850 Carter Thermoquad flooding at low rpm

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Check the temp of the fuel pump , intake and carb base with a laser thermometer after the car starts to stuble. I've had to make thicker insulating type fuel pump and carb gaskets for a few builds because of ethanol boiling off in the pump at around 173 degrees F.
My bet is Heat soak in the fuel system somewhere. Probably at the fuel pump itself heated by the header tube. It would explain why it quits stumbeling when you get going because it's cooling off via air flow.
Headerwrap around the tube or a heat shield around the pump.
I ended up finding this on mine by simply pouring room temp bottled water on my fuel pump when it was doing the same one day. Once I got it home and measured my fuel pump temp it was 240F even though the block and head were 180.
 
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What kind of insulator mounting gasket do you have?
 
Edelbrock 9265 Square-Bore Heat Insulator Gasket for the carb.
I made an insulator fuel pump gasket out of the same material cut out with a dremel tool and thinned out. But don't go too thick with the material for the fuel pump gasket or the pump shot will be weak.
 
They can be great...Or a PITA.. Mine have all been great cause I took the time to make them right.... Customers & friends? A PITA cause they don't want to spend the time or pay someone to spend the time....
 
Now you see what we've all been saying. When they're right, nothing really compares.
There's no other sound that compares thats for sure. Tuning isn't really as bad as let on either when the proper steps are followed. I've fought with edelbrocks a heck of alot more and never get it quite right.
 
There's no other sound that compares thats for sure. Tuning isn't really as bad as let on either when the proper steps are followed. I've fought with edelbrocks a heck of alot more and never get it quite right.
Yeah well, you have a lot of mechanical ability, too.
 
This, was a common issue back in the day.... Low vacuum doesn't keep the metering rods down, the plugs get loaded up & soon the engine barely runs... Run the engine a little higher RPMs & the vacuum signal improves pulling the metering rods down & the plugs recover...

Pull the aircleaner & with the engine idling watch the metering rod yoke, it should stay fully down, if it's bouncing either increase the vacuum signal or reduce the spring tension on the yoke...
Great information, Now I have some homework to do
 
Dartfreak75 I am trying to get in touch with you can you send me a pm,trid sending you one and it says your box is full
 
Dartfreak75 I am trying to get in touch with you can you send me a pm,trid sending you one and it says your box is full
Hey bud just saw this yea my inbox is full. My gold membership expired and now my inbox is like 1000% percent haha to much to delete. So I gotta deal with it until I renew my gold membership. What's up?
 
Ok I'm confused;
Why would you run that 296* cam at 1500rpm for so many hours?
What were you thinking?
You wanna bet your engine oil smells like gas?
-------------------------------------------------------
Here's what I would do;
A) at your cruise-rpm of 1500 rpm; check your ignition timing and your manifold vacuum, then, disconnect the Vacuum advance and see if it changes. If it does, make a note of the mechanical timing by itself.
Next;
B) Run the rpm up to 1500 rpm, then fix it there for the rest of this test.
Reinstall the vacuum advance, if the rpm goes up, slow it back to 1500. Then
advance the timing; and if the rpm goes up, slow it back to 1500.
Repeat until additional timing does not cause more rpm.
C) Read the timing.
Whatever you read for timing, that is what your engine wants, at this rpm, to put the pressure peak in the right spot. It could by 20/25 or as high as 45/50, IDK BBs at 1500.
and, read the manifold vacuum, at this setting, then, compare what you see, to what you had in A) above.
If you cannot supply your engine what it wants, or close to it, then don't cruise there.
Here's what you need to know;
Your engine has a point in it its power-cycle, in the which the pistons will be in the optimum position to transfer the energy of the expanding gasses to the crank. All your attempts at adjusting the timing, is only adjusting the beginning of the burn time to make the peak pressure occur at that optimum point, which is around, 25 to 28 degrees AFTER TDC Compression.
If the pressure comes too early, it may cause problems, as the rod hammers into the crank, before it's ready.
If the pressure comes too late, then optimum power cannot be achieved as the piston is already running away from the expanding gasses.

This is especially crucial while cruising at steady rpm. Too early or too late will cost you fuel economy; and the loss of manifold vacuum causes other problems.
In your case, with that big cam, the pistons are pushing just inducted A/F charge, back up into the intake plenum as they round the bottom of the stroke and the valves won't be close to closing until the piston is over 72* past BDC, on it's way back up on the compression stroke now! This is why your manifold vacuum is so low at idle.
This is further complicated by the cam having some 80* of overlap, during which time, the headers are desperately trying to pull AF charge straight across the pistons and out the pipes. The slower the rpm, the more successful they will be.

1500 rpm is a terrible rpm to cruise that combo at, only made worse by lack of Ignition advance, which doesn't help the low manifold vacuum.

>>Listen, I ran a 292/108 cam in my 367@ .538 lift with 1.6 arms. I ran it with an A833 and 3.55s, for 65mph = almost 2900. Not a bad combo. but I was no fan of that rpm, nor the terrible fuel-economy.
So I installed an A833 overdrive which dropped the Rs to 2000, and guess what, the thing burned even more gas. That led me to figuring out why, and that is how I got to the above.
So I pulled that way-too-big-cam outta there in favor of a 270/276/110 cam And right away I was in business, so much so that I bought/installed a GVod, and dropped the cruise-rpm to 75= 1850, and that combo made the most mpgs I ever measured (with my Barracuda). But I tuned it to put the pressure peak right where it needed to be, then kept it there until the gas tank ran dry.
 
I've trimmed the metering rod spring about an 1/8th of an inch. Worked on my 440 with the 284-484 cam.
 
Some do say that. I don't.

Ok I'm confused;
Why would you run that 296* cam at 1500rpm for so many hours?
What were you thinking?
You wanna bet your engine oil smells like gas?
-------------------------------------------------------
Here's what I would do;
A) at your cruise-rpm of 1500 rpm; check your ignition timing and your manifold vacuum, then, disconnect the Vacuum advance and see if it changes. If it does, make a note of the mechanical timing by itself.
Next;
B) Run the rpm up to 1500 rpm, then fix it there for the rest of this test.
Reinstall the vacuum advance, if the rpm goes up, slow it back to 1500. Then
advance the timing; and if the rpm goes up, slow it back to 1500.
Repeat until additional timing does not cause more rpm.
C) Read the timing.
Whatever you read for timing, that is what your engine wants, at this rpm, to put the pressure peak in the right spot. It could by 20/25 or as high as 45/50, IDK BBs at 1500.
and, read the manifold vacuum, at this setting, then, compare what you see, to what you had in A) above.
If you cannot supply your engine what it wants, or close to it, then don't cruise there.
Here's what you need to know;
Your engine has a point in it its power-cycle, in the which the pistons will be in the optimum position to transfer the energy of the expanding gasses to the crank. All your attempts at adjusting the timing, is only adjusting the beginning of the burn time to make the peak pressure occur at that optimum point, which is around, 25 to 28 degrees AFTER TDC Compression.
If the pressure comes too early, it may cause problems, as the rod hammers into the crank, before it's ready.
If the pressure comes too late, then optimum power cannot be achieved as the piston is already running away from the expanding gasses.

This is especially crucial while cruising at steady rpm. Too early or too late will cost you fuel economy; and the loss of manifold vacuum causes other problems.
In your case, with that big cam, the pistons are pushing just inducted A/F charge, back up into the intake plenum as they round the bottom of the stroke and the valves won't be close to closing until the piston is over 72* past BDC, on it's way back up on the compression stroke now! This is why your manifold vacuum is so low at idle.
This is further complicated by the cam having some 80* of overlap, during which time, the headers are desperately trying to pull AF charge straight across the pistons and out the pipes. The slower the rpm, the more successful they will be.

1500 rpm is a terrible rpm to cruise that combo at, only made worse by lack of Ignition advance, which doesn't help the low manifold vacuum.

>>Listen, I ran a 292/108 cam in my 367@ .538 lift with 1.6 arms. I ran it with an A833 and 3.55s, for 65mph = almost 2900. Not a bad combo. but I was no fan of that rpm, nor the terrible fuel-economy.
So I installed an A833 overdrive which dropped the Rs to 2000, and guess what, the thing burned even more gas. That led me to figuring out why, and that is how I got to the above.
So I pulled that way-too-big-cam outta there in favor of a 270/276/110 cam And right away I was in business, so much so that I bought/installed a GVod, and dropped the cruise-rpm to 75= 1850, and that combo made the most mpgs I ever measured (with my Barracuda). But I tuned it to put the pressure peak right where it needed to be, then kept it there until the gas tank ran dry.


If the tune up is correct it will run at 1500 rpm until the cows come home or it runs out of fuel. And why would the oil smell like fuel?


I didn’t read the rest but I doubt I’d agree with how to find the best timing.

Edit: I read that mess and if you are suggesting to set cruise timing with no load that’s CrAzY nucking futs.

If that’s not what you are saying I apologize. Write it more clearly and try again.
 
Ok I'm confused;
Why would you run that 296* cam at 1500rpm for so many hours?
What were you thinking?
You wanna bet your engine oil smells like gas?
-------------------------------------------------------
Here's what I would do;
A) at your cruise-rpm of 1500 rpm; check your ignition timing and your manifold vacuum, then, disconnect the Vacuum advance and see if it changes. If it does, make a note of the mechanical timing by itself.
Next;
B) Run the rpm up to 1500 rpm, then fix it there for the rest of this test.
Reinstall the vacuum advance, if the rpm goes up, slow it back to 1500. Then
advance the timing; and if the rpm goes up, slow it back to 1500.
Repeat until additional timing does not cause more rpm.
C) Read the timing.
Whatever you read for timing, that is what your engine wants, at this rpm, to put the pressure peak in the right spot. It could by 20/25 or as high as 45/50, IDK BBs at 1500.
and, read the manifold vacuum, at this setting, then, compare what you see, to what you had in A) above.
If you cannot supply your engine what it wants, or close to it, then don't cruise there.
Here's what you need to know;
Your engine has a point in it its power-cycle, in the which the pistons will be in the optimum position to transfer the energy of the expanding gasses to the crank. All your attempts at adjusting the timing, is only adjusting the beginning of the burn time to make the peak pressure occur at that optimum point, which is around, 25 to 28 degrees AFTER TDC Compression.
If the pressure comes too early, it may cause problems, as the rod hammers into the crank, before it's ready.
If the pressure comes too late, then optimum power cannot be achieved as the piston is already running away from the expanding gasses.

This is especially crucial while cruising at steady rpm. Too early or too late will cost you fuel economy; and the loss of manifold vacuum causes other problems.
In your case, with that big cam, the pistons are pushing just inducted A/F charge, back up into the intake plenum as they round the bottom of the stroke and the valves won't be close to closing until the piston is over 72* past BDC, on it's way back up on the compression stroke now! This is why your manifold vacuum is so low at idle.
This is further complicated by the cam having some 80* of overlap, during which time, the headers are desperately trying to pull AF charge straight across the pistons and out the pipes. The slower the rpm, the more successful they will be.

1500 rpm is a terrible rpm to cruise that combo at, only made worse by lack of Ignition advance, which doesn't help the low manifold vacuum.

>>Listen, I ran a 292/108 cam in my 367@ .538 lift with 1.6 arms. I ran it with an A833 and 3.55s, for 65mph = almost 2900. Not a bad combo. but I was no fan of that rpm, nor the terrible fuel-economy.
So I installed an A833 overdrive which dropped the Rs to 2000, and guess what, the thing burned even more gas. That led me to figuring out why, and that is how I got to the above.
So I pulled that way-too-big-cam outta there in favor of a 270/276/110 cam And right away I was in business, so much so that I bought/installed a GVod, and dropped the cruise-rpm to 75= 1850, and that combo made the most mpgs I ever measured (with my Barracuda). But I tuned it to put the pressure peak right where it needed to be, then kept it there until the gas tank ran dry.
Wow, that’s more than I read in highschool. Thanks for the enormous amount of information. Some I understand and some I don’t (but I got a guy who can put it in perspective) I was running 355’s at 2900 the same as you and went to 323’s. Having said that the car acted the same. Drive 1/2 hour at 2900 and at an intersection and it idled poorly (not as bad as las5 going off). I figured the starting point is clean the carb, setup the timing. I have a mechanic who specializes in performance engines going to check everything over. This info that you provided is very valuable And greatly appreciated. Thanks again Ron D
 
I am not a mechanic but mechanically minded and looking for an understanding and solution. The car (had it about a year) has a 440 with 460-500hp, Carter 850 carb, with a Mopar Purple cam 296/.557. Overview….. Car fires up and runs nice. I had always noticed after going for a drive it idles rough at stop signs, and couldn’t put my finger on it, but it came to a head yesterday on a long slow drive. I live in rural Nova Scotia Canada and took my wife for a nice long drive along the coast. I probably drove the coast line for 2 hours at 1500rpm 40-45mph. After the first hour I noticed the car getting rougher as we cruised ( the tack would pulse periodically). Temp is solid 180. At the end of the 2nd hour (about 90% of the cruise). I stopped at an intersection it started sputtering badly and it was all I could do to keep the car running. I pointed the car towards home (1+ hrs)….. yep, we are in **** the bed mode. the car kicked and sputtered for the first couple miles and as I picked up the pace it felt a bit better At 2200rpm (once I got it there). The last 1/2 of the drives the car started to feel better. When I got closure to home (and braver) I gave the car a couple of good pulls and every one was better that the one before and when I returned home the car was running normal. I suspect that the fuel supply is too heavy at lower rpm and flooding the car. Looking for thoughts and education. Thanks in advance RonD
If you suspect flooding there are only a couple reasons...
  1. Fuel pressure too high
  2. Float too high
  3. Needle not sealing correctly
  4. Internal carb issues
Dana mentioned fuel pressure. I scanned through the posts and didn't see where it was ever checked. CHECK YOUR FUEL PRESSURE!
T in a gauge and get a reading. I have experienced 7 and 10+ pounds of pressure that can cause your issues. Anything over 5# is to much. Holley's can stand a couple more pounds but can still be an issue. Check the pressure and then you can check that off the list of probable causes.
 
If the tune up is correct it will run at 1500 rpm until the cows come home or it runs out of fuel. And why would the oil smell like fuel?


I didn’t read the rest but I doubt I’d agree with how to find the best timing.

Edit: I read that mess and if you are suggesting to set cruise timing with no load that’s CrAzY nucking futs.

If that’s not what you are saying I apologize. Write it more clearly and try again.
Just a follow up to my carb issues. I took the Dart to a local engine building shop and the tech took an interest. The nuts and bolts (with my limited skills to explain). He worked on my distributor for over an hour to give the big cam more advance at lower rpm. He suspected the car had low vacuum pressure at idle with the big cam causing the issue, and not dirt in the carb. He set the valves and made minor adjustments to the carb but never took it apart. I had the car for a 2 hour ride (at low rpm 45mph). No fuel dumping, idled great and will rip the tires off on take off. Car never worked better. Thanks for your insight that the car should work all day if set up properly. Cheers Ron D
 
Just a follow up to my carb issues. I took the Dart to a local engine building shop and the tech took an interest. The nuts and bolts (with my limited skills to explain). He worked on my distributor for over an hour to give the big cam more advance at lower rpm. He suspected the car had low vacuum pressure at idle with the big cam causing the issue, and not dirt in the carb. He set the valves and made minor adjustments to the carb but never took it apart. I had the car for a 2 hour ride (at low rpm 45mph). No fuel dumping, idled great and will rip the tires off on take off. Car never worked better. Thanks for your insight that the car should work all day if set up properly. Cheers Ron D


SWEEEEEEEEEEEEET! I can’t tell you how many times I’ve seen carbs get blamed for running shitty when it’s in the timing curve.

Glad you sorted it out.
 
I run an 850 thermoquad as well. They run very well indeed! My set up is fairly warm. 292 mopar cam 3.91's out back.
 
I am not a mechanic but mechanically minded and looking for an understanding and solution. The car (had it about a year) has a 440 with 460-500hp, Carter 850 carb, with a Mopar Purple cam 296/.557. Overview….. Car fires up and runs nice. I had always noticed after going for a drive it idles rough at stop signs, and couldn’t put my finger on it, but it came to a head yesterday on a long slow drive. I live in rural Nova Scotia Canada and took my wife for a nice long drive along the coast. I probably drove the coast line for 2 hours at 1500rpm 40-45mph. After the first hour I noticed the car getting rougher as we cruised ( the tack would pulse periodically). Temp is solid 180. At the end of the 2nd hour (about 90% of the cruise). I stopped at an intersection it started sputtering badly and it was all I could do to keep the car running. I pointed the car towards home (1+ hrs)….. yep, we are in **** the bed mode. the car kicked and sputtered for the first couple miles and as I picked up the pace it felt a bit better At 2200rpm (once I got it there). The last 1/2 of the drives the car started to feel better. When I got closure to home (and braver) I gave the car a couple of good pulls and every one was better that the one before and when I returned home the car was running normal. I suspect that the fuel supply is too heavy at lower rpm and flooding the car. Looking for thoughts and education. Thanks in advance RonD
Update on the carb issues. The car is now running fantastic. I took to an engine builder at R&D Performance Nova Scotia. He reworked the distributor, replaced the vacuum advance. It appears the issue was not dirt in the carb, but very low vacuum pressure. Thanks for everyone who took the time to provide suggestions. They pulled me in the right direction. Ron D 71 Swinger (aka “The Gypsy Queen”)
 
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