C3 - 1970 Rochester Carb question

[Jeremy D.]

I have a 1970 300/350 4 spd. coupe that has a Rochester 7040507 EV 2893 carb on it, which due to the stampings, if I'm reading it right, is a '73 service replacement (?) L-46 ECS carb. The car runs great, no probs there, but I was wondering if due to it being an ECS carb if ther is any reduction in performance over the correct plain ol' 7040203 DB carb. I GUESS that the carb size is the same....The rest of the car is stone stock, and runs great. Am I right in my date decoding, and since I'm just driving it and not showing it, is it worth it to get a non-ECS carb for it to get a little more snort? Also, ther are 2 screws on the front of this thing, which I would assume are mixture screws. Am I correct? I can't find any info on this carb at all, other than the Tech guide.

[Jim T.]

Re: C3 - 1970 Rochester Carb question

You can have a "little more snort" in my opinion with your 70 350/300 if you replace the carb with a Holley 6210 double pumper. Having a four speed with the double pumper you have complete control as to when you use the huge secondaries while the primaries are small like your current carb. I have used the Holley 6210's on my 68 327/350 4-speed and my 70 350/300 automatic since about 1973. Never regretted spending that $60.00 for new Holleys. The 6210 is a 650 and all you will need. A feature I like about having a Holley is being able to remove the air cleaner lid after my Corvettes have not been driven for awhile, using a big syringe and injecting fresh gas into the front fuel bowls. This replacement of evaporated fuel gives instant start up for my cars, no cranking of the starter to pump fuel to the carb. So easy to do. Start up is more like a modern day fuel injectted car. I even used my original dual snorkel air cleaner on my 70 with the Holley installation and my original open element air cleaner on the 68 with a little modification that can be changed back. To save your original fuel line, recommend replacing the steel line from the fuel pump to your current carb and make up a new steel one. This double pumper will be more active than your experience with your LT-1 cars, you control the action. I am not familar enough with the Demon carbs, nice looking carbs though.

[Clem Z.]

Re: C3 - 1970 Rochester Carb question

507 is a 1970 calif corvette carb and the only parts different are the throttle baseplate,float bowl and the air horn,no internal parts

[Jeremy D.]

Re: C3 - 1970 Rochester Carb question

Are the butterflies the same size, though? Is the float bowl the same capacity, or smaller? I'd like to stick with a Rochester as I don't want to change the manifold, retain my heat riser/choke, and adapters suck. The only things not original on my motor are the fuel pump and the carburetor, and I just picked up the correct pump. Also, am I right in my date deciphering? And am I right thinking the screws on the baseplate are mixture screws? This is the first car I've had with a Quadrajet, so I gotta go to school all over again!

[Patrick H.]

Re: C3 - 1970 Rochester Carb question

The differences between the two carbs are nominal; not enough for all the worry you're giving it. They are the same size, and if I took the numbers off one of each and let you inspect them it'd take you a while to figure them out.

Your date deciphering is correct.

Those are the IDLE mixture screws, correct.

Just spend the next 5 years looking for the correct number and dated carb, and drive it in the meantime. The car won't care about the numbers.

Patrick

[Jim T.]

Re: C3 - 1970 Rochester Carb question

Jeremy if the reference to changing the intake is for the Holley 6210 it is not required, I used the original intakes on my 68 and 70 and the chokes work with the original heat riser/choke and no adapters are required. The Holley 6210 is of the same spread bore design as the Quadrajet. It is a bolt on replacement.