Always timing, then carb. I'd put a $20 down that this approach will find and fix the problem.
engine flattens out
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engine flattens out
My 68' 427 flattens out at about 5,000 RPM. It pulls real hard to this point and then it seems to hit the wall. It does'nt do this every time, but even once is to often. Timing is at 15 degrees advanced. My vacum advance is adjustable, do I need to look at that or something else?
Team Owner
Joined: Jan 2006
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From: Crossville TN
Are you certain that the carb is opening completely when you push the accelerator to the floor? [exercising it with your hand under the hood doesn't verify that your 'foot' is doing the same thing]
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From: At my Bar drinking and wrenching in Lafayette Colorado
First, initial timing is irrelevant - you need to make sure you're at 36 degrees total timing for correct performance. There is no vacuum advance at WOT, so the vacuum advance unit does not come into play for your problem.
If you have 36 degrees total timing and the timing is stable at 5000 rpm, your problem is with fuel supply and mixture. Make sure you do not have any fuel filters installed in-line on the suction side of the pump. Make sure the filter you do have is new. Make sure none of the rubber fuel lines are kinked (lines between tank and frame and between frame and pump). If you have a Holley, make sure the secondary vacuum spring is correct for the application. Make sure the carb is jetted to spec. Make sure float levels are set correct. If you have a Q-Jet, make sure the seecondary airvalve spring windup is set at 3/4 turn and that the float level is at .375" with correct jetting for the carb number.
Finally, make sure you do not have an aftermarket "electronic conversion" in your stock points-type distributor and make sure the points you have are of good quality. Dwell should be at 30-31 degrees.
Lars
If you have 36 degrees total timing and the timing is stable at 5000 rpm, your problem is with fuel supply and mixture. Make sure you do not have any fuel filters installed in-line on the suction side of the pump. Make sure the filter you do have is new. Make sure none of the rubber fuel lines are kinked (lines between tank and frame and between frame and pump). If you have a Holley, make sure the secondary vacuum spring is correct for the application. Make sure the carb is jetted to spec. Make sure float levels are set correct. If you have a Q-Jet, make sure the seecondary airvalve spring windup is set at 3/4 turn and that the float level is at .375" with correct jetting for the carb number.
Finally, make sure you do not have an aftermarket "electronic conversion" in your stock points-type distributor and make sure the points you have are of good quality. Dwell should be at 30-31 degrees.
Lars
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Point "Bounce" at high RPM's is pretty common. I use Accell points which are of superior quality. (That is if you still have points),
Float level low will run you out of fuel at high RPM's.
Float level low will run you out of fuel at high RPM's.
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From: Seattle WA
St. Jude Donor '14
The carb may well be the problem...but timing is a) easier to sort out and b) less sensitive to changes. You're not really "tuning" the timing - you're setting it to work correctly and then you can focus on the more complicated tuning of the carb.
Just my $.02.
Just my $.02.
Safety Car
Joined: Mar 2007
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From: Bridgewater nj
Jagan states it happens once in awhile. If it was a timing issue it would happen all the time. I would check fuel pressure and secondaries working. Sometimes the choke is closed a tiny bit and this blocks the secondaries from opening.
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I have not noticed if the secondaries are opening. I will drive it and listen carfully. I think they are as the car is really pulling hard to a point then it flattens out to nothing. Almost like fuel starvation.
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From: Pace FL