Primary or not

[classical glass]

I have a ERA with a 427 side oiler w/2 600 Holley carbs.After reading all the threads on carburators I,m confused on which carb is which. On my car the rear carb (closest to the firewall) is the primary one not the front. Could this be? While I have your attention both carbs have idle speed screws, which one should I use for my main idle speed?

[Gaz64]

Yes, the rear carb is the primary carb, since the primary barrels are closest to the centre of the engine.

The rear carb moves first, (as the primary), then the front carb moves with the interconnecting progressive linkage.

The rear carb should be used for final idle speed. The front carb can be adjusted for near 50% total airflow. Your own personal preference will dictate this choice.

Gary

[classical glass]

Thanks Gary, that says it all.

[blykins]

The front carb is still the front carb, it's just turned around backwards.

The front carb on an FE 2x4 setup is directly looked to the throttle linkage. The rear carb has the progressive slot. If you'll also notice, the rear carb has the linkage pivot lower than the front carb. This allows the rear carb to catch up quickly.

Here's how the linkage should appear:

[blykins]

Another view with another engine:

[Gaz64]

Thanks Blykins, pictures tell a 1000 words.

What was I thinking? Had wrong engine on the brain.

Apologies to all.

Gary

[blykins]

No worries....leave it to Ford to put carbs on backwards and cause logic issues....LOL

[DanEC]

When I started my ERA a few years ago I asked a similar question regarding idle tuning on my dual quad 428. It was recommended to close the primary blades on both carbs and open them equal turns of the curb idle screw to a rough-set idle speed. Then set the idle mixture in both carbs, which requires a bunch of back and forth but isn't overly difficult. A vacuum gage or a tach can be used for this depending on which you prefer to work with. After a couple of rounds it will probably be close and further minute adjustments probably won't make much difference. Once the idle mixture was set and balanced between the two carbs for the highest vacuum or rpm, then make equal adjustments to the curb idle screw so that both carbs are equally contributing to the desired idle.

Can't swear this is what Ford intended or the best approach but I've been using it and it seems to work fine on my FE. Now I've been helping a friend get his 69 Hemi Roadrunner going and it has original Carters on it and the front one (secondary carb in this case) doesn't even have idle screws and I therefore guess an idle circuit. But if both of your carbs have primary idle circuits, IMO they both need to be adjusted for mixture and idle speed.

[DanEC]

Duplicate response ??