Edelbrock Carb Question - Chevelle Tech
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post #1 of 9 (permalink) Old May 19th, 17, 5:24 PM Thread Starter
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Randy
 
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Edelbrock Carb Question

I friend of mine decided to switch the original Quadrajet off the 70 Chevelle he bought new in 1970 with an Edelbrock carb. The carb was new but someone removed both idle mixture screws. Can anyone give me an idea what the initial starting point is as far as how many turns out on these screws. I've worked with a lot of carbs but never one of these. Thanks for any help.
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post #2 of 9 (permalink) Old May 20th, 17, 5:30 AM
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Geoff
 
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Re: Edelbrock Carb Question

Better to start rich than lean, so that the engine keeps running long enough to adjust the idle mixture. Start with 2.5 turns from seated.
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post #3 of 9 (permalink) Old May 20th, 17, 11:14 AM
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gary
 
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Re: Edelbrock Carb Question

Mine are 1 turn +- after warm as said above^^.
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post #4 of 9 (permalink) Old May 20th, 17, 5:00 PM
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Re: Edelbrock Carb Question

put the Q-jet back on. The Eddie carb is not a step forward from a Q. At all.
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post #5 of 9 (permalink) Old May 21st, 17, 12:36 AM Thread Starter
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Re: Edelbrock Carb Question

Quote:
Originally Posted by Tom Mobley View Post
put the Q-jet back on. The Eddie carb is not a step forward from a Q. At all.
That's exactly what I told him to do. It worked perfectly for 47 years so why change it. Its a 300HP 350 with a 4 speed and it runs out great with the Quadrajet. The guy who sold him the Edelbrock said to start at 6 turns out which I knew was wrong.
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post #6 of 9 (permalink) Old May 21st, 17, 3:59 AM
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Re: Edelbrock Carb Question

1-1-1/2 turns same as any carburetor I would put the Q-jet back on as well but if he really wants to run the eddy then to each their own.

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post #7 of 9 (permalink) Old May 22nd, 17, 4:57 AM
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Re: Edelbrock Carb Question

Not all carbs are 1-1 1/2 turns out. Holleys were often 1/2-1 turn out. TQs are often 2.5 turns out. Depends on the discharge hole size, taper on the screws & thread pitch. TQs use a very fine thread & shallow taper on the screw.
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post #8 of 9 (permalink) Old May 22nd, 17, 7:51 AM Thread Starter
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Re: Edelbrock Carb Question

Thanks for the help. I know the Quadrajet that is on the car now is at 3 turns out and it runs fine. I'm still trying to talk him out of the swap. I told him it has worked just fine for the last 47 years so why change it.
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post #9 of 9 (permalink) Old May 23rd, 17, 7:25 AM
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Re: Edelbrock Carb Question

Sometimes we need to swap parts out in search for more power or possibly better drivability.

I have 3 special carbs I usually try on everything they are sooo close to each other that it is hard to tell you swapped carbs at all .
A Qjet , a 750 double pumper and a 750 AFB all have been tweaked and the holley tweaked the most with porting, epoxy and thinned throttle shafts.
All are within 1/2 MPG of each other.. the most difference between them was 10HP.

The holley was 10HP better on a performer RPM intake and the Q jet was 10 HP better than the Holley on a ported Iron Q jet intake.
On one intake one carb would be slightly richer.. then swap to a different intake and it flip floped the rich carb was now the lean one.

By just a little bit , 3/4 of a point. Average was within 3HP .

The 10HP difference was at the very top of the RPM range. Peak HP.

It does not hurt to try different things. Just keep the old stuff.
Right now I am playing with tuning my 385 and swapping between a 750 AFB 9000 series and 750 Edelbrock performer.
Both run completely different.
Still working the jetting.springs and secondary air valve over.
Fun to play sometimes.
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