dual fours tuning info needed

Hi guys,
This is my first post and I'm kinda hoping someone can offer advice, or at least point me in the right direction. I've got a 302 Ford with a low rise, dual plane manifold with a pair of 390 vacuum secondary Holleys. The engine has a Comp Cams 268XE cam, and 351W heads but is mostly stock. I've got the engine running, and am happy with the throttle response, but the idle quality is not what I'd hoped, so I need some help making sure the carbs are as good as they can be. I've done a search, but found mostly general advice, I'm hoping for some step-by-step advice. Anyone feel generous today? Thanks!, Jim

 

What exactly do you mean by idle quality?


Mutt

 

A couple of things come to mind.

First of all, what he said. ^

Second, that particular cam is going to have something of an "idle" in a 302. Are you having problems even getting it to idle without cranking up the idle speed, and/or are the idle screws not having much effect?

Third, if so, you may want to slightly open the secondaries a little, on one or both carbs, depending. You can do this on the small set screw on the right side of the carbs by the secondaries. You'll need to either pull 'em to do this, or, take a pocket screwdriver & cut it down to fit (they adjust from the bottom side). If the carbs are older, the screw may not turn easily & you'll have to pull the carbs.

Fourth, I'd recommend getting a decent carb book, it makes life easier & gives some "in order" procedures, so you don't end up bouncing all over the place & doing some things three times. Holley Tuning & Modifying by Jeff Williams isn't bad, though a little old.

 

Thanks guys, I guess I should've been more clear. I don't really mind a rowdy idle, but when I turn the idle screws to try to lower the idle, it dies. This weekend I intend to disconnect the linkage so I'm sure it's not affecting the idle, then start the motor and adjust each carb seperately. I have a vacuum guage so my plan is to try to get an equal reading at the base of each carb, then reset the idle speed. The carbs are new 390's so they've never been on a motor before. I've heard about opening the secondaries, but how do I know if I should try it? I thought that was only for cams with lots of overlap, but I'd sure give it a try if it'll help. I have an older Holley book, but as usual it barely gives any tuning advice for multiple carbs. The only advice they give is to stay away from mulitple carbs for the street, and that ain't going to happen!