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427 FE not delivering power........?
2 Attachment(s)
Hi guys,
My aluminium FE arrived in a crate. The carb had no instructions and I’m not familiar with the QFT. I’m told it’s a 780, but not sure how to verify that as there’s no markings I can see. Anyhow to the point. The carb has two small ports (arrowed) and I’m not clear what these are supposed to be used for. When I installed it, I though best to cap them of with a couple of neoprene caps, I had lying around. Now I’m wondering if this was a mistake and is affecting the carb operation, in particular the vac secondaries. Any input I’d be very grateful as I’m not getting the power (503/532) I was told the engine produced in the dyno. Also there’s an unpleasant crackle in the exhaust note, that I’m guessing is unburnt fuel. Do get me wrong. Car has big cam idle and runs smoothly after 2000 rpm. Just feels more like 250 bhp. I’m sure the exhaust note is linked to the missing power. It’s really odd and I don’t feel I was misled by the builder. Only other clue is the MSD 6 AL2 we couldn’t get the 1st stage to work. I was going to use it as a 4000 rpm limiter, for if I gave the car to my kids to try. In the end we set both at 6000 limit. Thanks Mike |
If you have no vacuum advance on your distributor, then both of those ports should be capped. If you do have vacuum advance, then it should be connected to the lower port, which is full manifold vacuum. This will give you vacuum advance at idle, which will allow you to lower your throttle idle screw and provide a smoother idle(due to more advanced ignition timing). The top port is timed vacuum, which is an emissions port, which provides vacuum advance only at higher throttle conditions(for emission controlled engines). I suspect your problem lies elsewhere. The adjustment screw on the vacuum advance diaphragm can be turned out (CCW) to make the secondaries open sooner. Sometimes they are set for a heavier car and open too late or not at all. Also, recommend you check ignition timing to specs. The Quickfuel or Holley websites may have more info. (Holley bought out Quickfuel). Good luck.
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Also, adjust idle mixture screws on the sides of the front metering block to achieve the highest manifold vacuum at idle, usually 1 and 1/2 turns out (CCW from closed)
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Thanks Peter
Distributor is MSD 8584 Pro Billet. Pretty sure it does not have vac advance. I’m guessing somebody on this forum knows what’s up with it. |
I would confirm timing at idle and at about 3,000rpm. You want all the advance in by then. Target should be 14-18 degrees at idle and 36-38 total.
If your carb is a 780cfm then I suspect it is a vacuum secondary. Cobras are very light and unless the vacuum secondary spring has been changed, it is likely the secondarys are not opening. The standard spring is for a car that is probably 3500 pounds. I found that by putting a zip tie around the secondary shaft, I could tell if it moved. Thus indicating the secondary opened. Play with it when the engine is off and open the secondaries, you should be able to see where to attach the zip tie. Alternatively, you can zip tie the secondary shut. You would notice significant power decrease if it is working. Likely the lightest spring in the Holley pack is what you need. John |
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The 8584 is for a 351 engine. |
The msd puts out multiple sparks probably starts 10 to 15 degrees early. I would try moving the distributor to retard the timing 6 or 8 degrees and see if that helps. or you could try the timing at over 3000 rpm for total timing as the multi spark is only under 3 K then only 1 spark. 34 to 36* total depending on your octane in fuel.
Perry |
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Mike, Giving a 427 Cobra to your kids to try is almost always a bad idea ... Ed |
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If the first spark occurred early, the engine would ping. An ignition timing light picks up the first spark regardless, so sparks could not be occurring early. So to the OP, please verify your timing as mentioned above by others, with a non-dial back timing light. If the engine truly feels like 250 versus 500, there is something seriously wrong in your installation. Either the timing is retarded from where it should be, 18 - 36, or the fuel supply can't keep up. Does it go well in 1st gear, then lay down, or not at all? Gary |
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