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Discussion Starter · #1 ·
Hi all this is new to me .I have a 73 barracuda it is a 40 over 340.
750 edelbrock
Performer intake
X heads 3angle valve job
Harland Sharpe roller rockers
2.02/1.6 valves
Comp cams 249-20-670-4
280 h 474 lift 240 duration 287 ex duration
9.4:1 compression
Hooker headers
727 trans
1800- 2200 stall converter
3.91 gears
Mickey thompson 295/45/17s rear tires. My problem is lazy off the line & I'm wondering if I have the right cam & carb .the carb is a 750 edelbrock.
 

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Been on the Aftermarket Specialist side for a while but I haven't had anybody rave about an Edelbrock carb. They all say they're too difficult to dial in and are very sensitive to temp/humidity/altitude changes. Just my $.02....
 

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Discussion Starter · #4 ·
Thanks paullybob I was also told to try a 650 edelbrock.Talked to a few people that had better luck with smaller carbs.If it's only my carb that's causing me trouble that's not to bad🤔
 

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Too much carb, Comp Cams is great for GMs but not for Mopar (get a cam from Hughes Racing Engines), would rather have a 3000 stall converter and the 3.91 is a little steep for the street and this combo, I'd rather be at 3.55.
 

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Having owned a carburetor shop and also being a Holley warehouse, I was just going to say "overcarbureted" and the mechanical secondaries don't help. What kind of advance curve and static timing are you running? One piece I will throw out there, your centrifugal advance needs to not start below your idle rpm, meaning your neutral idle rpm, otherwise you will have all kinds of problems.
 
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Having owned a carburetor shop and also being a Holley warehouse, I was just going to say "overcarbureted" and the mechanical secondaries don't help. What kind of advance curve and static timing are you running? One piece I will throw out there, your centrifugal advance needs to not start below your idle rpm, meaning your neutral idle rpm, otherwise you will have all kinds of problems.
I agree...............over carburetion is the biggest problem a lot of guys do on their cars. We used to run all types of carb and manifold setups on the dyno. I ran one of Gliddens pro stock motors for his Plymouth Arrow back in 1978?. Came with twin 650's if I remember right. Ran like a dream off idle and at the top end. For fun we put a couple Dominators on it. Had the biggest stumble you ever saw at low speed but once it got going at the top end 8400 rpm to 10,000 rpm it smoothed right out. And really it didn't make much more power than the 650's because of the manifold/head combo on the engine.
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Distributor vacuum advance should be ported vacuum, not intake manifold vacuum.
You want a high distributor vacuum from off-idle on up. Manifold vacuum drops low as the throttle is opened.
Can you hear any ping or detonation on warm WOT, or is the exhaust too loud?
 
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Too much carb, Comp Cams is great for GMs but not for Mopar (get a cam from Hughes Racing Engines), would rather have a 3000 stall converter and the 3.91 is a little steep for the street and this combo, I'd rather be at 3.55.
I like your statement but was wondering if you could explain the diff between Comp cams and Hughes cam and why ones is better for Mopar?
 

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Hi all this is new to me .I have a 73 barracuda it is a 40 over 340.
750 edelbrock
Performer intake
X heads 3angle valve job
Harland Sharpe roller rockers
2.02/1.6 valves
Comp cams 249-20-670-4
280 h 474 lift 240 duration 287 ex duration
9.4:1 compression
Hooker headers
727 trans
1800- 2200 stall converter
3.91 gears
Mickey thompson 295/45/17s rear tires. My problem is lazy off the line & I'm wondering if I have the right cam & carb .the carb is a 750 edelbrock.
Welcome to Allpar... you have one of my favorite cars sure would be nice to see some pictures
 

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Just for the record, I had an "overcarbureted" 289 Cobra engine in my 1966 Shelby GT350. I had dual Holley 465 cfm 4 barrels on it using an actual Ford intake that was from the 1966 Trans-Am series Mustangs. It would use all 8 barrels as the secondaries were vacuum operated and synchronized with a hose connected between the diaphragm housings.
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Make sure your ignition timing is right and that the mechanical advance is working. All timing should be in by 3000 rpm. Most small blocks like around 32 to 34 degrees total timing. Make sure the accelerator pump is working properly. Edelbrock carbs you can adjust the pump duration by moving the rod into one of three holes on the accelerator pump rocker near the top of the carb. Also you might just need bigger squirters. The accelerator pump basically enriches the fuel mix until enough air velocity is going through the venturies so the fuel then transfers through them. "Big" carbs can be tuned pretty easy to work on small engines. All thermoquads where a minimum of 800 cfm and they put those on stock 340's. I've never ran anything smaller the a 750 on all the 340 and 360 engines I've had. The last 360 was a junkyard magnum engine with a small cam and headers with a 830 holley double pumper in a 1987 Plymouth gran fury and that car ran 13.9 and would smoke it rear tires on the street.
 

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Discussion Starter · #14 ·
Too much carb, Comp Cams is great for GMs but not for Mopar (get a cam from Hughes Racing Engines), would rather have a 3000 stall converter and the 3.91 is a little steep for the street and this combo, I'd rather be at 3.55.
Yes I was always wondering if that 750 was to big . With 391 gears & the rear tires I'm running it seems like 355s on the rpms & speedo.
 

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Discussion Starter · #15 ·
Just for the record, I had an "overcarbureted" 289 Cobra engine in my 1966 Shelby GT350. I had dual Holley 465 cfm 4 barrels on it using an actual Ford intake that was from the 1966 Trans-Am series Mustangs. It would use all 8 barrels as the secondaries were vacuum operated and synchronized with a hose connected between the diaphragm housings.
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Make sure your ignition timing is right and that the mechanical advance is working. All timing should be in by 3000 rpm. Most small blocks like around 32 to 34 degrees total timing. Make sure the accelerator pump is working properly. Edelbrock carbs you can adjust the pump duration by moving the rod into one of three holes on the accelerator pump rocker near the top of the carb. Also you might just need bigger squirters. The accelerator pump basically enriches the fuel mix until enough air velocity is going through the venturies so the fuel then transfers through them. "Big" carbs can be tuned pretty easy to work on small engines. All thermoquads where a minimum of 800 cfm and they put those on stock 340's. I've never ran anything smaller the a 750 on all the 340 and 360 engines I've had. The last 360 was a junkyard magnum engine with a small cam and headers with a 830 holley double pumper in a 1987 Plymouth gran fury and that car ran 13.9 and would smoke it rear tires on the street.
Now you are making go way back in the dusty files in my memory. I didn't do many small block Mopars, I do remember that the Chevy small block ran best with 38-42° total advance (not figuring vacuum), Ford small block 36-38° total. With an automatic, I would stick a heavy set of springs in for test purposes and find what I needed for idle rpm to be tolerable in gear then use that + maybe 200 rpm for my advance start. As for all in by 3000, maybe, depended on the engine and application. The advance on the Cobra 289 was 12° static, 20° degrees mechanical in at 3500rpm, then an additional 6° in by 5000 rpm. This was on an 11:1 compression ratio short stroke (2.87") engine.
 

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I like your statement but was wondering if you could explain the diff between Comp cams and Hughes cam and why ones is better for Mopar?
For Mopars Comp takes their Chevy grinds and put them on Mopar shafts. They just don't make good power in Mopars. My '73 Challenger with a built 360 had a Hughes HEH2328AL cam with, 223°/228° duration and .506/.539 lift @ 111°. It made great power, sounded great and made just enough vacuum for power brakes. Hughes specializes in Mopars.
 

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The Edelbrock has two adjustments for the carb. One is a two step needle (there are two of them) and the squirter itself. As noted there should be three holes on the accelerator pump to adjust that, possibly needing more fuel thus leaning out, or too rich and flooding until the rpm increases. The needles, being two step, there are two diameters for the jets they sit in. The larger top diameter is for cruising, the bottom is a smaller diameter for greater acceleration. There is a table for the two step needles (also called metering rods), to adjust for different conditions you can use to dial in the carb performance.
One thing that will really help, and given you sound pretty capable in the build, is to get an O2/fuel-air ratio meter to know for sure where the sweet spots are to get the correct fuel/air ratio without burning pistons or overfueling and wasting the rings.
As far as the carb being too big for the build, 340s like lots of air, and no matter what size CFM it is, the engine will only use what it can suck in. I know, this is a debate we can have forever but there will never be a definitive answer one way or the other.
 

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Discussion Starter · #19 ·
Make sure your ignition timing is right and that the mechanical advance is working. All timing should be in by 3000 rpm. Most small blocks like around 32 to 34 degrees total timing. Make sure the accelerator pump is working properly. Edelbrock carbs you can adjust the pump duration by moving the rod into one of three holes on the accelerator pump rocker near the top of the carb. Also you might just need bigger squirters. The accelerator pump basically enriches the fuel mix until enough air velocity is going through the venturies so the fuel then transfers through them. "Big" carbs can be tuned pretty easy to work on small engines. All thermoquads where a minimum of 800 cfm and they put those on stock 340's. I've never ran anything smaller the a 750 on all the 340 and 360 engines I've had. The last 360 was a junkyard magnum engine with a small cam and headers with a 830 holley double pumper in a 1987 Plymouth gran fury and that car ran 13.9 and would smoke it rear tires on the street.
Thank you very much snow on the ground now can't do to much now but always appreciated.
The Edelbrock has two adjustments for the carb. One is a two step needle (there are two of them) and the squirter itself. As noted there should be three holes on the accelerator pump to adjust that, possibly needing more fuel thus leaning out, or too rich and flooding until the rpm increases. The needles, being two step, there are two diameters for the jets they sit in. The larger top diameter is for cruising, the bottom is a smaller diameter for greater acceleration. There is a table for the two step needles (also called metering rods), to adjust for different conditions you can use to dial in the carb performance.
One thing that will really help, and given you sound pretty capable in the build, is to get an O2/fuel-air ratio meter to know for sure where the sweet spots are to get the correct fuel/air ratio without burning pistons or overfueling and wasting the rings.
As far as the carb being too big for the build, 340s like lots of air, and no matter what size CFM it is, the engine will only use what it can suck in. I know, this is a debate we can have forever but there will never be a definitive answer one way or the other.
Thank you very much greatly appreciated
 
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