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Old 08-07-2005, 02:22 PM   #1
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750 carb to big on a 302? carb guys please help!

Here is the engine i'm running....

Stock 302 bottom end with 160k miles, 9:1 compression, NEVER TOUCHED, just wire brushed clean the pistons, Anderson Ford Motorsports cam of unkown specs (has to be under .520 lift to clear the stock pistons), stock unported edelbrock performer aluminum heads 1.90/1.60 valves, 1.6 pedestal mount roller rockers, edelbrock victor jr intake (ported) and a speed demon 750cfm carb. for ignition i've got a MSD billet distributor, MSDdigital 6 box, and Jacobs ignition coil. Meizere electric water pump, electric fan, griffin radiator. Tranny is a stock T-5, pro 5.0 shifter, king cobra clutch, 3.73's out back. i've got a holley blue feeding into a 8an line from the pump to the regulator, then running 6an from the reg to the carb. BBK 1 5/8" long tube headers with a custom built 2.5" hpipe and flowmaster muffers, no tail pipes. that's basically the jist of it.

The carb and intake are overkill for the motor. They were what i had last year on my 347, but i'm thinking the carb for sure is overkill for this 302. Took it to thed dyno yesterday. With the carb still untouched from last year (being jetted for the 347) running 89octane gas and low timing, the car put down 331rwhp and 309torque. It seems like my accelerator pump is ****ed though ( i need a 50cc pump) b/c for the first couple seconds it spikes lean, and stumbles real bad on the dyno. Then it goes down but still lean to about 14:1. We didn't have any accelerator pumps on the dyno last night to swap it out with, so we ended up not really messing with any jets or anything and said F-it until we can get the accel pump figured out and come back later.

My main question is, do you think i can get this carb dialed in decently even with it being overkill? I've heard that a too big of carb will make you lean anyways, so if i'm jetting it up is it even going to help me? Or should i not even waste my time on this 750 and try to get like a 650? I was planning on swapping out the accelerator pump and going back tuesday to see if it smooths out at all. I might do it just b/c it's cheap and i'm curious, but i just wanted to get some other opinions on it. The engine definetly likes the RPMs. I made 3 runs, each time i revved it higher, and it made more RPM. on my 331 hp run, it was making peak HP and still climbing at like 6300rpm where i shut it off. I don't want to take it higher then that though b/c of the pedestal mount rocker arms ( i took it to 7k when i first had it done a week ago, and two of the rockers basically fell off, lol). let me know some of your opinions guys, i'm new to this carb stuff!
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Old 08-07-2005, 03:25 PM   #2
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i've got a 750 holley on my 308, not by choice though. a 750 speed demon seems like it would be worse.
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Old 08-07-2005, 03:54 PM   #3
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Yes, given time, some money and a O2 sensor I am sure that carb can be dialed in. THe down side, as has been mentioned if it is a BG carb, that flow rating is a wet flow rating, and unlike the stock holley rateing, your basically looking at about 820cfm or so in dry air flow rating.

It will be more difficult than many of the holley carb guys are thinking.

50cc accelerator pumps, I think not. 30's should be overkill. Remaping the accelerator pump cam will change how the shot comes on and how long it lasts. The BG carbs have the same pump shot cams as the holleys, but I don't know what the stock cams look like. Your going to have to jet up about 12% (of the actual jet surface area) So if you know the jet surface area, it'll be real easy to get jets.

So if you have a 67 jet in there, which is a .068" hole, 12% your going to add 3% at each jet, or go to a .070 hole, or a 69 jet should suffice. Pump shot is going to be a differnt story, the lower draw at the booster venturi will require an extended duration pump shot to crutch the carb till the booster picks up the pull.
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Old 08-07-2005, 04:04 PM   #4
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I talked to a few other guys today, one said the same thing. He said don't mess with the accelerator pump and he said i need bigger squirters. But overall i think this 750 is overkill, and i'm just going to slap on a 650 and try to go from there. I got a guy who is checking on a 650 holley with mechanical secondaries, no choked, and milled horn he has and i might try that out for the dyno this tuesday.
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Old 08-07-2005, 04:16 PM   #5
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Its not a bigger squirter, its a longer duration pump shot. You need to adjust the pump cam to make a longer squirt. GOing to a bigger squirter would result in a shorter pump shot, and probably just a wetted manifold surface as the excess fuel would just puddle.
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Old 08-08-2005, 05:41 AM   #6
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I had almost the same combo exept i was running a performer rpm and an E-cam. A 600 DP wouldnt rev above 4000rpm's ....upjet, down jet nothing but black smoke and stumbling. I put on a 750 DP and never looked back!! It was not as snappy as the 600, but it pulled good when the cam came on. I had alot of the same stumble off idle that you have but tore it apart before i got around to solving the stumble.

im currently putting that same combo back together exept im running a victor jr. we'll see how she goes.
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