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Discussion Starter · #1 ·
I was changing the air filter today and when I pulled it I noticed that there are two nipples on the front of the carb that are capped off, but the caps were broken.

My initial thought was to get two new caps, but I decided to get the manuals for the carb from the edelbrock website. According to the manual, one is for "3/16” TIMED VACUUM (Distributor vacuum advance port for emissions controlled engines)" and the other is for "3/16” MANIFOLD VACUUM (Distributor vacuum advance port for non-emissions controlled engines)"

My guess is that one of these should be hooked up to something, probably the distributor. My question is what one?

The rig is an 86 RC, edelbrock performer carb and intake. The emissions goodies have been removed as far as I can tell.

Would this help out my gutless off idle problems?
 

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Is your truck still lean burn. Mine is not and I have a 600 AFB on the one on the right is capped the left is hooked up to manifold vacum i beleave its a mess under my hood. the dis is hooked to manifold vacum to I went nuts when I got the AFB tryin to get this stright eddys web site should tell you depending on what one you have 500, 600, emission 600, 750.
 

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I always thought small block distributors used timed vacuum not manifold vacuum on the distributor.
 

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It will work either way, late model emissions carbs are normally set up to idle with retarded spark timing(ported advance). Try it both ways, if you get an off-idle stumble with full vacuum advance, try it it hooked up to the ported vacuum connection. In either case, always set the timing with the advance line disconnected.
 

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Discussion Starter · #5 ·
I looked it over and saw that the vacuum line for the distributor goes into a bundle and from there I assume that it goes to a vacuum distribution point on the back side of the intake.

For the time being I just capped off both lines. Maybe next weekend I'll unhook the one on the distributor and see if I can feel if it has vacuum at idle, cap it, then try the port on the carb that I think is comparable to the one currently on the distributor.

The trouble is that my engine compartment is kind of a rats nest too, courtesy of a guy that seemed to know what to do with putting an engine together but wasn't so good at a clean installation.

How do I tell if it's lean burn? I don't think I've heard too many good things about the system, if I have it how do I eliminate it?
 

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My '86 has a temperature controlled vacuum switch(valve) on the front left side of the intake manifold, three ports one to the distributor one to manifold vacumm and the third one to the ported advance nipple. When the engine is cold the distributor is connected to the ported line. When the engine gets hot the valve switches over to full vacuum, that helps to speed up the idle to help cool things down. Pretty handy when you set the timing, pulling the connector off that valve is a lot easier than reaching over the air cleaner to reach the hose on the distributor. That bundle of hoses also supplies vacumm for the egr valve, the vacumm cannister purge circuit and the exhaust heat riser, it might be worthwhile to figure out where everything goes in case you need that stuff to work. 
 

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You don't want any vacuum advance at idle.  The port for your distributor vacuum advance should read "0" at idle and then show manifold vacuum right off of idle.  The port is blocked by the throttle plate until you press the go pedal.

Timed vacuum is there to feed in the output from float bowl or charcoal canister into the carb but not at idle.  So it opens at a slightly higher vacuum number to ensure the vehicle is under way. 

Caution above all from memory!


Cheers

Chris
 

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Yea, the dizzy vacuum you want timed (0 at idle) and on your performer it is the left nipple if looking from the front of the truck. The right is full manifold vacuum and mine pulls right near 15 in. HG if I remember correctly but that is with a larger than stock cam.
 
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