hey guys i have a edelbrock 750 mech. secondarie carb on my car and i wunt to get a little bettter gas milage and i heard that having vacum secondaries help out. is this true?? also wut would be the ideal cfm carb to get for my engine combo??

 

my money is on the camshaft causing the low MPG.

 

"...i have a edelbrock 750 mech. secondarie carb on my car..."

No you don't.

At least, not in the sense the term is used with respect to Holley carbs. And, there isn't any reason a vacuum secondary Holley carb would get better gas mileage than a mechanical secondary Holley carb if tuned identically and if you keep your foot out of it.

The carb you have does indeed open the secondary throttle plates via a mechanical link. But, actual flow through the secondaries is controlled via a flapper that opens more as demand increases. So, it achieves the same goal as the Holley vacuum secondary carbs via that flapper.

In general, you don't have a combo that is oriented towards fuel economy. Changing the carb won't help all that much towards that goal.

 

Agreed. A well tuned mechanical secondary carb will achieve just as good a mileage as a vac sec coarb, if you keep your foot out of it.

Also agreed, Edlebrock carbs are all vacuum secondary in operation.

 

no your wrong, i have a 1407 witch is a 750cfm manual choke mechanical secodaire carb. ok well do u think if i put a 650 on ther it would help out at all? or do u think if it does we are talkin leik 2 mpg

 

The engine will need to make some vacuum before you'll see decent MPG. Fix that, then worry about the carb.

 

89 : .... Physics hasn't changed since the last time ya posted
on this. Don't expect much difference on mileage on your motor
by changing to a 650cfm carb with or without vacuum secondaries as compared to your 750.
Either way they both need fine tuning.

But the biggest factor is still your camshaft.

 

Might wanna try a carb better suited for your application 1406 600cfm. If edelbrock thought a 750 would work well on a SBC they wouldent hessitate to rewrtie thier litturature and get $40 more a carb, would they? Mechanical secondary carbs are not forgiving like vacuum secondary carbs and they do flow fuel through the secondaries at 1/2 throttle according to my A/F moniter. A vaccume secondary carb of larger CFM is more forgiving because if the signal isnt there it will not flow the max CFM reguardless of throttle opening. An edelbrock will get better fuel economy in city driving assuming its the proper size because of its metering system so will a qjet if the plugs arent leaking. Power is another issuem Holleys DO HAVE better throttle responce and have proven to have more power. What kinda driving do you do city or highway? Edlebrock better for city, Holley better for highway, niether good with lead foot.

Now that said I'm biting the bullet and am going to get an 625 AFB or a 600 Edelcrap come monday. All my driving is city and when I got the holley I was driving mostly HWY and the holley was better for HWY. I cant afford 12/13 MPG city anymore, there goes 20hp but the carb will pay fot its self in 3 months accoding to my past AFB experiance.