Carb Questions..HELP!

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CUDACOX

CUDACOX

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O.K. I need some help. I have a 750 Edlebrock carb on my mild 340. 40 over cast crank and pistons,10to1 compression, 491 lift cam,decent ported heads,202 stainless valves,gasket matched LD340 intake,Stock 68-70 Manifolds, Stock 2" exhaust,3:55 posi. My question is for all you guy's/gals way smarter than me!! ... Would a 650 or? carb work better for my application? I have a little stumble from a dead stop when punching it and even from dead stop easing the pedal..I have heard several stories of over sizing carbs etc.. Has anybody here tried different carbs/sizes? and what do you think works best? I'm very greatfull for any comments/help. Thanks in advance!
 
I could be very wrong, but I am pretty sure you could use a 750 Holley for your 340. I'm sure those with more facts will chime in.
 
650CFM may or may not work better for your combo, but I think the stumble has more to do with set-up or adjustments than the size of the carb. Is it a Brand New carb? If not is the accelerator pump working correctly? Too much or too little shot & it will stumble. Also you need to have clean circuits in the carb. Also make sure everything is right with the ignition system. Timing set correct? Cap, rotor, coil & wires all in good condition?
 
Lonewolf3165 said:
650CFM may or may not work better for your combo, but I think the stumble has more to do with set-up or adjustments than the size of the carb. Is it a Brand New carb? If not is the accelerator pump working correctly? Too much or too little shot & it will stumble. Also you need to have clean circuits in the carb. Also make sure everything is right with the ignition system. Timing set correct? Cap, rotor, coil & wires all in good condition?
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Carb is not new but everything else is.It just doesn't seem to have the punch out of the whole.
 
That carb should work for your build. As LW said accelerator pump, dirt etc. Jetting maybe. I never cared for the Eddy carbs I did use one at one point on an old chebby truck I had and it seemed to do OK.

As far as your over carbing question, it would probably do OK with a 650cfm. I just did a quick calculation here http://www.carburetion.com/calc.asp and a 340 revved to 7000 with a mild build came up with 654 CFM.
 
are you running a stock converter if you are I would say its a good possibility .
 
Have you tried moving the accelerator pump linkage up or down a hole in the actuator arm?
 
I ran that carb on a simpler set up all new good stuff but it to was not what I was hoping for strong mid and upper but not all that out of the hole long story short I have been running thermoquads ever since
 
Sounds like accelerator pump issues you dont have too much carb work on the one you have its probably something real simple.
 
You need likely to remove the top of the carb to get to the accel discharge squirter's and change them out to a larger size - or jst drill them with wire drills, say .030 and if its .030 right now, make them .034

I had to do that to my 500 cfm carb - but I run dual 500 carbs

Those types of boosters work better with 600 and 500 crm carbs. Why dual carbs were the thing till Holley 750 - 950's came along in the late 1960's

Edelbrock doesn't care, people want 750 "Carters" they can buy 750's but the smaller carbs work better but choke the engine down....why dual 500's were the thing.

Too bad Edelbrock no longer sells a dual quad intake for the SBM
 
Sounds like it's running lean. Moving the accelerator pump linkage to the hole closest to the pivot point will give the most pump shot. That may help if it isn't already set up there but it may still be lean in the jetting. It's super easy to jet the primary's up by changing the metering rods so if you don't have a tuning kit you may want to buy one. Download the tuning guide from eddy's website and it'll show you which rods to use to richen it up. As for the sizing, IMO a 650 will give you better driveability and quite possibility better take off but loose a little up top (like 4500 and up). Probably no more than 10 hp diff. though and it may not even be that much with that extremely restrictive 2" exhaust your running.

BTW: What's the duration of the cam at .050" ?
 
750 Holley Vac Sec. New out of box, no adjustments, other than idle (yes, I had to save up $300 for it but with a new motor that took me more than a year to build, and the money for the parts, I wasn't taking chances). I have a set up real close to yours-340 std bore ,10.5 to1, steel crank, 2.02 ported 589 heads, MP 484 hyd cam, points ign.,headers, 2.5" exhaust, hi vol oil pump, deep pan, MP rockers, moly push-rods, 1/2" oil crossover in lifter valley, and an old Holley strip dominator, 2200 MP Stall, 4.10 Gears. SS springs. No hesitation at all in any throttle position. With old, dry tires, when I floor the gas, It jumps right up to 7500 RPM and trys to rip the front tires right off the ground, with minimum rear tire spin. They are 60 series. This combo is in a 66 B Body (all steel)....:burnout:
 
I run a 750 DP on my 340 Craig with no issues. My wifes uncle who set mine up lives in Arthur and id really good with carbs if you want his name.
 
Which Edelbrock 750? There are two Performer (AFB) type carbs - One is a lean replacement for the GM/Ford big block carbureted egnines and will be perpetually lean because even the air bleeds are leaner. The other is the universal performance 750. The cheap 750s are almost always the 1411 which is the lean one can comes with electric choke. The performance one is the 1407 which is only available new with the manual choke, but the electric can be added for extra cash.
Now - all that being said - with the 3.55s, manifolds, and 2" exh the 650 would probably be more responsive with a decent cam and ported heads.
 
moper said:
Which Edelbrock 750? There are two Performer (AFB) type carbs - One is a lean replacement for the GM/Ford big block carbureted egnines and will be perpetually lean because even the air bleeds are leaner. The other is the universal performance 750. The cheap 750s are almost always the 1411 which is the lean one can comes with electric choke. The performance one is the 1407 which is only available new with the manual choke, but the electric can be added for extra cash.
Now - all that being said - with the 3.55s, manifolds, and 2" exh the 650 would probably be more responsive with a decent cam and ported heads.
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You are correct,mine is the 1411. Just debating on if I should spend the money on a new better carb or play with what I have.Anymore help?/ I'm greatfull for all comments so far!!
 
I went from the Thermoquad with a 72 spreadbore stock manifold to this http://www.summitracing.com/parts/SUM-M08600VS/?rtype=10 with a Weiand aluminum intake and I am quite happy with it so far. It was inexpensive and the throttle response is very crisp.

I only have a 318 with a similar lift cam, headers and 2 1/2 inch exhaust. The difference is very noticeable though. You might want to step up to a 650, this carb is a 600cfm.
 
750 Eldys are know to cause problems, you can tune it but it will take trial and error.
I have about the same motor with a little more compression and lift in the cam, the cam grinder recommend a 700 holley DP.
 
Hi Craig. I don't have personal experience with the Eddy carbs, although they probably react to tuning similar to the Carter's they copy. I don't doubt that the model you have has a very lean idle/main circuit as "moper" spoke about. Seems to be alot of complaints about that perticular carb. I believe it can be richened up enough and made more drivable thru some trial and error tuning with jets, rods and step up springs. Pretty sure that would cure your problem but could make it less crisp in the throttle response area? With the cost of carbs these days it's probably worth some experimentation. I know you've tried to keep a stock looking theme with the car, which is beautiful:D, so if you decide to go to a replacement i think the Thunder series 650 AVS would probably be your best choice. I am a fan of Holley's and if you went that route, the 670 Avenger would be my choice. It would require a throttle adapter, dualfeed fuel line and monkeying with the hard line. I vote to tune 1st, Thunder carb 2nd, and Holley conversion 3rd.

A few links to see what i was talking about............
http://www.summitracing.com/parts/EDL-1806/
http://www.summitracing.com/parts/HLY-0-80670/
http://www.summitracing.com/parts/HLY-20-7/
 
Hi Craig,

I'm running a 650 Eddy on my 340. Off line throttle response is great (instant wheel spin) even with the old Torker intake...Though it feels like it could use more carb when pulling at top end. That said, like the other's indicated, I would think that 750 of yours would run real nice with a bit of a tune. Disclaimer: My experience level with tuning carbs is basically to bolt em on, get it to idle nice and drive...:dontknow: . I'm sure you'll get her sorted out.

Pat
 
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