holly carbs on a small block chevy

griffin #11

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i just changed out my old edelbrock carb for a bigger (650 i think) carb on my 350 small block. it has a mild cam intake exhaust and msd ignition. its in a '56 chevy apache and is street driven. what are some good tips on tuning these carbs...oh and its a double pumper carb.

thanks for the help.
 

partybarge_pilot

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Double pumper is going to be a little much on a mild 350. Run the mildest pump cams you can or your mileage will suck.
 

griffin #11

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ok well i was just experimenting. i had it laying around and jus wanted to c if it made any difference on performance. i know the edelbrock carb was a lil on the small side cuz the motor falls on its face when im at freeway speeds adn lay my foot into it. isnt that because its not getting enough fuel?
 

scottm

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What is the part number on the choke tower? It should be 4776-4781 (600 to 850 cfm). I would stay with a 600 or 650, though a 750 can be made to work too. If its dying out at freeway speed and under throttle, its not getting enough fuel, but thats likely due to a clogged filter or weak pump.
 

griffin #11

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yeah well i know its not the filter, im hoping its not the pump, ill check the part number tomorrow and give you that info...is ther any way to check exactly how big it is?
 

scottm

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The part number tells you how big it is.
 

partybarge_pilot

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i know the edelbrock carb was a lil on the small side cuz the motor falls on its face when im at freeway speeds adn lay my foot into it. isnt that because its not getting enough fuel?
Edelbrocks are set-up way lean out of the box. The need seroius re-jetting to work correctly.
 

griffin #11

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huh..ok now the small screws on the holley metering blocks are for idle mixture only right? wat other adjustments can i make without messing with the jets?
 

Sparky

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ok well i was just experimenting. i had it laying around and jus wanted to c if it made any difference on performance. i know the edelbrock carb was a lil on the small side cuz the motor falls on its face when im at freeway speeds adn lay my foot into it. isnt that because its not getting enough fuel?
Well, increasing the CFM of the carb is not the way to get more fuel. CFM only applies to the amount of air that it can flow. Unless you are spinning your engine up over 6500rpm, the Edelbrock will flow more than enough air. In fact, I personally prefer the Edelbrock/Carter style over the Holley (especially over the double pumper) because I think they have better street manners.

Go back to the Edelbrock and rejet. Get one of the Carter or Edelbrock tuning kits - it comes with jets, metering rods, and metering rod springs. There is also a good tuning manual that you can download from the Edelbrock website.
 

griffin #11

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well i only buzz it up to about 5-5500... thats still pretty high for the street. but i was just experimenting. im goanna drive it this weekend and tune it jus to c how it reacts to it.
 

Co-Dog

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Definitely a fuel issue with the edelbrock, main jet size and/or float level.

The double pumper will probably run great on the freeway, but that's about it. Without a lot of work, its gonna probably be tough to get it to run well in the low rpm range, especially when you punch it.
 

griffin #11

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yeah i put the edelbrock back on because ther were no vaccume hose to hook up the brakes and i had no time to go to the parts store and search for the right hose...im goanna stick with the edelbrock for now i jus need to get that thing dropping more gas... so can anyone help me with some tips for tuning these edelbrck carbs? ill also do some research on their site to do that..thanks again!
 

loufish

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so can anyone help me with some tips for tuning these edelbrck carbs? ill also do some research on their site to do that..thanks again!
First check your fuel pressure, then check flow...very easy to have a small crack in the vacum side of the fuel system sucking air and reducing pressure/flow...

I also agree that SB should be able to run just fine on the Carter 625...
 

griffin #11

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oh oh oh my bad i know wat ur saying ok i checked and the hose is in good condition..so thats not the problem
 

Co-Dog

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My Edelbrock experience is limited, but if you can tell me what type of carb it is, I can probably help you nail down the problem. There should be some numbers on there somewhere.
 
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