Author Topic: Is my carb too big for my 383?  (Read 22538 times)

Offline Bluemonster71RT

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Is my carb too big for my 383?
« on: June 19, 2015 - 10:29:12 PM »
Though I cannot drive my car yet to know for sure (lack of wheels and tires) I have a feeling that my Edlebrock 750 is or may be to much for the engine.
Long story starts now:
 Back before the "restoration" started and the carb that came on the car when my dad bought it new off the lot was a Holley 750(so he claims) and ever since I can remember, the car ran too rich. Over the years a few of his trusted mechanics tried to tune it "right" but my dad always said "it still doesnt run the way it used to". Which was my clue to figure that at some point in time he had the carb replaced. Though he swears that a Holley came on it new. I don't doubt that but I don't think it was a 750 double pumper. Anyway one day I said "F" this thing and bought a Holley street avenger 670. The car finally came alive. What a difference it was to drive the car. It was 1000% better.
 SO flash forward to where the engine was being rebuilt and I was discussing the 670 and the guy said that it would now be too small. So I sold it and stole the edelbrock 750 from the wifes car. Now as I fired it up for the first time, it seems that it is too rich and even the air idle screws don't do to much. Today after running for about 10min I shut it down and a few min later I needed to restart it and it wouldn't until I held the pedal to the floor.
HERE'S THE MEAT Is it still possible that with the much larger cam, 12:1 pistons and 88cc Edelbrock heads, a 750 still be too much? I guess the assumption was that those items would want a larger carb.
Any way to know for sure prior to road testing it? It will be some time before I can get some wheels.     
1971 Challenger RT 383 4spd




Offline Chryco Psycho

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Re: Is my carb too big for my 383?
« Reply #1 on: June 19, 2015 - 10:44:19 PM »
Mopar put a TQ 800 cfm on 340s , a 750 on a 383 is fine

Challenger - You`ll wish You Hadn`t

Offline Bluemonster71RT

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Re: Is my carb too big for my 383?
« Reply #2 on: June 19, 2015 - 10:55:20 PM »
One would think. I just can't seem to lean out the idle. Hell I cant even stall it with the a/f adjustments and I just set/made sure the floats were good. Edelbrock says that can happen with a big cam though. :dunno:
Maybe smaller rods? Or reserve all things till I can actually drive it?
1971 Challenger RT 383 4spd

Offline aris_unlimited

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Re: Is my carb too big for my 383?
« Reply #3 on: June 20, 2015 - 09:34:18 AM »
I've heard that edelbrocks can be difficult to tune. I have never had to do it myself, so take that how you will. On the other hand I have heard pretty good things about street demon carbs. Course you could just slap an efi system on there and theoretically solve all your problems.
Cuda is gone :(

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Offline HP_Cuda

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Re: Is my carb too big for my 383?
« Reply #4 on: June 20, 2015 - 12:05:02 PM »

First you need to find out what jets you are running. Because if someone fooled with the carb before you then you'd have this problem.

Take the 750 off and do a tear down, it's better to know then to keep guessing at a problem.

750 should not be a problem for a 383.
1970 Cuda Clone 440 4 speed - sublime green
1970 Cuda 383 4 speed - yellow - SOLD

Offline Bluemonster71RT

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Re: Is my carb too big for my 383?
« Reply #5 on: June 20, 2015 - 12:08:55 PM »
First you need to find out what jets you are running. Because if someone fooled with the carb before you then you'd have this problem.

Take the 750 off and do a tear down, it's better to know then to keep guessing at a problem.

750 should not be a problem for a 383.
I did that before I put it on the car, bought the complete rebuild kit for it. It was all back to out of the box spec when I fired the engine.
1971 Challenger RT 383 4spd

Offline HP_Cuda

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Re: Is my carb too big for my 383?
« Reply #6 on: June 20, 2015 - 12:10:52 PM »

Wow, then are the floats set correctly?

Does the car idle with this carb and if it does what kind of vacuum are you getting?
1970 Cuda Clone 440 4 speed - sublime green
1970 Cuda 383 4 speed - yellow - SOLD

Offline polarbear123

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Re: Is my carb too big for my 383?
« Reply #7 on: June 20, 2015 - 01:12:33 PM »
Take out the 2 rods on top of carb. One on each side and step them down one size.

Offline 734406pk

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Re: Is my carb too big for my 383?
« Reply #8 on: June 20, 2015 - 09:11:34 PM »
Your metering rod springs may be to strong for this engine with the lower idle vacuum. If the metering rods aren't seated, you won't be able to adjust the carb with the mixture screws. You might want to get a Holley carb for this engine so you can tune it correctly.
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Offline Chryco Psycho

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Re: Is my carb too big for my 383?
« Reply #9 on: June 20, 2015 - 09:44:29 PM »
Your metering rod springs may be to strong for this engine with the lower idle vacuum. If the metering rods aren't seated, you won't be able to adjust the carb with the mixture screws. You might want to get a Holley carb for this engine so you can tune it correctly.
Exactly
 the springs could be too strong , if you remove the covers while idling the rods should be down if not you need lighter springs

Challenger - You`ll wish You Hadn`t

Offline Bluemonster71RT

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Re: Is my carb too big for my 383?
« Reply #10 on: June 21, 2015 - 08:52:25 AM »
Alright, thanks friends!  I will locate my vacuum gauge and find out whats doing and also check out the rods/springs.
1971 Challenger RT 383 4spd

Offline djw383

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Re: Is my carb too big for my 383?
« Reply #11 on: June 21, 2015 - 09:07:55 AM »
I have a Holley 750 DP with mechanical secondaries on my much milder 383 than yours and it works well. When it was on the dyno it made more power with the 750 than the 850....


Offline Bluemonster71RT

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Re: Is my carb too big for my 383?
« Reply #12 on: July 17, 2015 - 09:01:25 PM »
Still waiting on being able to test everything. I'm in the middle of an oil pump swap. I'll post info as soon as I can run it again without losing oil.
1971 Challenger RT 383 4spd

Offline Racer57

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Re: Is my carb too big for my 383?
« Reply #13 on: July 17, 2015 - 10:28:30 PM »
Mopar put a TQ 800 cfm on 340s , a 750 on a 383 is fine

True, but are/were they measured the same way as modern carbs are with the same efficiency  ? Did a 750 flow the exact same air/fuel as a 750 does now ?

Offline Strawdawg

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Re: Is my carb too big for my 383?
« Reply #14 on: July 17, 2015 - 11:27:33 PM »
Measurement for four barrel carbs were established somewhere in the '50's at 1.5 inches mercury of wet flow.  It has remained the same altho I remember some company started ratings their units by measuring dry flow which gave them about 8% more....

The thermoquad was rated by the same standard as today's carbs.

The larger the carb, the more tuning that may be involved.