no low end?

[2000.malibu.ls]

Well it's not necessarily too much carb, it sounds like your secondaries are slow to open, which means it could be a tune problem.

Does this happen: when in first gear, you smash the pedal to the floor and it lags then starts to pick up slowly?

yes? tuning problem?

First tune the carb so it's idling nicely, has the ideal idle mixture (which you can test with a vacuum gauge, google for more info), and set your floats at the optimum level if needed.

Make sure you have a good vacuum connected to your secondaries, and it sounds like you need to tune the secondaries to open sooner. This you have to tune by driving and testing (it’s recommended to test in high gear), because they are supposed to only open under a load when you mash the pedal to the floor. Vacuum secondaries open at different rates with different diaphragm springs inside. Lighter springs = open sooner, stiffer springs = open later. What you’re lookin for is a spring that makes your secondaries open a tad late after you step on it and ease into the extra power. You shouldn’t feel a jump with vacuum sec. Google around to find some instructions or kits with different sized springs. It wouldn’t hurt to call edelbrock and get their advice also.

There are also tricks you can do to find out if your secondaries are opening, google and see if you can find some

It also sounds like your power valve could be opening too late. You’ll need a vacuum gauge to test this and buy the correct valve.

Here’s a test you can try to make sure your power valve is working – turn the idle mixture screws in all the way at idle and if it sputters and dies then the power valve is working.

I agree 750 cfm is kinda big, but it can fit just about any engine if tuned properly. You might also look into jet sizing. But you don’t need a new carb, just spend some time and work tuning, go check out a book on tuning carbs at the library.

its a brand new carb though? nothing should be worn? so just try tuning and move from there?

 

[SScamino]

"Well it's not necessarily too much carb"

"I agree 750 cfm is kinda big"

LOL, what? Your right though, tuning would help it, but I would personally never go 750 unless it makes 450 horse, or its a sbc 400. It's not nessarily your intake but because Im not sure of that what intake do you have? single plane or dual plane? With a single plane again you gain high end, and lose bottom end. Remember if you do switch carbs you'll notice that bottom end will make the car snappy when hitting the gas because of low end power, but high end will be less, you really wouldnt need 750 cfm until like 6000 rpm, so a 600 or 650 would be fine. In my 400 hp 355 I have and eddy 600

 

[custom442]

"Well it's not necessarily too much carb"

"I agree 750 cfm is kinda big"

LOL, what? Your right though, tuning would help it, but I would personally never go 750 unless it makes 450 horse, or its a sbc 400. It's not nessarily your intake but because Im not sure of that what intake do you have? single plane or dual plane? With a single plane again you gain high end, and lose bottom end. Remember if you do switch carbs you'll notice that bottom end will make the car snappy when hitting the gas because of low end power, but high end will be less, you really wouldnt need 750 cfm until like 6000 rpm, so a 600 or 650 would be fine. In my 400 hp 355 I have and eddy 600

sorry man, 750 is a little big but perfectly fine if tuned correctly. People do 750's on 305/307 engines...

 

[custom442]

its a brand new carb though? nothing should be worn? so just try tuning and move from there?

Yes, tune it like you would for a tune up, get everything idling nicely then try to test for the correct power valve and change out diaphragm springs. This shouldn't be too expensive at all. I'll bet edelbrock can even send you a book or pamphlet on how to tune your carb. & if it's new then you haven't burned your power valve out 😀 (unless something went terribly wrong)

Out of the box your 750 will run a little sluggish, but that's not saying it can't perform as good or better than anything else out there. I mean this isn't a high dollar drag car, so as long as it's close....

 

[SScamino]

True, but thats way too much carb for that engine, I think the calculations come out that all a 305 needs is a 550cfm, If horsepower is the name of the game go for the 750, it will make more power with the 750, the 600/650 will have a good balance of horsepower and torque.

 

[custom442]

Well, working with what he has, it'd cost much less to tune and buy a few pieces than to ship it back and go through the warranty hassle etc. and then buy a smaller carb. It's not like he's gaining any real gas mileage or gaining/losing any real useable hp. The reason people say you need a certain cfm carb is for better throttle response, as malibu ls is finding. But it's not saying it can't be made to have better throttle response.

I really don't think it's too much carb, I mean the online calculators might say that but in reality.... I have a 770 cfm holley on my 383 and it's perfect

 

[2000.malibu.ls]

Im gunna try and tune, I dont have the money to spend on carb parts, Its not like Im drag racing it yet, and Im going to be building a b/a motor after I finish the car, because sadly, the motor Im working with seems to be quite shot as far as the cylendars and heads.

 

[custom442]

Im gunna try and tune, I dont have the money to spend on carb parts, Its not like Im drag racing it yet, and Im going to be building a b/a motor after I finish the car, because sadly, the motor Im working with seems to be quite shot as far as the cylendars and heads.

what's the part number on your edelbrock?

I asked because you might have an easier time than I did with the holley, just looked and saw many new edelbrocks have an adjustable vacuum secondary (AVS) screw... so no need for the old style spring change

 

[jrm81bu]

And they don't have power valves. 😀

 

[custom442]

And they don't have power valves. 😀

my holley is showing, I need to cover it up 😳