70 Buick carb with APT?

[ponchoguy]

How does the APT work in the 70 Buick carb? Same principle and results as the 76-up APT system? Less effective, more effective? Carb # is a 7040242, it's going on a 74 400 Pontiac with mildy ported heads and a Summit 2800 cam with std manifolds. Suggestions for primary rods, sec rods, hanger and jets to start?

[omaha]

As far as I can remember; works similar to the newer style in that it positions the rods at a point within a certain range of adjustability.
This is only when the engine is at higher vacuum signals (rods are "down" in the jets) eg; idle and cruise etc. Therefore it is a very good tool for fine tuning in these parameters of engine operation.
The big difference is the design of the actual adjustment. THis will be located in the baseplate of the carb under a plug between the two idle screws. The only bad thing is that sometimes the actual adjustment screw for the adjustment will be frozen in its threads and a certain percentage of them (40%??) will break
or the threads might strip out.  However, if you can manage to get the plug out and get the screw to work, it can be a very useful tuning tool.
The screw    has a strange shaped end on it (kind of rounded/egg shaped) that contacts a little tang(?) that I believe is made of spring steel. This in turn pushes up on the bottom of the piston and positions the rods during the idle and other high vacuum conditions.
   I would go for the "first recipe" in Cliff's book if you can. this would be a good starting point as far as rods/jets. THis is a guess as I am not familiar with that summit cam.  ENJOY!!

[Cliff Ruggles]

The early Buick carbs are small main airbleed, and used "B" series rods with the APT feature.

I'd keep the jets and rods stock, and the MAB sizes as well.  Install one of our external APT screws, and a complete rebuild kit with upgraded components.

I would also get a set of our .044" secondary metering rods, and new primary pull-off if the old one is defective......Cliff

[ponchoguy]

The .044 primary rods sound good... the secondary look really really lean... what should they be from the factory? Also the 68 jets sound lean too, but with small air bleeds, guess you don't need much fuel.
Idle air tubes just need to be cleaned and pulled, no going bigger?
What is the P/N of the APT screw for the 70 carb? I will order one soon as I get paid.

[Cliff Ruggles]

Correct, the small MAB's are designed to work with the smaller .068" main jets.   Leave the stock parts in the primary side, and installed our .044" secondary metering rods.

Best to call with parts orders, the APT screw is a custom part, we don't have it on the website.  I'd also upgrade the carb with one of our rebuild kits.  The components are designed for this new fuel, and the kit will come with the correct high flow viton needle/seat assembly, and complete accl pump assembly with new springs.....Cliff