How much carb is too much carb

[RemCharger]

Testing the theory

 

[lewtot184]

View attachment 1616891
Testing the theory

I know a guy who's raced two of those old small afb's on a tunnel ram for years.

 

[RemCharger]

I know a guy who's raced two of those old small afb's on a tunnel ram for years.

Sounds like some sort of "induction claimer class".

 

[lewtot184]

Sounds like some sort of "induction claimer class".

I think just an old afb die hard. Anyhow it worked good for him so what can say.

 

[RemCharger]

I think just an old afb die hard. Anyhow it worked good for him so what can say.

I actually kept 2 for that reason, but as the years roll on I'll just use them on some stock turds. 1 big carb is enough for me

 

[lewtot184]

I actually kept 2 for that reason, but as the years roll on I'll just use them on some stock turds. 1 big carb is enough for me

I like a bunch on top,....lol!

 

[Orig69]

Hello all. So like the title says, how much carb is too much carb? It got me wondering if i have too big of a carb or i got something else going on.

I have a 69 sport satellite wagon. I pulled a 383/727 out of a 68 fury. It has a freshened upper end, but stock bottom end. I have an edlebrock torker intake and a rebuilt holley 4 barrel, single pumper carb. (3310-3 series, electric choke, vacuum secondary). I have gone through and verified that the points are set correctly (gapped and cleaned) and that the timing is set to 10 degrees (as per factory, for now). I have 12-13 inches of vacuum, i have size 74 jets in the carb with a 6.5 power valve, dont recall the squirters size, but i think they are a 38? I am running right close to 13.7 /13.9 air fuel ratio (as with a AF meter on the tail pipes, a little rich i know). I am at 6450ft of elevation (Rocky Mountains).

I know that mopars love a bit more advancement in the distributor, but i am still getting popping and back firing through the carb (probably ruined that power valve by now) but i have little to no throttle response at low speeds and then it occasionally stalls out. I cant even power brake the car without it stalling.

Which made me think that maybe, the carb is too much. If I remember, the 383s came with a 600 or 650 from the factory, at least for the ones who didnt have a 2 barrel.

Id love some input. Thanks.

View attachment 1615519

It looks like your engine does not have a PCV valve. That would make it run richer than normal, and a few other things.

 

[Viewsonic]

Wow! this thread got more attention than i would have expected. Sorry for the late reply everyone, ive been rather busy dealing with work and life.
anyways i will do what i can to reply to everyone, because i did leave out some more information and i will get to it.

That is a really low idle vacuum reading. A stock cam should be producing well over 18" of vacuum.
The beauty of vacuum secondary carburetors is that they are on demand devices....they only give what the engine needs.
The 1980-89 318 4 barrels in Police cars were ThermoQuads and when Carter closed their doors, the GM Quadrajet was used. These are 800 cfm carburetors but the vacuum secondaries allowed them to operate just fine and pass strict emission testing.

ideally the vacuum would be 18", however, depending on cam and elevation, that plays a large factor in it. the best ive been able to achieve is about 12.5-13".

I have a 750 cfm holley on
a 366. Burns rubber for
half a block. 4200 ft
elevation. Your 74 jets seem
rather large, as I'm running
66's. The rule of thumb is to
drop 2 jet sizes per 2000 ft
of elevation from sea level
on sea level set set up
Holleys. Accelerator pump
cams also come into play
as your carb will need a
steeper delivery ramp. I use
a orange pump cam
mounted on hole position 1.
These are just rule of thumb
ballpark, but hopefully gets
you to narrowing down the
problems.

and i had a feeling that the jets were too large as well. i have a gentleman helping me and this car is going to be a cruiser, maybe get on it here or there, but he was going for max horsepower and max power. which is nice, but thats not what i wanted to achieve. my plan for the car is to drive and cruise around. one thing i know is that this motor is older, and its been around the block a time or two, and the compression and cylinder leakage test numbers are where i want them to be. so i wasnt worried there. but yes, i agree that i need to step down the jets and put a different cam gear on it. that will hopefully be this weekend.

Almost sounds like a micky mouse valve job where they sank the valves and did not equalize the stem heights, so the valves do not close properly causing poor performance if it has a stock cam and lifters. Maybe do a compression test.

the head was freshened up, meaning that it was pulled off, cleaned, valves removed, carbon cleaned off, checked for out of round and then reintalled with new seals. the guides were not terrible, not perfect either but still within spec. when i did a compression check the first time, it was all over the board. once we cleaned and freshened the heads, the compression was way more stable (both warm, cold, dry and wet) and the cylinder leakage dropped to a reasonable amount across the board. not rebuilt heads, but cleaned up and reused. the lifters and cam were also inspected at that the same time and wasnt any apparent issues that had to be addressed right away.

I would say you have a tuning issue rather an over-carb situation.
Having really started learning the tuning side of carburetors in the last year or so, I'm appreciating how small differences can have a huge impact e.g added headers and car wouldn't run properly without backfiring. Upped the primary jets 2 sizes and it was fixed.
Now I'm playing around with an Edelbrock AVS2 650. Runs like a scalded cat on full throttle but is weak when loafing around and has a bog I'm struggling to get rid of. It's all in the tuning, and I'm no expert.
Watch some YouTube videos or better yet find an old school tuner to help. Get a vacuum gauge if you haven't got one and start playing around. Make the changes one at a time and write down what you are doing
I'm sort of enjoying the tuning process but even the weather has an impact so it's not easy.

I understand that, ive been watching a lot of vidoes. still trying to learn how to dial in carbs too. im more efficient with EFI (generation i grew up in) and just trying to get it figured out. i will dial back the jets and do a cam gear change and see how that helps. still a little worried about the backfiring and why its doing it. i ordered an AFR gauge to help better fine tune the mixture, because i dont want to run rich and wash out cylinders and have high carbon build up.

Get your timing dialed in (initial, advance rate, and total) before you even start messing with the carb. I would bet you need more initial.

this is what i was working on, i was verifying at my timing was on the dot, points cleaned and gap'd correctly and that was all in order. i set it to factory 8-10 degrees and will advance from there. just takes a little time

You likely need at least 16 degrees initial timing.
I usually run a lower vacuum power valve at these high altitudes.
Make sure fuel pressure and float level are correct.

Now, the real stuff. Pull carb and check how much of the transition slot is exposed.
It's not unusual to have to drill the throttle plates to maintain idle while reducing the amount of exposed transition slot exposure.
Higher altitudes actually makes the idle circuit run leaner. Less air pressure in the carb bowl.
Usually have to increase the idle restriction size in the metering block, likely to at least 0.032"

and thats what ive been reading, that the mopars love 12-15 degrees. i will try jumping it up to at least 13-14 just to help. what power valve are you running? i was told to take my vacuum and cut it in half for the power valve. that puts it at a 7.0 or 6.5. i rebuilt the carb and i redid every little part in it. i will double check the transition slot. i will also check into the idle restriction size. thanks for the input.

Your carb isn’t too big. Maybe a vacuum leak? Does the idle go pull-up & down? I suggest you put that carburetor back stock and adjust/modify from there as needed & I agree you need to advance your timing

no vacuum leak, does not pull up or down. i will be adjusting the timing as needed as well.

Ir could be a cam timing problem.

ive adjusted everything back to stock and will be adjusting as needed.

I agree. Retarded cam timing or ignition timing. After getting the carb mix screws set correct and i like to do it with a vac gauge. Turn them out 1/8 turn each til you get max vacuum in drive. I would start with the mix screws at 1.5 turns out. Make sure the pumps are set to immediately squirt as soon as you open the blades. After setting carb correctly, you still have same problem, look at the ignition timing and then the cam timing. I am assuming there are no vacuum leaks.

i will be doing that this weekend with any luck.

Honestly

GET RID OF THAT INTAKE MANIFOLD for your application

A nice dual plane will change everything in regards to LOW THROTTLE RESPONSE

Then we can start talking carburetors

height wise, its about 2" taller than the stock intake/carb with a spacer. however, i should still have some response.

My guess is your problem is a little more than tuning adjustments.

I think we have way to little info to even start.

Did the motor run fine before you're "freshened upper end"?
What is the history of the motor before the freshened-up?
What was freshened and how?
What is new, used, or rebuilt?
What is the history of the carb?
What is your idle rpm when you get 12" of vacuum?
How does it idle when you are in gear?
How does the exhaust smell at an idle - does it burn your eyes?
When you cruise at say 40 mph, how does it run, what happens when you give it some throttle at that speed?
Is there anything it seem do do okay?

Your problem could be:
Something not right in the carb
Crossed or bad spark plug wire(s)
intake to head leak
carb to intake leak,
other vacuum leak

If the motor ran fine before - focus on the things you touched or did.

1. no the motor ran like crap. i was having excessive cylinder leakage and a blown headgasket on passenger bank.
2. the motor was pulled from a 68 fury that had sat for a while. i did my due diligence of oiling the cylinders before moving the pistons up or down.
3. i mentioned this above.
4. all used, rebuilt carb but done meticulously with every little bit cleaned and every gasket/seal replaced
5. carb was pulled from a running engine and sat for years.
6. idle is around 650/700, in gear around 800ish
7. not running super rich, but should be around 14-ish. i ordered an AFR to determine that.
8. while cruising, if i punch it theres not much, but higher rpms it starts to pick up.
9. it hasnt overheated yet lol

i am setting everything back to factory setting and going from there

69 Sport Satellite Wagon

Boat of a car

"but i have little to no throttle response at low speeds and then it occasionally stalls out. I cant even power brake the car without it stalling."

6450 Elevation

Probably high gears



Single Plane Intake Manifold

i understand that its a heavy car and the motor, at best was 335 crank horsepower. i understand that i wont be spinning the tires and lifting the front end, but i should be able to get up to speed without holding up the rest of the town or stalling out.

 

[Viewsonic]

First, I'd recommend a different dual-plane intake, that manifold does not belong on your stock application. Second, the Holley 3310 is a great carb, a very versatile piece we'd install on many various engines, it's fine if the systems working as designed.

the gentleman i purchased this intake from ran it on his 383 in his roadrunner and he ran it for years trouble free. couldnt tell you if it was stock or not, but i figured for 50 bucks and no problems with it, seemed like a good gamble. and the carb is the carb i chose because of how versatile it is.

You might want to verify TDC mark on the dampner. If it's slipped you'll never get the ignition curve correct. 383's aren't very good at producing torque. The intake manifold makes that problem worse.

ive verified timing to the T. while doing so, verified distributor and made sure points were propperly gapped and set.

Another thought is altitude. If your over 5000ft above sea level a re calibration will be needed. 74 jets should be too fat.

As far as vacuum goes high elevations will noticeably reduce vacuum. I live at around 700ft and the best vacuum I can get at idle with a stock cam, intake/carb, with a good clean burn is 16". If by chance the short block has lower compression pistons (2bbl or worse) along with a single plane intake, and low oxygen percentage, and poor timing curve power will be in the toilet.

that is what i am feeling, i will be tuning it back down and trying again

Probably too rich. Find out what the factory jetting was on the 3310 and go down at least 6 sizes for your altitude. Advance the timing until it's hard to crank then back off a little.
Probably not the best intake manifold for a heavy car either. Perfomer or a stock one would make it more responsive.

i will be doing that

Wont idle and pops thru carb is a lean indication. Vac leak or poor fuel transition first to check. Make sure timing is correct before you do anything.

no vacuum leaks and timing is set now. i verified that recently.

I have a 69 383 with a TM6 and a double pumper flowed to 930, it runs 12.50s.
Guess I'm the wrong guy to ask about carb size lol.
But seriously, the 3310 is the best carb for that application. Congratulations on not running an edelbrock power choker

ive dealt with several edelbrocks and i dont really like them. some people stand behind them, but the onces ive dealt with have been a bigger pain than what i like. but im also somewhat new to carbs and tuning them.

It looks like your engine does not have a PCV valve. That would make it run richer than normal, and a few other things.

no pcv valve, but i do have a breather on the passenger side. if i could find the parts to install a breather on my driver side i would, however i cannot find the mickey thompson valve cover baffles for it. i havent resorted to making one quite yet, but i think thats what im going to have to do.




thanks everyone for the replies, i am hoping to do some more tuning this weekend and see how it goes. i have to go get gas and i pray that it makes it to the gas station and back. i run 91 octane, ethanol free, but im getting low. i will try to stay in touch with the thread.

 

[6PKRTSE]

I have never had any issues with using what some would say to big of a carb on any of my street cars.
-I have Eddy 1407 (750) on my New Yorker.
-I have a 850 double pumper on a +.030 383 on my Roached Runner.
-I have a +.030 440 with sixpack (1350 cfm) on my Charger.
-I have two 1050 Dominators on my 528 Hemi on my Challenger.

 

[Orig69]

no pcv valve, but i do have a breather on the passenger side. if i could find the parts to install a breather on my driver side i would, however i cannot find the mickey thompson valve cover baffles for it. i havent resorted to making one quite yet, but i think thats what im going to have to do.

A PCV valve will make the engine run so much better. This is what the PCV valve looks like.

 

[Don Frelier]

. while cruising, if i punch it theres not much, but higher rpms it starts to pick up.

This is a classic indication of retarded cam timing.
Not to be confused with ignition timing.

 

[WileERobby]

the gentleman i purchased this intake from ran it on his 383 in his roadrunner and he ran it for years trouble free. couldnt tell you if it was stock or not, but i figured for 50 bucks and no problems with it, seemed like a good gamble. and the carb is the carb i chose because of how versatile it is.

So, your want to put a smaller carb on a single-plane intake manifold, that's on a stock engine in a heavy station wagon, merely because the manifold worked ok on someone else's lighter car, which you have no idea what mods were done on that engine, and it was only 50 bucks. Ok.

 

[451Mopar]

The altitude kills vacuum readings, the reading is actually pressure differential. I don't think I have seen 15+ inches of vacuum on any of my older V-8 engines at 6,000 ft altitude.
Connecting the vacuum advance to full manifold vacuum should help idle / low speed compared to the ported vacuum carb connection. Again, the ported vacuum signal is dependent on throttle opening. There are ways to adjust total vacuum advance and the canisters spring pressure as how it reacts to vacuum, sort of like recurving the mechanical advance.

Tuning carb and ignition takes time and more parts / tools than you might expect.
With affordable EFI, and the junk gasoline sold today, I have been converting over to EFI on my cars. If just starting with EFI, there is a steep learning curve.

 

[AR67GTX]

It all depends on the engine. Remember a 302 Z28 came with a 780/800 Holley. And as Kern Dog mentioned, vacuum secondaries will only provide the air flow the engine can demand.

 

[Moparfever65]

Vacuum reading's too low. I'm going with vacuum leak.

 

[BrettL]

69 Sport Satellite Wagon

Boat of a car

"but i have little to no throttle response at low speeds and then it occasionally stalls out. I cant even power brake the car without it stalling."

6450 Elevation

Probably high gears



Single Plane Intake Manifold

So this might sound crazy but I used a vacuum gauge to set my initial timing at the max amount of vacuum and it’s worked great for me. As far as the torker intake goes I ran the torker II for over 30 yrs and had lots of similar problems with a 750 double pumper. Just recently switch to the performer RPM and an AVS 800 and it’s brought new life to my Ride tons of low end torque. I’m pretty sure the specs on that torker are in the higher rpm range. Just my 2 cents.

 

[Orig69]

no pcv valve, but i do have a breather on the passenger side. if i could find the parts to install a breather on my driver side i would, however i cannot find the mickey thompson valve cover baffles for it. i havent resorted to making one quite yet, but i think thats what im going to have to do.

You should check the valley pan for damage with all that backfiring and popping going on.

You can install the original valve covers if you have them.

 

[Viewsonic]

A PCV valve will make the engine run so much better. This is what the PCV valve looks like.

View attachment 1619144

I will check into this. i know pcvs help, i just have a basic straight through breather on mine, i wasnt wanting to blow out gaskets and seals. ideally id like to install a second one on the driver side, but the valve covers didnt come with that and id have to special make some splash covers for it.

This is a classic indication of retarded cam timing.
Not to be confused with ignition timing.

I was worried that maybe my cam might a bit wore or the timing chain is wore out. i should have checked it, before installing the motor, but i didnt. guess i have something to do this weekend.

So, your want to put a smaller carb on a single-plane intake manifold, that's on a stock engine in a heavy station wagon, merely because the manifold worked ok on someone else's lighter car, which you have no idea

and thats what i thought too. maybe too much carb for the car. i will double check the specs of the intake, and maybe look at another intake, but for the moment i was hoping to make this one work. kind of ballin on a budget right now.

what mods were done on that engine, and it was only 50 bucks. Ok.

the only "mods" is being cleaned up, new gaskets, the intake and valve covers. it is stock, other than the heads being removed, cleaned up, new seals and gaskets. its stock with unknown mileage. the intake was only 50 bucks, the gentleman had pulled his motor and put something else in and was selling off his extra parts.

The altitude kills vacuum readings, the reading is actually pressure differential. I don't think I have seen 15+ inches of vacuum on any of my older V-8 engines at 6,000 ft altitude.
Connecting the vacuum advance to full manifold vacuum should help idle / low speed compared to the ported vacuum carb connection. Again, the ported vacuum signal is dependent on throttle opening. There are ways to adjust total vacuum advance and the canisters spring pressure as how it reacts to vacuum, sort of like recurving the mechanical advance.

Tuning carb and ignition takes time and more parts / tools than you might expect.
With affordable EFI, and the junk gasoline sold today, I have been converting over to EFI on my cars. If just starting with EFI, there is a steep learning curve.

i rarely see that much vacuum on olders cars as well, all the ones ive dealt with havent been much more than 15. i know rings and cams make the world of difference and when im pullling 12-13 inches, i figured i was doing decent for an older motor with unknown mileage. if i was pulling 7-8 inches, then i would worry. I thought the vacuum advance had to be connected to manifold as well and not the carb, but a friend suggested otherwise. i was going to make this change. and yeah, after looking at what all ive dumped into this, i feel like i should have gone efi, but im here and might as well do what i can to make it work. im much better tuning efi than carbs (just the generation that ive grown up in) but i also wanna learn how to tune carbs. i have several holley kits for tuning (squirters, cams gears, jets, trick kit) and i understand none of that means diddly squat when you dont know how to tune it, but its a start.

It all depends on the engine. Remember a 302 Z28 came with a 780/800 Holley. And as Kern Dog mentioned, vacuum secondaries will only provide the air flow the engine can demand.

i was not aware of that that they came with such a large carb. but yes, a good sealing engine does make a world of difference.

Vacuum reading's too low. I'm going with vacuum leak.

no vacuum leaks, just an older engine at higher altitude. this has been mentioned above.

So this might sound crazy but I used a vacuum gauge to set my initial timing at the max amount of vacuum and it’s worked great for me. As far as the torker intake goes I ran the torker II for over 30 yrs and had lots of similar problems with a 750 double pumper. Just recently switch to the performer RPM and an AVS 800 and it’s brought new life to my Ride tons of low end torque. I’m pretty sure the specs on that torker are in the higher rpm range. Just my 2 cents.

yeah, i will check into this. id honestly be happy if i could just take off without having to feather it and not take forever to move. i know the car is heavy, and that plays a lot into it. i will check into a different manifold but for now would like to try to make this work.

You should check the valley pan for damage with all that backfiring and popping going on.

You can install the original valve covers if you have them.

i will check out the top end this weekend when i go to double check the timing chain. and the valve covers are good, i had one that was leaking but i put on some cork/rubber gaskets and they stopped leaking. so one issue down.

i appreciate everyones reply. i am still tinkering with it. i havent worked on it as much as ive liked, and its hard finding time with 4 kids and a demanding job. but i have taken everyones advice and opinion and put it on the list. ive reversed some of the work that has been done (larger jets, smaller squirter, different power valve) and gone back to "factory". ive reset the timing and hopefully nothing else is wrong, but i will checking into all of that here real soon.

i will post again when i get there. thanks.

 

[WileERobby]

No, you missed my point. It's not the "size" of the carb.