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No ported vacuum on Holley carb

I'm having a problem with a carb I bought used and rebuilt. (Yes, I used a Holley rebuild kit.) It's a Holley 4160 (750 CFM, vacuum secondary), List #3310-2, with #2726 stamped below the list number on the air horn. The problem I'm having is that the vacuum port on the side of the primary metering block, which is normally supposed to be "ported" vacuum for the distributor's vacuum advance, is in fact manifold vacuum. I checked with my vacuum gauge - it reads about 18" of vacuum at idle and drops when you goose the throttle, which is the opposite of what you want for the distributor vac. advance. Other than this, the carb seems fine. Interestingly, this is the ONLY vacuum port on the entire carb, there are NONE on the throttle plate (which would be manifold vacuum anyway). I took it apart again and followed the passage from the port, through the metering block, and it goes right to a hole in the body that comes out on the bottom of the carb, below the throttle plates. Do you think the carb has the wrong metering block, or the wrong gasket, or is this normal for this carb? If this is the case, I guess I'm screwed for vac. advance. I'd like to be able to have ported vacuum for my distrubutor (which I realize is a whole 'nother discussion, based on my newsgroup reading!) If it helps, the numbers on the metering block are: L33102 5271 5275.

Thanks for your help, Dave '72 RS Z28

Reply to
David Salerno
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some how you have gone and screwed that up. that is ported vacuum on the 3310-2, or it WAS before your rebuild. Time to start over.

Reply to
Im Right

Thanks for the reply, but that's not the case. As you know, there is only one metering block on this carb, and it only goes on one way. It's virtually impossible to put it on backwards or upside down (besides that fact that that would be plainly obvious to anyone who has ever worked on a Holley before). The passage in the casting is plainly visible, and it clearly lines up with a hole in the carb body that goes right to the base, below the throttle plates. I have read at least one other post from a guy with a 3310 who described the exact same problem (maybe he sold it to me!). At first I thought that maybe I got the wrong gasket in the rebuild kit, with a hole in the wrong place or something, but I don't see any other passage that could feed the port in the metering block. Either they made some this way, or the metering block and body (or throttle plate) are mismatched.

Dave

Reply to
David Salerno

If there is only one port and it is below the throttle plate, then it can only be manifold vacuum.

But whats the big deal. Once the throttle plate is slightly open, ported vacuum and manifold vacuum are the same thing. Having manifold vacuum at the distributor will probably make your engine idle better.

Reply to
Big Dav160

Not at part throttle they're not!

Having manifold vacuum at the

Oh it will idle fine with or without the extra advance, and no doubt the idle speed will increase with it, but that's not what the vacuum advance is for. It's purpose is to eliminate the bog you would get when you first dip into the throttle. Once the RPM's have climbed, the mechanical advance takes over. After reading literally dozens of posts on this subject in various news groups, I'm amazed at how many people don't get this, and connect their distributors to manifold vacuum rather than ported vacuum. There's a reason the designers provided ported vacuum (in most cases anyway ;-) and connected the distributor to it. If you use manifold vacuum, you will have way more advance than you need at idle, and it will drop when you dip into the throttle, which is not what you want to happen. It's true that at WOT they are essentially the same, but that's a different condition, and the mechanical advance has usually kicked in by then.

Reply to
David Salerno

David:

Aren't you the guy with the '78 T/A in England????

I think I remember helping you once or twice. Nice to see you again.

Joe--ASE Certified Parts Specialist & 10th Ann.Club Tech Director '80 Carousel Red Turbo T/A, 26k orig. '79 "Y89" 400/4 speed 10th Ann. T/A, 57k orig '84 Olds 88 Royale Bgm 2 dr, 307 "Rocket" (lol), 141k and still going.... '80 T/A project car...

Reply to
Bigjfig

That's right, I am still at it. Every time I do one job I find 2 more!

Reply to
David Toft

Such is the world of old F bodies and getting them back into stellar shape. LOL.

It's cool to see our cars abroad. I used to help a guy in Belgium that posted on this board...

Joe--ASE Certified Parts Specialist & 10th Ann.Club Tech Director '80 Carousel Red Turbo T/A, 26k orig. '79 "Y89" 400/4 speed 10th Ann. T/A, 57k orig '84 Olds 88 Royale Bgm 2 dr, 307 "Rocket" (lol), 141k and still going.... '80 T/A project car...

Reply to
Bigjfig

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