Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

Quadrajet running lean after head and cam swap

(1/4) > >>

bcarlson78248:
I have a Quadrajet (17080213 Q243 CPX) that I rebuilt with a Ruggles kit several years ago.  I was on my stock '75 vintage SBC 350 crate engine and worked very well.

I've now swapped to Blueprint aluminum heads, and a 213/217 @ .050 Howards cam, so I have about 9.4 (used to be about 8.2) compression, and about 20 degrees more cam duration.

I'm using 12 degrees BTDC initial, and my mechanical advance adds 20 degrees (more than I remembered). I have an Innovate wideband AFR gauge in the truck.
- Engine starts and idles well with 3 turns out.
- Under light acceleration it kind of stutters/chugs, but keeps accelerating. It looks like AFR goes up to 15-16, and sometimes higher, so its not getting enough fuel.
- Under harder acceleration it pulls more smoothly, but AFR still runs only about 14.5. IIRC, it used to run about 12 AFR as the secondaries were kicking in.

Notes from my rebuild say the jets are #73, primary rods unknown, G secondary hanger, and DP Secondary Metering Rods. Accelerator pump 2nd hole, APT 3 1/2 turns out.

Where do I start with tuning the carb for the new head/cam combo and what do I need to buy?

Thanks,

Bruce

Cliff Ruggles:
How much timing is the vacuum advance adding?

I would call the shop when you get time and we can supply tuning parts for the new combination.  I'll have to look up what that carb uses and how it was set up by the factory.  Pretty sure that one is SMAB and will use our new 50C metering rods.  They are full taper and teamed up with the right main jet will get the primary side where you need it.

You'll basically need jets, primary metering rods, secondary metering rods and a power piston spring.......Cliff

bcarlson78248:
The vacuum advance adds about 17 degrees at cruise.  I get a very stable 19" of vacuum while idling at 800 rpm, and I'm running manifold vacuum to the advance can.

I will give your shop a call and see what type of kit they can put together.  Do you have any rough estimate of the cost for everything I would need?   

Is there something I should look at to see if it is an SMAB carb?    I pulled it off of an '86 Chevy 1 ton pickup.

I also have an Edelbrock 1406 and one of their tuning kits, but in the past I could never get it running as well as the Quadrajet I rebuilt with your kit.

Thanks,

Bruce

bcarlson78248:
Just to provide a recap of engine specs before I give you a call.

Chevy SBC 350
- Blueprint aluminum 195cc heads, 2.02 intake, 1.60 exhaust
- Edelbrock dual plane intake
- 9.4 compression ratio
- Howards roller cam 213/217 @ .050, 112 LSA, lift 0.485 int/0.495 exh
- Cast iron manifolds and full duals
- TH350 with stock converter, 4.10 gears, 31" tires
- Truck weight ~ 4800-5000 lbs
- Quadrajet (17080213 Q243 CPX)

Bruce

Cliff Ruggles:
We're in the shop 8am-4pm, M-F EST.  Call volume is heavy so if we don't answer leave a good number/message and we'll call you back....tks....Cliff

Navigation

[0] Message Index

[#] Next page