I am going to switch (try out) a carb on the motor to see if all my problems lies with the EFI. Could someone explain the difference to me with vac. secondaries, mech, secondaries and double pumpers? I hear the terms but have a vague idea what the differences are.

 

A mechanical secondary carb has the secondary throttle blades opened directly by the throttle linkage. To prevent bogging due to suddenly going lean as the secondaries are opened before air begins to flow through them, a second accelerator pump is used, which leads to mechanical secondary carbs also being known as "double pumpers". If the carb is sized too large for the engine, it can take a substantial secondary pump shot to prevent bogging, so double pumpers have a reputation for low mileage.

Vacuum secondary carbs have the secondary throttle blades opened by venturi vacuum once the demand from the engine starts drawing enough flow through the carb. An over-sized vacuum secondary carb will open the secondaries later, or won't allow the secondaries to fully open. In effect, the VS carb "sizes" itself to the needs of the engine to an extent, and they have a reputation for getting better mileage than double pumpers.

There's another broad family of carbs that don't have as well-known a name, the "air valve" or "demand" secondary carbs, like the Quadrajet, Edelbrock Performer and Thunder series, and the Carter AFB, AVS and Thermoquad. In all these carbs, the secondary throttle blades are opened directly by the throttle linkage as in a mechanical secondary carb, but an air valve above the secondaries is balanced by a counterweight (AFB and Performer) or a spring (Quadrajet, Thunder, AVS and Thermoquad) doesn't open until the demand of the engine requires it, somewhat similarly to a VS carb.

There are also variable venturi carbs, like the Predator and the SU and such, but they're not very common on our sorts of applications.

 

That answer was so good, it's been added to the carb sticky. https://www.thirdgen.org/forums/carb...rd-please.html

 

Yea that was very informative. Thanks! I'll have more I'm sure I bring to the table.

 

Heres another...Do the primaries always point to the front of the car?

I'm probably getting a Demon and need to make the fuel feed lines on the drivers side pointing to the rear...Not on the pass side pointing to the front.

 

Yes, the primaries are at the front.

Why do you need the fuel inlet on a particular side?

 

The way I did the braided lines for the HSR will keep the AFPR on the drivers side in the rear and being able to face the carb feed line towards the rear on the drivers side would keep my engine bay clutter free (what I'm all about) and eliminate a 180 degree fitting from the carb feed line.

I know the Dominator style bowls let you plumb ono either side but was unsure about the Speed Demon's and didn't find it on their site anywhere.