I am trying to decide what to do about the tuning on my Slant Six. I have a mildy modified SL6(see below) and I am running 89 Octane gas and a recurved distributor.
Here are the symptoms:

The tailpipe has some black soot on the tip. The plugs are white (not overly white) and the throttle response is not as crisp as I would like. It has a bog when you starting pushing on the gas, but as you continue to push on the gas it comes alive. It has a slight ping in 3rd gear under moderate acceleration. It seems this points to a problem in the transition slot/idle. I need some guidance.


bwhitejr

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'72 Duster (Performance 360)
'83 Ramcharger (Performance 318)
'80 TrailDuster (360)
'80 D-150 Truck (See Below)
CompCams 252S, Holley 390cfm, Offy manifold
Ported, Polished and Gasket Matched
P4286813 Springs,0.040 Overbore,
0.090 Shaved Head

your ping in 3rd sounds like the vacuum advance needs adjustment. try test driving with it unhooked. if it goes away it's the advance, if not, try backing down the ignition timing (where is it now?) to fix the advance, you'll need an allen wrench (3/16" i think) and slide the long end thru the hose nipple on the can. i think i'd start by turning it counterclockwise a quarter of a turn and drive it. keep adjusting/driving until the ping goes away. don't worry, you're not taking away advance, just slowing it by increasing the spring tension against the vacuum diaphragm.
as far as the carb, is this a vacuum secondary unit? maybe you need a stiffer spring in the diaphragm. is the accelerator pump working? you questioned the idle slot. does it idle ok? do you have the throttle plates closed enough to allow the idle circuit to work? you'll know you don't if the mixture screws do nothing when turned or if you have vacuum at the advance port all the time. i wonder if the power valve is wrong as they tend to be a problem area. i don't play with holleys anymore, but here is a good resource if you don't have a book on them. http://www.holley.com/data/TechService/ ... valves.pdf
hope some of this helps.

-james

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The initial timing is 12 deg BTDC. I looked at the butterflies and they look closed at idle. The idle is OK, but is slightly rough (inconsistent).

bwhitejr

_________________
'72 Duster (Performance 360)
'83 Ramcharger (Performance 318)
'80 TrailDuster (360)
'80 D-150 Truck (See Below)
CompCams 252S, Holley 390cfm, Offy manifold
Ported, Polished and Gasket Matched
P4286813 Springs,0.040 Overbore,
0.090 Shaved Head

I forgot to mention I am getting high 14's to low 15's MPG. This is a truck, so can I expect better?

BTW it is vacuum secondaries 4160 (0-8007).


bwhitejr

_________________
'72 Duster (Performance 360)
'83 Ramcharger (Performance 318)
'80 TrailDuster (360)
'80 D-150 Truck (See Below)
CompCams 252S, Holley 390cfm, Offy manifold
Ported, Polished and Gasket Matched
P4286813 Springs,0.040 Overbore,
0.090 Shaved Head

bwhitejr-
if you don't have much experience with holleys then i'd suggest you buy a good book on tuning them. i think your 390 just isn't set up properly. just learn a little about it and start playing around one step at a time. i personally gave up on holleys a long time ago, though i still have a couple laying around and the pair on my valiant will give way to a set of BBSs sometime soon. i know there are a few members on the board who are running them, but can't remember who.

-james

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Transition/idle Throttle plate should not close past transfer slot at curb idle. A small portion of slot should be visable under plate. If not there will be off idle flat spot.On the other hand more than about 0.040 inch opening will result in a rich idle and off idle flat spot. Remove carb turn over and see how plate relates to slot. While its off check secondary throttle plate opening.Depending on which condition exits in primary you need more or less opening. Holleys have four corner idle so do not close it completly. One of my old books says turn adjustment screw 1/4 turn from closed position. For explantion too much opening in secondary results in too much air on secondary side.Forces you too back out curb idle too much to get slow idle.Primary plate drops too low closes off idle slot.Old books I could copy some things .Send in mail Ill pm