Quadrajet running lean after head and cam swap

[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

[bcarlson78248]

Cliff - called today, but they told me you wouldn't be in until tomorrow, so I will call tomorrow morning.

Thanks,

Bruce

Repeating the engine and carburetor info.
Engine upgrades in July 2018
- Blueprint aluminum 195cc heads, 2.02 intake, 1.60 exhaust, 64cc chambers
- .026 Mehle head gaskets to increase compression to ~ 9.4 compression ratio
- Edelbrock dual plane intake
- Howards roller cam 213/217 @ .050, 112 LSA, lift 0.485 int/0.495 exh
- AC delco 41-629 plugs, gapped at .040
- Cast iron manifolds and full duals
- TH350 with stock converter, 4.10 gears, 31" tires
- Truck weight ~ 4800-5000 lbs
- Quadrajet (17080213 Q243 CPX)

Timing
- Initial timing 12 degrees BTDC
- Centrifugal adds 20 degrees by 2200 rpm
- Vacuum advance adds 17 degrees
 
Current Quadrajet setup
- Quadrajet (17080213 Q243 CPX)
float - 1/4"
Power Piston Spring - dark blue
Jets #73 (stock)
Primary rods - unknown
Secondary hanger - G,  33797  .545", 2nd shortest
Secondary rods - DP, - leanest (686)
Accelerator pump - 2nd hole

[Cliff Ruggles]

We got in late yesterday, took a long weekend to go to a wedding out of town.  Will be in the shop the rest of the day.......Cliff

[bcarlson78248]

Cliff,

I was out of town, so I just got back and opened the parts package you sent for my Quadrajet - 17080213 Q243 CPX.  Now I've got it apart and am installing the parts you sent.

I have quite a few questions, so please bear with me.

- Jets are #74 vs. the original #73, so a little bigger.
- I removed one of the idle air bleeds and found that it measured .032, but the new ones you sent are .030.  I expected them to be bigger, maybe as much as .037.  Did I get the right ones?  Or should I just drill these out a little bigger?

- Power piston is orange/red vice the dark blue I had before. Which spring do you think will work better?  It looks like  moving to the orange spring would make sense for smoothing out the power transition.  However, I still get about 19" of vacuum at idle with this 213/217 @ .050, 112 LSA cam. 

- I set the APT 2 1/2 turns out for now.  Any suggestions about whether this should be changed?

- New Secondary rods are DA (.0440 tip), originals were DP
- Primary rods are:
old ones measure at .049, tapering to .034,marked 49Y
new ones measure at .050, tapering to .038 (marked as 50C). 
Would I be better off leaving the old ones in for a stronger power mode, or would it get too rich in power mode when combined with the #74 jets?

I've got the float set at 1/4" right now.  Any reason to change?

Thanks for your help.  I appreciate any input you have.

Bruce

[Cliff Ruggles]

Removing airbleeds at .032"?  Hoping you are referring to the idle tubes.

Yes, we don't pre-drill the idle tubes unless requested, so open them up some.

This will bring in more fuel to idle, off idle and transition.  It also feeds the main system.

Use the jets, metering rods and PP spring provided with the larger idle tubes and make sure the DCR's are at least .055".

Do some testing, use the APT system to fine tune, and see where things are at......Cliff

[bcarlson78248]

My error - new idle tubes measured at .030, so I will drill them out to .037.

DCR - i

[bcarlson78248]

When I replied with my phone it cut off the end of my message.

Question - What is DCR - is it the idle down channel restriction?
I measured the idle down channel and its about .051-.052, so it looks like I need to drill it out to .055 (my .050 drill bit fit loosely, but the .052 bit won't quite make it.)

Is there any trick to drilling the idle down channel larger?  The fittings appear to be made of brass and pressed into the carburetor.  If I drill them from the top I can't see where the filings go or how to ensure the filings are flushed out.

Thanks,

Bruce

[77cruiser]

With the base off just blow the channels out with air. The channel is fairly large so it will clean out.

[bcarlson78248]

I've continue to work on the carburetor and have these setting/specs so far. 

The only question I have now is whether I need to make any changes to open up the lower idle air bleed or reduce idle bypass air.   
Idle bypass air is larger than expected, but I've also converted to an electric choke. 

Idle air tube - opened to .038
DCR - opened up to .055
Upper idle air bleed - .052 stock (in air horn)
Lower idle air bleed - .0625 stock
Idle bypass air - stock was about .105 (larger than expected)
Mixture screw hole - opened up to .078
Plate holes - none
APT - currently 3 1/2 turns out
I also notched the secondary air flaps so that the fuel holes were exposed to the underside of the flaps.

Thanks,

Brucee

[77cruiser]

Don't open the idle bleed, looks like you should be rich enough now.

[Cliff Ruggles]

The upper idle airbleed is in the main casting just above the DCR's, not in the airhorn.  It's probably around .070".  No need to modify any airbleeds at this time.

The idle tubes are also fuel supply, not air.......Cliff