As some of you may recall, I've been struggling this spring with a huge idle problem since installing the XS282 cam in the 396. It didn't idle right from the start, then I compounded the problem by switching to E85 fuel.

I figured it must be something with the air bleeds, although some thought I was nuts. One suggestion was to open up the secondary blades more, which I did and didn't seem to help much. In reseaching 4-corner idle systems, I stumbled across an old Proform mainbody thread that discussed "the extra 36 air bleeds for the secondaries when using 2-corner idle". Sure enough, I didn't receive such "extras" with the mainbody, and it had 73's on all four corners.

I picked up some 36's tonight on the way home, put them in, and gave it a try - it immediately idled at 1800 RPMs, even when cold. I slowly backed off the idle speed screw as it warmed up, it was backed off all the way and still idling (smoothly) at 1300 RPMs. So, now I need to pull the carb back off again and close those secondaries down a little.

This about had me pulling my hair out, as I've had this mainbody since late '03 and never had any problems - until this past March.

Thirdgen.org strikes again!

 

excellent, i have picked up those mainbodies for my friends cars when I work on them, and it never included extra airbleeds either. Now I'll have to mention it to them, although none of them have problems with idle screws either. Must be related to that cam swap...?

 

It probably would have idled better with the old cam if the secondary idle air bleeds had been proper.

Forgot to mention, one tidbit of info that convinced me was looking at the original Holley mainbody bleeds (non-screw-in) - the primaries were big, secondaries little.

 

i've heard of people removing the air bleeds by drilling and tapping out the holes and using brass screws with a numbered drill set to make their own air bleeds and even nitrous jets this way based on the numbered drill for size. ever seen this done?

 

Heard of it (magazines), but when the speed shop had them bulk for $2.22 each, and I don't have any numbered drill bits, it didn't make any sense to try to make my own.

I picked up the pair of 36's, plus a pair of 34's and 71's, just in case, for $14.37 including tax.

 

Five- Seven I bought one of these PF main bodys but havent used it yet.
Still waiting on a replacement billet throttle plate. Using a old 700dp with a damaged base for parts. Just checked the airbleeds and they are, all 73's
thanks for the heads up on the secondary air bleed size for a 2 corner idle system. Definately have to pick up some extra air bleeds (#36)

 

So forgive me for hi-jacking...sort of, and for being ignorant...but are we talking about Holley style carbs here? The air bleedes are in the top of the airhorn? If I change mine will my 406 idle with out choking the folks behind me at a light? I have a 770 Street avanger and a 270 Comp cam. Sorta rich at idle. Sorry, I know a good bit about the engines and performance setups, but I never really played with carbs much, therefore never really learned any tricks.
I really feel like a dumb **** here, but hey ya' only learn by asking right?

 

Yes, we're talking about Holley style carbs here. However, the "standard" Holley, such as the 770 CFM Street Avenger, doesn't have screw-in air bleeds.
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I'm not quite out of the woods yet. When adjusting the secondary blades down to give the primaries more authority, it starts getting a little ragged again. I noticed when fussing with the throttle body that the idle slots in the secondaries don't quite line up the same - one wasn't cut down as far as the other (it's not the blades, they close together). So, I'll need to pull it apart again and trim that slot until it uncovers like the other one. I may have to go to the 34's as well, due to the E85.

But, it is a lot better than it was.

 

nice to hear that you have a smooth idle now.

remove the screw and insert it from the top. so you don't have to pull the carb for adjustment.

nebu.

 

I picked up a little screwdriver bit ratchet handle so I can adjust the secondary open stop without pulling the carb. I have enough room with the Air Gap and no heat shield so I can do that.

I still have to pull it off and apart again to get the secondary slots to line up with each other. It will idle by itself now, but still finds opportunities to die, so if it doesn't clean up after the slots are aligned, I'll go with the 71/34 bleeds and see how it responds to them. Between those two, it should finally idle like a "real" engine again. I'm still amazed that it idled okay in the past, and started acting up so after the cam swap.

 

Took it apart again, spent about half an hour picking at that secondary idle slot with my pocket knife - precision hand work, you know. It actually came out pretty decent.

With the 71/34 bleeds, it still acts too lean, especially on the primaries. It idles best with more secondary opening, but idles too high. Went down one more step (actually, 69/31), and it improved again. But, I'm have difficulty getting a smooth, dependable idle at an acceptable idle speed (about 1000 RPMs in drive is best I've gotten so far). Tweaking the secondary vs. primary opening is the issue, I think I'm just about there, though.

I'm probably going to jet down, since I assumed the surging I was getting at cruise was main jets, when it was probably the huge secondary idle air bleeds. It's running great, but I'm getting just a little blackening on the plug bodies. Overall, the plugs are staying pretty clean, but with the E85, they should be squeeky clean.