thomas short
Member
What Edelbrock carbs can be used in place of dual Carter's on a stock 409 manifold. Also what happens with the idle mixture screws on front carb. Do the carbs need rejetting to work?
Edelbrock dual carbs on 409 manifold
- Thread starter thomas short
- Start date
Those carbs are at the recommended range of Eldebrock sizing. Assuming they were purchased as a dual four barrel set up and the stock jetting and rods are in the carbs probably air adjustment is all that is needed. I recommend throughly reading the manual that comes with those carbs as it is a wealth of information I wish we had many years ago. The air adjustment process is throughly explained so no need to go through it on here. Since you are much closer to optimum cubic inches and hopefully cam specs I think you are ready to go. I had to go to minus 2 steps tune to get my 348 correct but yours is a different circumstance. Also don't forget the timing adjustments as that is one item that really got mine "correct"
Robert
PS just looked at your photo. if you can borrow a manometer check those air elements Fine for 348's but "maybe" not for big brother 409's.
Original AFBs are superior carbs to the Edelbrock. Most Edelbrocks work really well but sometimes they have problems (internal casting flaws I think but have never cut one open to see) and if you get one with those problems you cannot make it work no matter what you do to it. If it were me I would put the 3720/3721 327 carbs on that intake.
Factory calibration for the 409 was .1015 primary jets, .0635 secondary jets, and .0635x.069 metering rods. Don't worry about the .0005 if you put .101x.063 jets and .061x.069 to .064x.070 or so metering rods in, you should be OK. You can find out what is presently in the carbs you plan to use with pin gauges and a dial micrometer. If you need more jets or rods Edelbrock jets and rods work fine in an old AFB. Once you get the set installed you can get dead nuts on the calibration with an air/fuel mixture measuring device and data logger but the above should work forever for a street car.
Adjust the idle mixture screws by turning them all the way in and then backing all four out 1 3/4 turns initially. Then fine tune to get maximum vacuum at idle after you get the setup on the engine. Go round and round watching the vacuum gauge and turn each screw in until the engine starts to stumble and then back it out 1/2 turn, then go to the next screw, etc., etc. Two or three circuits of this should do it.
The secondary air valve in the secondary (front) carburetor should have at least 1/2 ounce lighter weights than that valve in the primary carb. You can accomplish this by drilling holes in the weights on the valve that goes in the front carb. If you don't do this when you floor it the engine may kind of pause before the secondary carb opens all the way. Not bog, just kind of pause at a power level somewhat between the rear carb all the way open and then both all the way open. If this is just a street car don't worry about this weight thing. Original 409 secondary valves have a half moon shaped reduced area machined out of both of their weights.
I mainly do Pontiac 421 Super Duty dual quad setups for people but have done some 409 sets and have restored/rebuilt hundreds of AFBs.
Factory calibration for the 409 was .1015 primary jets, .0635 secondary jets, and .0635x.069 metering rods. Don't worry about the .0005 if you put .101x.063 jets and .061x.069 to .064x.070 or so metering rods in, you should be OK. You can find out what is presently in the carbs you plan to use with pin gauges and a dial micrometer. If you need more jets or rods Edelbrock jets and rods work fine in an old AFB. Once you get the set installed you can get dead nuts on the calibration with an air/fuel mixture measuring device and data logger but the above should work forever for a street car.
Adjust the idle mixture screws by turning them all the way in and then backing all four out 1 3/4 turns initially. Then fine tune to get maximum vacuum at idle after you get the setup on the engine. Go round and round watching the vacuum gauge and turn each screw in until the engine starts to stumble and then back it out 1/2 turn, then go to the next screw, etc., etc. Two or three circuits of this should do it.
The secondary air valve in the secondary (front) carburetor should have at least 1/2 ounce lighter weights than that valve in the primary carb. You can accomplish this by drilling holes in the weights on the valve that goes in the front carb. If you don't do this when you floor it the engine may kind of pause before the secondary carb opens all the way. Not bog, just kind of pause at a power level somewhat between the rear carb all the way open and then both all the way open. If this is just a street car don't worry about this weight thing. Original 409 secondary valves have a half moon shaped reduced area machined out of both of their weights.
I mainly do Pontiac 421 Super Duty dual quad setups for people but have done some 409 sets and have restored/rebuilt hundreds of AFBs.