Paul_G
Well-Known Member
- Local time
- 7:07 PM
- Joined
- Dec 24, 2013
- Messages
- 2,156
- Reaction score
- 3,565
- Location
- Surprise, Arizona
The car is a 73 Charger with a 68 383 and 4speed manual, 323 geared sure grip. Basic street engine with a crane hyd flat tappet cam, 222°/234° @ 0.050", 114° lsa, 0.467"/0.494" lift. Stock 73 spread bore intake with adapter running a Proform 750 mech sec carb. Iron heads with long tube headers into short pipes with mufflers and turn downs.
The carb tune - It was rich all over, idling at 12.5 AFR, cruise at 13AFR, WOT at 11 AFR. First thing is to turn the carb upside down and square up the Transition slot opening as seen from the bottom below the throttle plate, do the primary and secondary. Then I jetted down from the stock 74P/80S jets to 72P/76S. Upsized the squirters from stock 31/31 to 37F/35R, switched the stock pink accel pump cam for a green pump cam. Upsizing the squirters and using a longer duration pump cam eliminated the off idle hesitation it was having.
Now the fun part, tuning the carb - The engine idled too low at 600 RPM with the transition slots squared up, and smoothest at very rich 12.5 AFR. I opened the secondary side throttle blades slightly to get the idle to come up. Secondary mixture screws were out less than 1/4 turn, poor control of the AFR on the secondary side. I put .017" wires in the secondary side Idle Feed Restrictions. That gave me some control over the idle mixture screws on the secondary side, out 3/4 turn now. Opened the primary side throttle blades about 1/4 turn of the idle speed screw. Idling now at 13.5 AFR about 800RPM. Cruise at low speed in the 16AFR range, light acceleration in the 13.5AFR range, WOT in the low 12 AFR range.
The distributer tune- Vacuum advance disco and plugged. When I started, the base timing was at 10° BTDC, mechanical advance at 35° all in by 1500, just Awful. Removed distributor and took out the mechanical advance plate. Welded up the outer ends of the slots about an 1/8". Ground smooth and cleaned. Put a slightly stiffer spring on the "light spring" weight. Adjusted the slot opening by grinding out some of the weld until I achieved about 24° base and 34° total. All in now about 2500 RPM. With vacuum advance reconnected full advance is now at 40° total at cruise.
It runs awesome! Very lean at cruise in the 15 to sometimes high 16 AFR range, should be easy on gas for a big block. Richens up nicely in the 13 AFR range for light acceleration, and safely rich in the low 12 AFR range to **** and get full throttle.
The carb tune - It was rich all over, idling at 12.5 AFR, cruise at 13AFR, WOT at 11 AFR. First thing is to turn the carb upside down and square up the Transition slot opening as seen from the bottom below the throttle plate, do the primary and secondary. Then I jetted down from the stock 74P/80S jets to 72P/76S. Upsized the squirters from stock 31/31 to 37F/35R, switched the stock pink accel pump cam for a green pump cam. Upsizing the squirters and using a longer duration pump cam eliminated the off idle hesitation it was having.
Now the fun part, tuning the carb - The engine idled too low at 600 RPM with the transition slots squared up, and smoothest at very rich 12.5 AFR. I opened the secondary side throttle blades slightly to get the idle to come up. Secondary mixture screws were out less than 1/4 turn, poor control of the AFR on the secondary side. I put .017" wires in the secondary side Idle Feed Restrictions. That gave me some control over the idle mixture screws on the secondary side, out 3/4 turn now. Opened the primary side throttle blades about 1/4 turn of the idle speed screw. Idling now at 13.5 AFR about 800RPM. Cruise at low speed in the 16AFR range, light acceleration in the 13.5AFR range, WOT in the low 12 AFR range.
The distributer tune- Vacuum advance disco and plugged. When I started, the base timing was at 10° BTDC, mechanical advance at 35° all in by 1500, just Awful. Removed distributor and took out the mechanical advance plate. Welded up the outer ends of the slots about an 1/8". Ground smooth and cleaned. Put a slightly stiffer spring on the "light spring" weight. Adjusted the slot opening by grinding out some of the weld until I achieved about 24° base and 34° total. All in now about 2500 RPM. With vacuum advance reconnected full advance is now at 40° total at cruise.
It runs awesome! Very lean at cruise in the 15 to sometimes high 16 AFR range, should be easy on gas for a big block. Richens up nicely in the 13 AFR range for light acceleration, and safely rich in the low 12 AFR range to **** and get full throttle.
