a seperate issue. I'm talking about not getting full timing with what you have.
 
Ok update on the carburetor. I went through the Holley again and didn’t really find anything off. Main jets are 70 in the front and 85 in the back. Power valve is a 6.5. I installed a 1 inch carb spacer for 3 reasons 1 I wanted to experiment with more plenum volume, 2 I needed to gain some clearance from the choke well on the intake because it was causing the secondary linkage to not open more than half way, and 3 I was buying. New carb gaskets anyway so used this a way to get them.
I did flip the secondary throttle stop screw so it can be accessed from the top (great tip). Reinstalled carb and started vehicle. Same exact issue as before. Only idle at 1800 rpm. Lowering idle while adjusting mixture screw had no effect. I then turned the secondary throttle screw out 1 turn and restarted engine. I was now able to lower idle down to normal idle speed of 800. I tried adjusting idle mixture. Idle mixture screws have no effect. I can turn them all the way in or all the way out. engine still sits and idle sand wont stall. I am thinking it is getting fuel from either a leaking or incorrect for my combo power valve. I feel like me adjusting the secondary throttle stop is a bandaid covering up another issue. On a good note the car runs really well power wise with the 800 on it.
Well. Good Luck. Can't speculate further about whether its a bandaid or not. Might be be, might not be.
Pretty much covered how to proceed in posts 11 & 12.
 
I'll start out by name-dropping Vic Edelbrock here LOL that way I'll get some credibility and then you can listen to the rest of the crap. I just pulled a crappy one barrel Rochester off of a 78 and the float was sunk. The thing wouldn't Idol for crap. put help me with tuning my carburetors and I know you don't want to go into this on a tight budget but $150 wideband O2 sensor can tell you a lot about how things are burning. I'm the last one to cyber spend money but this is a great tuning tool for the unlearned...
 
I'll start out by name-dropping Vic Edelbrock here LOL that way I'll get some credibility and then you can listen to the rest of the crap. I just pulled a crappy one barrel Rochester off of a 78 and the float was sunk. The thing wouldn't Idol for crap. put help me with tuning my carburetors and I know you don't want to go into this on a tight budget but $150 wideband O2 sensor can tell you a lot about how things are burning. I'm the last one to cyber spend money but this is a great tuning tool for the unlearned...
Maybe. But you didn't need a WBO2 to tell you that the float was shot, did ya. :poke:
Please don't tell me you did!
:p
 
Well. Good Luck. Can't speculate further about whether its a bandaid or not. Might be be, might not be.
Pretty much covered how to proceed in posts 11 & 12.
I am still working on it. I do appreciate the advice. I did follow your advice from those posts. I was unable to get it to run though. After I slightly opened the secondaries I was able to idle it down. That being said even with the primary throttle plates completely closed I still have no effect from mixture screws.
 
First off, again, you set power valve opening at just under CRUISE vacuum. Idle vacuum means nothing. Get that idea out of your mind, and let no one tell you otherwise. Mark Whitener, who is about as good a carb guy as you can find, posted a video proving that idle vacuum has nothing to do with power valve opening.

Second, you do not have 11:1 if you have zero deck. It's just about impossible. If you know the part number of the piston you used, you can look it up but I'd bet you need to be .035-.040 out of the deck to get that CR unless you milled the piss out of the heads.

That means you have other issues. That .509 cam on a 112 LSA would be a worthless detonation maker. The 108 is a much better cam.

Even at 11:1, with iron heads and pump gas you should be able to get 38 total on it. I'm running 11:1 (an actual measured 11:1 and to do that I had to mill the heads .040 and stick the piston out .045) on iron heads and pump gas and I run 36 total with zero detonation.

So it can be done IF you plan for it. And you tune for it. For what I wanted I needed 255 at .050 and anything less than 11:1 it would have been a pig. Of course you can't roll along in high gear at 12 MPH and smash the throttle. But who does stupid **** like that? Only fools that think it's cool. Other than that, there is no reason why what you have won't run with full timing on pump gas.

So start over, verify the cam and the cam timing and then tune from there.

Notice I'm ignoring the idle issue you're having. That's a seperate issue. I'm talking about not getting full timing with what you have.
Unfortunately I do have a true measured 11.5 to 1. I guess I should have specified that the flat part of the piston was at zero. There is a substantial dome on the piston with a notch for the spark plug.
 
Then what will help to start to narrow the issues:
Carb list number and revision.
The amount the transfer slots are now visible below the throttles.
Fuel level.

When you get a chance timing at 800 and some higher rpms.
However, my inclination here is still to return the carb and start with used old school one.
I think its going to need some reworking and that means you'll need to do it, along with a bunch of learning.
There's some weird carbs that are just bad to start with. No reason to knock your head against the wall with those.

and psst. A power valve leak is one thing, but an open PV is completely different.
The power valve opening just allows more fuel into the main well. The idle jet is downstream. There's a big hole (the main jet) and a small hole after that (the idle feed restriction). It doesn't matter if the big hole is even bigger. You can take the main jets out or open the PV and it shouldn't effect idle. At least when things are set up properly and sized right. It can make some effect when things are off - like the main jets are small and the IFRs are large. Even then, not a major effect like your dealing with.
 
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Maybe. But you didn't need a WBO2 to tell you that the float was shot, did ya. :poke:
Please don't tell me you did!
:p
IMG_20190506_142635.jpg

The one barrel was a customer's today, the O2 sensors to help me fiddle with my dual quads- Edelbrock's if you will...
 
Then what will help to start to narrow the issues.
Carb list number and revision.
The amount the transfer slots are now visible below the throttles.
Fuel level.

When you get a chance timing at 800 and some higher rpms.
However, my inclination here is still to return the carb and start with used old school one.
I think its going to need some reworking and that means you'll need to do it, along with a bunch of learning.
There's some weird carbs that are just bad to start with. No reason to knock your head against the wall with those.

and psst. A power valve leak is one thing, but an open PV is completely different.
The power valve opening just allows more fuel into the main well. The idle jet is downstream. There's a big hole (the main jet) and a small hole after that (the idle feed restriction). It doesn't matter if the big hole is even bigger. You can take the main jets out or open the PV and it shouldn't effect idle. At least when things are set up properly and sized right. It can make some effect when things are off - like the main jets are small and the IFRs are large. Even then, not a major effect like your dealing with.
I totally agree if you're not into this carburetor anyting and can take it back that sometimes they just are off for whatever reason. I thought myself like I said I could get that Edelbrock to work and I thought my friend was just another Chevy car that couldn't adjust a carburetor. I cleaned it like a shiny penny once again and put a brand new carburetor can a brand new Jets new metering rods in the correct Springs all stock one and a half turns out and it still would not idle no matter what I did.
also I think there's a reason your friend gave you this carburetor with no strings attached as quite possibly it had the same problem before and didn't want you to come pissed off because you spent a bunch of money. And hey if it worked you'd be happy to give him the money. No lost on either part...
 
If opening the back barrels helped the idle, then I think you are spot on. You are band aiding a problem with your primaries. The transfer slots are important and yes, the secondaries are used in idling, but little. Should be mostly the primaries. Now I say one of 2 things, your primaries are not delivering any fuel till part way open, and that is why it only idled at 1800 rpms, or the primaries are delivering too much fuel, causing it to die unless opened up to 1800 rpms. This is very easy to tell, and the flooding would girgle it to a die. No fuel will be just that - like running out of gas. This would explain the idle jets not working, no fuel to work with... LOL
 
No, it won't. Please stop repeating that error.

If you read post #1 he said 1800 RPM was his Idle speed, That is high enough to pull fuel from the boosters and if the vacuum is low it will pull extra fuel from the PV if the PV is under that vacuum.
 
Unfortunately I do have a true measured 11.5 to 1. I guess I should have specified that the flat part of the piston was at zero. There is a substantial dome on the piston with a notch for the spark plug.


Wish you had the piston part number. Did you actually down fill the cylinder, CC the chamber and do the math? Because I've never, ever seen a piston for a Chrysler that was designed for an open chamber head that actually had the advertised CR with a zero deck. I'm not talking about the dome. I'm saying the flat has to be out of the bore usually .040 or so to get anywhere near the CR you are talking about. Zero deck means little when you have a recess in the head that is anywhere from .080-.100 or more depending on how much was milled off. I detest online CR calculators. If you've ever built an engine with a CR limit you wouldn't trust them either. Because the piston guys lie, the dome volumes are always what they say, the valve pockets are always deep enough to run a net .800 lift and crap like that.

On top of that, if you are zero deck, you have at least .060 recess (maybe more) plus the gasket. You'd have been better off with the piston out of the hole (like Chrysler has said to do from day 1) to get the quench closer to .040 including the gasket and mill the dome down to get the CR where you want it.

Back to the carb. Throttle blades are cheap. Drill a .0625 hole in each primary butterfly and see if you can get the idle circuit to work. Evidently, the blades are open too far and that's why the screws don't work. If that helps, go bigger. I've had to go as big as .187 to get the butterflies shut far enough to get back on the idle circuit. Until you get the butterflies shut so the idle circuit working you're just banging your head against the wall.

Once you get the idle circuit functioning, you can move on to other stuff.
 
If you read post #1 he said 1800 RPM was his Idle speed, That is high enough to pull fuel from the boosters and if the vacuum is low it will pull extra fuel from the PV if the PV is under that vacuum.


No, I'm referring to posts 8 and 23. You do not set power valve opening based on idle vacuum. That is just dead wrong and it needs to stop being promulgated. You set PV opening based on cruise vacuum. I run a 10.5 PV and I have about 9 inches of vacuum at idle. The power valve is not open, and it not passing fuel. It can't, unless the diaphragm is ruptured and then it won't matter what the vacuum rating is.
 
If you read post #1 he said 1800 RPM was his Idle speed, That is high enough to pull fuel from the boosters and if the vacuum is low it will pull extra fuel from the PV if the PV is under that vacuum.
Actually very unlikely there was enough velocity at 1800 rpm to initiate the boosters in that carb/engine combo - especially out of gear.
And if it did, the vacuum would be relatively high because there is no load and very little throttle is needed.
 
If you start "drilling holes" in this highly suspect carb you'll own it...
I suggest NOT...
 
If you start "drilling holes" in this highly suspect carb you'll own it...
I suggest NOT...


That's why I said throttle blades are cheap. He can replace them easily and cheap if he doesn't want the carb. He's out a few bucks and some time. That's most likely one of the OP issues. He can't get enough air through the carb without opening the blades so far it's off the idle circuit.

Or, I'm misunderstanding what he's saying. Which is possible. Any time you have to open the blades up to make them run that gets the blade past the transfer slot you need to drill the blades. Newer Holleys come with a built in adjustable bleed so you don't need that.

Between cars and two strokes I've been trying to get guys to shut the throttle to make them idle. Funny thing is, all the 2T heroes and gurus used to say you can't make them idle and be fast. Then came the "modern" 4T and those pigs have to idle. So yes, any IC engine should idle. On its idle circuit.
 
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That's why I said throttle blades are cheap. He can replace them easily and cheap if he doesn't want the carb. He's out a few bucks and some time. That's most likely one of the OP issues. He can't get enough air through the carb without opening the blades so far it's off the idle circuit.

Or, I'm misunderstanding what he's saying. Which is possible. Any time you have to open the blades up to make them run that gets the blade past the transfer slot you need to drill the blades. Newer Holleys come with a built in adjustable bleed so you don't need that.

Between cars and two strokes I've been trying to get guys to shut the throttle to make them idle. Funny thing is, all the 2T heroes and gurus used to say you can't make them idle and be fast. Then came the "modern" 4T and those pigs have to idle. So yes, any IC engine should idle. On its idle circuit.
Understand he's saying he has not paid for the carburetor and if he just takes it back he doesn't have to use it...
 
Buying parts for it and drilling holes in it something he's committed to this questionable carburetor. He has one that works fine. you can just add $100 to what he was going to spend on this one and probably could buy a brand new one...
 
Heck, For $100 get used carb with a decent calibration baseline. With a limited $$ and time budget, this is the way to go.
That or tune and modify the '600' Carterbrock for better top end in the 1/4 mile.
 
Heck, For $100 get used carb with a decent calibration baseline. With a limited $$ and time budget, this is the way to go.
That or tune and modify the '600' Carterbrock for better top end in the 1/4 mile.
Or like I do just run two of them!:thumbsup:
 
Thanks for the advice guys. I was trying to get the timing at different rpms last night and my timing light started acting stupid. I have a Mac tools digital dial back to 0 timing light. I set rpm at 2500 rpm and 33 advanced as I did before. I went to bump the throttle to 3000 and the timing light was instantly set on 45. I did not move it. I relived the mark back up and it said 50. I brought it back to idle and had 33 at idle. Mind you I am not hitting the adjust button on the timing light. I will grab my old rotary dial and recheck.
As far as the carburetor, I have the secondaries acting as an air bleed which is what drilling holes in the primaries would do and I am able to completely close the primaries which in my mind should allow the mixture screws to work. They do not have any effect. I need to make sure the mixture ports are completely clear. Maybe try another metering block off of another carb I have laying around? I will post what I find. I am back at work now though so it will be late tonight
 
I was told a dial back timing light on an MSD equipped car won't read properly. I have a timing tape, so, I just use the standard type of light.
Maybe try reducing the secondary some, while opening the primaries. possibly having the primaries too far closed is affecting the transfer slots.
I also have carbs that I could never get to run right. I just bought a Quick Fuel carb, and moved on.
 
I was told a dial back timing light on an MSD equipped car won't read properly. I have a timing tape, so, I just use the standard type of light.
Maybe try reducing the secondary some, while opening the primaries. possibly having the primaries too far closed is affecting the transfer slots.
I also have carbs that I could never get to run right. I just bought a Quick Fuel carb, and moved on.
I had heard that about using a dial back on MSD. I don’t have an MSD on this car so I should be ok.
 
Thanks for the advice guys. I was trying to get the timing at different rpms last night and my timing light started acting stupid. I have a Mac tools digital dial back to 0 timing light. I set rpm at 2500 rpm and 33 advanced as I did before. I went to bump the throttle to 3000 and the timing light was instantly set on 45. I did not move it. I relived the mark back up and it said 50. I brought it back to idle and had 33 at idle. Mind you I am not hitting the adjust button on the timing light. I will grab my old rotary dial and recheck.
As far as the carburetor, I have the secondaries acting as an air bleed which is what drilling holes in the primaries would do and I am able to completely close the primaries which in my mind should allow the mixture screws to work. They do not have any effect. I need to make sure the mixture ports are completely clear. Maybe try another metering block off of another carb I have laying around? I will post what I find. I am back at work now though so it will be late tonight


The engine idles off the secondary side as well. Jacking the secondaries open is just as bad as jacking the primaries open. Like I said, you may need holes as big as .187 in each primary butterfly. They are cheap. Buy two new ones and drill them. If you still don't like the carb, put the original ones back in.

If you are jacking the secondaries open to close the primaries you just robbed Peter to pay Paul.

Edit: don't swap metering blocks from different carbs. The emulsion can be different, and all that affects air bleed calibration and other stuff.
 
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