I want to replace the AFB on my dead stock, except for carb and manifold, 300 cu. in. engine with a newer Edelbrock 600 cfm carb with electric choke. I have located a company that will change out the throttle plate shafts so I can retain the stock transmission linkage and kickdown. My question is, is the 600cfm too large for this engine, it's a lot less expensive than the 500cfm unit, but if it won't perform then I'll have to go with the smaller unit. Driveability and gas mileage are my main concerns. The AFB is just not working out to my satisfaction and I think it has something way wrong with it. It has been rebuilt twice and still is a gas pig and terrible idle quality. I know there are myriad other things that could be causing my problems and I've worked on everything, vaccum-timing-leaks-electrical-etc., now I want to see if a carb change will do anything. Thanks for your input.
I have the Edelbrock 500 on both of my cars and they seem fine. I've never tried the 600, so I can't make the comparison. The convert gets about 18mpg on the highway. I haven't calculated mpg on the other car yet. What company did you find to update the linkage?
My 300 has been running fine with a 600. If you have a 4-hole intake you may want to add a carb spacer to avoid interference with the throttle plates.
Edelbrock tends to tune the carbs a bit lean so it's usually a good idea to go up a size from what you would normally choose. If you're swapping out a 500 than a 600 would be an acceptible choice. The mileage may not be quite as good as the 500 though so that's something to keep in mind. I'd say go with whatever you feel is better on the budget and then you can always downsize the needles and stuff as needed if you want to lean it out even more.
All American Carburetors in Orange Park, FL will modify the Edelbrock so you can use the kick down and linkage. You must supply them with either an old AFB or two barrel so they can switch the control arm over to the Edelbrock. I got a quote from them for $50.00 back in October to do the change over. 904-214-6790 Thank you all for the info.
I used to run the big AFB from a nailhead on my Lesabre 300, and it certainly didn't go any slower. I don't think the gas mileage dropped off either.
Don't know if this is a concern of yours, it kind of sounds like, but the newer AFB's have the same sized neck as a quadrajet. In other words your stock aircleaner won't fit.
Very true. You have to run a new aircleaner. Or find or make an adapter. Also, the hole diameters for the secondaries in the manifold are too small- they are smaller than the venturis in the carb.... so as mentioned above, a spacer is necessary or else the butterflies on the secondaries will hit the manifold when they open. They do make a converter spacer (Summit has them) that reduces the larger square bores on the AFB to the old Rochester smaller square bores. Or you can enlarge the carb holes on the intake, as I did, and get better flow all around. I run an Edelbrock #1406 (600 cfm) on my 300 and it is perfect- a definite improvement, I think. Runs great right out of the box.
