on a whim today i thought id try a little tuning on my bbd in my duster. recently it had developed a bad stutter/miss whenever i would full throttle power brake it against the converter. i tore the top off the one from my truck and pulled out the jets:120-392. the ones in the super six bbd were 120-386.

according to an edelbrock strip kit this means they were 0.092" and 0.086" in diameter. i swapped the ones from the truck to the duster and while i was there i swapped the stock step up 5 in. Hg. orange spring to a lighter 3 in. Hg. blue spring.

i always knew the car was running to lean and figured the high load stutter was caused by this.

afterwards i took the car for a small around the block drive and it definantly seems more responsive, and i also have picked up 1-2 inches of vacuume according to my gauge. my main wonder is what affect the step up spring has on tuning and driveability? i plan on taking the car to my old technical center and running it on their chassis dyno to fine tune the jets in. is it possible to modify afb/avs metering rods to work with the bbd?

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1975 Plymouth Duster,225/6 2bbl. and duels, 904, 7 1/4
1986 Dodge Charger Shelby, 2.2 Turbo I, A525

Did you change jets, or metering rods? I have played around with metering rods, and the step up cams on BBD's but never jets. Not all BBD's have the adjustable cams.

I have found my wide band Inovate O2 sensor and AF ratio gauge to be a wonderful diagnostic tool. It is mounted in the dash, and is an essential part of good tuning on the EFI Mega Squirt in my Dart. But, I see no reason why you could not, and should not use this to fine-tune a carb. It seems it would be all good. You have to have a bung welded into the exhaust a foot or so downstream from the manifold, and then there is a sending pack that must be mounted somewhere like on the frame.

Sam

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i just changed the jets. i would have liked to kept the same jet/rod size relationship on the cruise, and have more jet area to richen it up when i step on it.

unfortunatly i was limited on tuning parts and time. i like the idea of actually crunching the numbers and running a lean effective jet/rod for cruise and mileage, and a corresponding size jet/rod for power. of course this means i may have to make my own rods after i fine tune what jet will work best.

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1975 Plymouth Duster,225/6 2bbl. and duels, 904, 7 1/4
1986 Dodge Charger Shelby, 2.2 Turbo I, A525

If you keep the same jets, and raise the rods in their at rest/idle postition by adjusting the cams, you can get the same cruise mixture but come into power mixture earlier. It seems you could also have the lower part of the rods machined down to a smaller diameter to reveal more jet when rods are raised in WOT.

Consider the wide band gauge. It will open new worlds to you. They are expensive, but eliminate most of the guessing you do otherwise.

Sam

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