Okay here is the deal,

I am running a 302 (bored .30 over) with an edelbrock 600 carb. I was told that this is too much carb for the engine and that is why I am burning gas like a big block. Is there anyway I can fine tune this carb or does ebay get my money for the 500 carb. I am also blowing about 8-9 psi into it when idling and that is way to much fuel (edelbrock's website information). So the ? is do I turn down the psi and see where that gets me or both - change out the carb and turn down the psi......HELP!!!!!!!!!!!!!!!

 

Yes, a 450-500 cfm carb would have been better for the 302 than the 600 but I doubt if the venturi size is the main problem with it "burning gas like a big block". I'm a cheapskate so if it were mine and the carburetor is new I'd just keep it for now with the idea of replacing it with a smaller carburetor at a later date. You can get a lot better gas mileage by keeping your foot out of the throttle than anything else. If the carb has manual secondaries you could disconnect the linkage so they don't open and that might help some. I used to do that years ago with Quadrajets. What ratio rear end gear are you running?

 

The 500 cfm carb is probably a better fit to your 302. I run the 600 cfm (#1406) on my 351C and it seems just right. But before you spend $250 or so to replace the one you have, try buying an Edelbrock Carburator Calibration Kit (p/n 1487) for about $40. It gives you a selection of needles, seats and springs so you can dial that carb in. I solved my Edelbrock carb problems with it and am very satisfied. You may not need to deal with the fuel pressure at all, after you swap to leaner needles.

The Edlebrock recommendation on psi has to do with the float's ability to shut off the fuel. Too high a pressure would overcome the float seat and spring. I'd guess that unless the carb is leaking fuel at the bowl, the float is shutting off the fuel pressure. However, you can install a fuel block to regulate pressure or swap to a different pump. I run a Carter electric pump that puts out 7 psi with no pressure problems.

BTW, if you are getting 10-14 mpg, that's about as good as it will get, depending on gearing and tire size. I run 26" tall tires, 3.50 rear and get 10-11 mpg on the freeway. Others here run taller rear gears, overdrive trannies and/or taller tires to get into the 20's.

 

Are you sure on that tire diameter, Randy? That's pretty small. My calcs say you are turning almost 3200 RPM at 70, is that what you see?

Highway mileage on a proper non-OD setup should be closer to 14-15 for a 302, IMO. 20's are pretty darn rare even with OD, usually the smaller engines and cruising at 55 not 70. We're pushing bricks thru the air!

 

Ross -

Yeah, I run P295/50R15 rear tires (26" tall). And I run about 3200 at 70. Wish I had an AOD! When I ran a 3.0 rear end, it was about 2700 at 70, but it didn't have that jump off the line. Give a little, get a little.

 

i am running 295/50R15 with a 9" rearend ratio of 3.25 and an AOD from an 85 cougar...

 

How about some 285/45 20' GT II's, thats what I have on my 79 F-150XLT/86 302 roller block (slightly built) with a 9" rear and 325's...mild cam but nothing til about 30-35 and then she takes off to about 90, am going to change the rear end for a better off the line...

 

You can run a 600 on your 302. I;m running the 600 Edelbrock on my 289 and it runs sweet. I use to run the Holley Double pump 600 and even a 750 Holley on my 289 and they ran real good. Actually, the bigger carbs run harder than the lean ones. I would advise you to get a Edelbrock carb calibration kit like Randy mentioned. 8-9 lbs of fuel is way too much. I've seen guys running blowers that regulate the fuel pressure to 6-7 lbs max. You'll need to put a fuel regulator on it or get rid of the fuel pump. The stock pumps which I use put out about 3-4 lbs if your lucky and they deliver more than enough fuel even under full throttle conditions. Unless your running a supercharger or dual quads with a engine that really demands the fuel, you don't need the high volume fuel pumps in which case you wouldn't be worrying about gas mileage. They look nice, but they don't work well and are a waste of money on stock engines. As for gearing and tire sizes, I believe what these guys are talking about is the lower the gears, the worse your mileage is as a rule. I'm running 3.50's in my truck and my mileage actually improved around town switching from the 3.00's that were in it, but it really drinks it if I cruise over 55 on the highway. I'd keep the carb and dial it in.

 

i was running the original rear-end in my truck but the fuel consumption was even worse...so when i switched to the 9" with 3.25 gears....fuel wasn't going as fast but still she drinks a lot....i have to travel 12-15 miles a day to work; mostly on the highway so you can understand my pain when I fill up with $25 bucks and in about 3-4 days i have to fill up again....(S_U_C_K_S!!!!!!)...try not to hit the pedal as hard because she will spin the wheels at the light... :-)

 

55- Try advancing your timing. The more advanced, the better your mileage. I advanced my 66 Mustang timing, and the mileage is super now. Just a thought!

 

i barely have the truck running now...i turned it way down and the carb is set really low....so the only option is the carb kit and a fuel regulator....maybe that combo will knock out the excessive fuel consumption.....BTW what is the best gear ratio for highway cruising with a 302/AOD combo? i'm running 295/50R15 with a 9" rearend ratio of 3.25 and an AOD from an 85 cougar...with an edelbrock performer intake 4 barrel and 1406 (600) 4 barrel....

 

Considering your running an AOD transmission, I think your fine withe gears you have now. It sounds like most of your driving is highway. 3.25's are a nice gear for your combo. I definitely get a regulator or change out the fuel pump. Not sure what you mean by turned it way down? and set really low?

 

I had the carb setup really high idle and then tuned it that way also...about a couple of months ago...i realized the mistake when the truck was pulling way too much in drive....