Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor

looking for some better mpg/setup advice needed

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mike mc:
first, a little info 1999 single cab s10 3600lb.
1985 West coast engines stage 1 350 bored .30 over, stock pistons,  stock heads,  204/214-272-284 melling cam .420 lift 112 separation
edelbrock rpm manifold,  hei with full upgrades,15 initial,19 mechanical, 16 vacuum.  short kit headers, 2.25" to flowmaster scavenger y, 3"out to dynomax bullet.  patc 700r4 trans 1800 lockup stall converter. 4.10 gears.295-50-15 tires 27" tall.
the carb is a 17088041 800 cfm. this carb is an oddball, it is almost identical to a 17085213. I think the jets are .76, the primary rods are marked 61s, I am not sure what size they really are, I need to open it back up the apt is set at 1.25 off bottom it has a j hanger and EK secondary rods the power piston spring is stock, probably old. the piston changes position when the vacuum drops to 7 hg. I am getting 15 to 16 mpg but I could use a little better mpg. considering I drive 80 miles a day. any rod jet hanger or spring recommendation would be appreciated.

Cliff Ruggles:
Sounds like a big block Chevy motorhome carb.  They used a very generous fuel curve, most had 75 main jets teamed up with full tapered .060" primary metering rods with .036" tips.

Use the APT system to fine tune part throttle A/F for best fuel economy, and 73 or 74 main jets would be PLENTY for what you are doing.....Cliff

mike mc:
I also forgot to mention the idle air screws are turned out 5.25 turns. I think I need to drill them out to .086. also do you thing the power piston spring is allowing the piston to move at the right hg of vacuum. I also run a wideband o2. cruise is 13.5, at full throttle it goes to 10.0.  also at cruise my vacuum is 14 to 16 hg.

429bbf:
what does that have for compression . im thinking 8.0 someone correct me if im wrong. i have gotten 4mpg better on a bbford by raising the comp. to appox 9.5 . i dont think you can burn the gas properly. im shooting for 10.2 on the next one will see how that does. should know in a few months . i run all qjets on my ford and get excellent milage and power. fwiw

mike mc:
it is probably 8.0, I know I would get better mpg if I would swap for a set of vortec heads and d dish pistons. but right now the motor is still under warranty, and I still want to dial the carb in as close as I can get it.

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