Which Recipe Best For My Setup?

[77cruiser]

I'd check it over carefully.  Some companies to some additional "butchering" during the remanufacturing process, like clipping/cutting the post off the bottom of the power piston......

Why do they do that, any reason you know of?

[Cliff Ruggles]

The factory used the APT system to fine tune each carb for a specific application.

Companies that "remanufacture" carburetors are building them as a "generic" unit to fit a broad range of applications.  That is why they block off the bypass air and alter the factory calibrations.  Doing so allows them to fit many more set-ups and their calibrations are often pretty "fat" so they don't get as many "come-backs"......

[Tinkerman]

Wanted to say thanks for everyone's time and especially Cliff for taking the time to speak with me and help me get a good start on tuning my carb.

As a quick re-cap, here is how the Pace Car will be setup:

- Bored 0.030 over to 355 cubic inches
- 10.25:1 compression ratio
- Quench will be 0.030" +/- 0.005"
- Original exhaust manifolds with new OEM exhaust system
- Original 041 heads and cast iron intake
- Original rebuilt distributor using Delco Remy points
- AC Delco R45 spark plugs (a little hotter than original R43 plugs)
- Will be using 93 octane pure gas

I am installing a retrofit hydraulic roller camshaft with the following specs:
- Stage 3 cam profile
- Duration at 0.050" is 215 Intake/230 Exhaust
- Advertised duration is 284 Intake and 310 Exhaust
- Valve lift is 0.470" Intake and 0.480" Exhaust using a 1.5 rocker ratio
- LSA is 110.
- Power range is 1700-5500 RPM

I figure around 12-14" Hg at idle. Based on having a lower idle vacuum, I will try the below recipe on the carb:

- Idle Tube: 0.038
- Idle Down Restriction: 0.052
- Lower Idle Air Bleed: 0.070
- Upper Idle Air Bleed (Main Casting): 0.077
- Accelerator Pump Discharge Holes: 0.027
- Main Air Bleed (Main Body): 0.070
- Main Air Bleed (Air Horn): 0.070
- Main Jet: 72
- Primary Metering Rod: 42B
- Fuel Inlet Seat: 0.135
- Float Level: 1/4"
- Secondary POE Well: 0.035
- Secondary Tube: 0.036
- Secondary Hanger: "B"
- Secondary Rods: "AX"
- Idle Bypass Air: 0.075
- Idle Mix Screws: 0.095

Once we get the engine on the dyno, I will see where in the A/F curve I may need to make adjustments.

Thanks again,
Dan

[Tinkerman]

a

[Cliff Ruggles]

What size were the upper and lower IAB's when you took the carb apart?

What size MAB's?

Did they clip the post off the power piston or is it still there?

[Tinkerman]

What size were the upper and lower IAB's when you took the carb apart?

What size MAB's?

Did they clip the post off the power piston or is it still there?

Upper Idle Air Bleed was 0.077". It was that size at the start. Lower Idle Air Bleed was 0.050".

The Main Air Bleed (Main Body) was 0.050" and the Main Air Bleed (Air Horn) was 0.050".

I am not sure what you mean by the power piston post. I think the power piston (accelerator pump?) is fully operation to include the external vent used in 1969.

Thanks,
Dan

[tayto]

why run a hotter plug? i thought that as you increase compression you should run a colder plug?

[Cliff Ruggles]

The power piston has a metal post sticking out of the bottom of it.  That is part of the APT system and adjusted via a screw in the baseplate.

I would have left the LIAB at .050" since the upper is at .077".  Opening up the LIAB with a large UIAB kills the signal to the idle tubes requiring larger ones and you may have to open up the DCR's as well.

I would have also left the MAB's at .050" at both locations and used something closer to the original calibration.  Pretty sure that carb was .067" for main jets and 42B rods.  The rods were raised to the optimum point using the APT.

Another good idea is to remove the APT screw from the baseplate.  I make a custom external screw in the lathe.  This will provide full control of the part throttle A/F once the carb is placed in service without having to take it apart and changer metering rods......