pltmgr

This issue is also posted on C3 Tech.

1968 BB NOM 3x2. Idle and off idle performance poor. carbs rebuilt, ignition good. Cant find any vacuum leaks. When cupping hand over outer carbs at idle, air flow is significantly higher for rear carb. With engine off, carb cleaner sprayed on throttles pools in front carb but immediately drains in rear carb. This is with return linkage disconnected and throttle held tightly closed by hand.

There are a number of Pontiac 3x2 guys that advocate using throttle sealer on the outer carbs and some say the factory used a sealer for the outer carbs. Any truth to this? Thanks

wombvette

You have to balance the ends. Then set the linkages to the center. The ends are essentially completely closed at idle. All of the idle and initial off idle is controlled by the center.

gofastvette

theres more to these fancy cars then going out and buying a Rolex or bench racing at the local cruise

toms silver 60

Don't know zip about those big Holley setups, but most if not all Rochester tri power end carbs should have zero air going through them at idle. The end carbs often have thicker butterflies with different angles than the center carbs to insure a tight seal. Per Charlie Price of Vintage Speed, who works on 57-58 and GTO Pontiac carbs as well. (GTO carbs are larger) The end carbs also have no enrichment valves.

Once you get it right, you'll love it!

JohnZ

Here's the linkage adjustment procedure (not in the Shop Manual), and how the system works; also make sure you have the correct carb-to-manifold gaskets and they're installed correctly (they go one way up under the end carbs, and the other way up under the center carb - marked on the gaskets).

toms silver 60

Good to hear from an expert! Looks like there is an idle ciruit on a Holley end carb.

rongold

There is, but the only reason it's there is to keep the gas from going stale in the end carbs in case you're chicken and don't punch it !!! It is totally non adjustable.

pltmgr

Regarding pic of gaskets, is the front of the carb at the top of the pic or the bottom. thanks

SupremeDeluxe

The outboard carbs are fully closed at idle. The reason for the adjustment procedure is so that both outboard carbs will close fully without binding. When following the procedure properly, the pivot pin will reside slightly above the bottom of the arc slot in the center carb linkage.