Tuning advise please! 429 stumbling (Full Version)

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Tuning advise please! 429 stumbling

tarafied1 -> Tuning advise please! 429 stumbling (5/5/2008 7:16:49 PM)
Hey guys, Need some help. I have a 67 in which I have stuffed a 1970 429. It has a Holley 770 Street Avenger carb, stock fuel pump, Performer 460 intake, cam grind (•Dur. @.050” lift = 218/228 advertised duration 276/286, gross valve lift .509”), TRW 10.5:1 pistons, Accel Blueprint electronic ignition distributor (I converted the ignition to Ford 70's style ignition), Ford Motorsport 8mm wires, MSD cap and rotor, Busch platnum plugs. I have custome headers with equal length 2" primararys into a 3.5" collector and 3" exhaust into Flowmasters with no tail pipes yet. So it is pretty mild... Timing is set at 14 degrees BTC with about 30 total. Carb is out of the box, no jet changes. My vacuum gauge isn't working but it does have vacuum, C6 trans shifts okay so I assume vacuum is pretty good. I have just started driving it regularly since the weather has been nice. Prior to this year the car was just driven onto a trailer or around the driveway. My problem, the car starts and idles fine, small lope. When I drive "normal" the car has an intermitten miss or stumble. Sometimes it backfires in the exhaust (popping sound) and seams to come and go. When I stomp on it, it runs great. It pulls hard, it will smoke the tires all day long! At 60 or 70 mph just cruzing, I can hear it miss once in a while. When I pull the plugs, they are a white to tan color. I'm wondering if it is running lean? Do you guys think its a carb issue or ignition? Seams to me to be the carb. I have 6psi of fuel pressure at idle and it runs strong under load so I don't think it's a fuel delivery issue. Any help would be greatly appreceiated. Thanks Craig

LCC -> RE: Tuning advise please! 429 stumbling (5/5/2008 7:30:27 PM)
I would try talking a couple of degrees off the total and see if the plugs get better. As fo the popping, something to do with the pick-up or a bad wire. Start buy getting one new plug wire and replace one at a time when testing. I'm assuming that you ran a new power wire to your new distributer, check the ground strap on the engine to the car to make sure its good and solid.. next....

valley firearms -> RE: Tuning advise please! 429 stumbling (5/5/2008 7:57:49 PM)
I too was thinking bad plug wire. Sounds like you have plenty of fuel psi.

67mustang302 -> RE: Tuning advise please! 429 stumbling (5/5/2008 11:23:05 PM)
Ignition problem maybe, possibly fuel ratio with the carb, might need to be rejetted. The plugs should be a light grey to tan color on the insulator, and there should also be a mark on the ground strap of the electrode that indicates total timing. Under full power it should produce a mark that's right around the apex of the curve in the ground strap. What's your timing at?

67 evil eleanor -> RE: Tuning advise please! 429 stumbling (5/6/2008 4:09:59 AM)
Check the plugs also. More than likely its in the ignition system and will be a simple fix. A scan will find the problem really quick if its a wire or plug. You can move the timing a couple of degrees also first to see it it helps.

kalli -> RE: Tuning advise please! 429 stumbling (5/6/2008 7:59:23 AM)
do you have vacuum advance connected? if you do make sure it's hooked up to ported vacuum, not manifold. It's just a wild guess, but easy way to find out is to check oin timing on idle. The ignition advance should roughly be the same with vacuum advance connected and disconnected (low or no vacuum at idle). If you plug in your vacuum advance and the timing advances a lot you might have used the wrong port on the carb Kalli

tarafied1 -> RE: Tuning advise please! 429 stumbling (5/8/2008 10:00:43 AM)
Thanks guys for the help... quote: ORIGINAL: 67mustang302 Ignition problem maybe, possibly fuel ratio with the carb, might need to be rejetted. The plugs should be a light grey to tan color on the insulator, and there should also be a mark on the ground strap of the electrode that indicates total timing. Under full power it should produce a mark that's right around the apex of the curve in the ground strap. What's your timing at? I'm not sure what you mean about the mark on the plug... I do have vacuum advance, it is in the correct port. Timing is at 14 degrees BTC and about 30 total. I have have used new wires to the distributor and I have two ground starps on the engine since the battery is in the trunk and grounded at the body. I've driven it some more and plugs get black at idle but white/tan when driven hard and shut off to check them. I do think I may have found the issue. The plug wires go thru a wire loom that seams to pull a little tension on the shorter ones at the plugs, I think they may be pulling loose over time. Thanks again for the help.

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