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Old 09-24-2011, 03:29 PM
Blown496 Blown496 is offline
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blower carbs tuning (long)

Blown 496 with dual Holley 4777's. Manifold ref 6.5 PV's. I have stock carbs with quick fuel 4 corner idle blocks. .031 pvr's and 68 jets front, 80's rear. MSD6al Timing was locked at 32. Engine has always idled rough like too much timing and only smoothed out if timing is around 20 total but is really down on power. I put the advance back in the MSD so it has timing 15 idle and 32 total in at 2500. Idle at 1000rpm seems to like under 12.5 afr or it will lean to the 16's nearly die then recover when the clutch is disengaged and let off the gas. It will read same afr idle as steady cruising. Light acceleration as in passing will go in the 10's and slowly come back to what ever I set it at idle. When coasting it goes into the 11's. As I accelerate through the gears it will drop in to the 10's and rise into 11's. I can slowly open the throttle into the front jets and see it lean into 13's then the pv and jets rich it up. WOT is in the 10's. The cam is a hyd roller 114lca on 109icl. Edelbrock performer rpm heads. Blower turning 1:1. Plugs always look clean and porcelain turning light gray. I have 140lb cranking compression. It seems lazy rich off idle unloaded but drives fine. Never stumbles or spits. It just runs rough and has that trailer towing jerking except when accelerating. It does not have the power to smoke the tires at a 20mph wot. It really doesn't have much more than my blown 350 did. Idle screws out 1 turn with pcv on front carb and 1/2 turn no pcv. What am I missing here? Never had this much trouble blown or N/A in 40 years.
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