At my wits end!@!
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At my wits end!@!
I just finished getting my engine back together on my truck after finding condensation in my oil and replacing head gaskets, intake gaskets, distributor (for good measure). I set my base timing correctly and re-checked it many times. My problem is that in park, everything seems great. The engine revs up and sounds beautiful, but under load when driving, I don't have any power. If I use more accellerator than just a little, it sounds like the engine is trying to work harder, but I get no rpm increase out of it. I checked to make sure that my vacuum advance on this new distributor is working, and it is. I checked compression - 120 on all cylinders, I checked dwell.. it's at 31. I don't know what else to check. Could it be carb? I replaced the carb with an Edelbrock Performer 750cfm a couple months ago, so I tend to think that I shouldn't be having any problems with that. Any ideas?
Greg
67 F100 CCS 390 FMX
Greg
67 F100 CCS 390 FMX
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At my wits end!@!
greg
it sounds to me as if your timing is not advanced far enough. Try bumping the timing a few more degrees and then go for a test drive. One other thing, why do you have such a big carb on yr truck? If it is a 360/390 a 750 is too much carb for the street. It could be that you have no power because of a weak carb venturi signal. Id say if you had a holley 500 CFM of the stock 2 barrel, put that on the engine as well. Id bet that yr problem would be solved. Try the timing first and then post back!
regards
Ben
it sounds to me as if your timing is not advanced far enough. Try bumping the timing a few more degrees and then go for a test drive. One other thing, why do you have such a big carb on yr truck? If it is a 360/390 a 750 is too much carb for the street. It could be that you have no power because of a weak carb venturi signal. Id say if you had a holley 500 CFM of the stock 2 barrel, put that on the engine as well. Id bet that yr problem would be solved. Try the timing first and then post back!
regards
Ben
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At my wits end!@!
750 too much? It seemed to work correctly before this current slew of problems I've been having. I don't have another carb to try, though. I'll try advancing the timing a few degrees and post again in about 30 min.
Greg
Greg
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At my wits end!@!
I advanced the timing about 4 more degrees and fiddled with the idle mixture adjustment screws on the carb, and that seemed to help some, but when I really romp on it, it still doesn't sound like it should.
I also checked the vacuum - it reads 15 in hg at idle with very little fluctuation, and throttle reponse is to go a little lower, then sweep up a bit to about 22 in hg.
Dwell is now at 29.
I don't like to have the timing advanced beyond spec like that. Is there a reason I should have to do that?
I'll check the mechanical advance in a little while and post back.
Greg
I also checked the vacuum - it reads 15 in hg at idle with very little fluctuation, and throttle reponse is to go a little lower, then sweep up a bit to about 22 in hg.
Dwell is now at 29.
I don't like to have the timing advanced beyond spec like that. Is there a reason I should have to do that?
I'll check the mechanical advance in a little while and post back.
Greg
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At my wits end!@!
no mechanical advance on the distributor, only vacuum is working. Is there a way to fix it like stuck springs or something, or should I just return it?
Greg
67 F100 CCS 390 FMX
Greg
67 F100 CCS 390 FMX
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Fleet Mechanic
Joined: Jul 2002
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From: S/W Virginia
At my wits end!@!
well i dont know that much about mechanincal advance, but if its new, i wouldn't try to fix it, just take it back and swap it and see if it acts the same way
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From: Atlanta GA
At my wits end!@!
Hey, maybe I have the same problem!
How much mechanical advance should you get from the dist. w/o the vacuum advance? On mine I only get a few degrees at 1400 rpms. It goes nowhere near 30 degrees.
How much mechanical advance should you get from the dist. w/o the vacuum advance? On mine I only get a few degrees at 1400 rpms. It goes nowhere near 30 degrees.
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At my wits end!@!
I second that last question: How many degrees should one get from mechanical advance for a given rpm range? I only get a couple degrees as well up to 2000rpms. That's still more than I got with the first dist. - nothing no matter how much I revved. The trucks running a lot better now. Thanks for all the rapid response posting guys. 
Greg
67 F100 CCS 390 FMX
Greg
67 F100 CCS 390 FMX
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From: Central Kali
At my wits end!@!
A 72 spec for a 390 for centrifugal advance: Distributor= D2TF-AA. Rpm is dist. rpm
500 rpm = 1.5 to 4.5
750 7.5 to 10
1000 9 to 11.25
1500 11.25 to 13.5
2000 13.5 to 16
Vacuum advance is 9.25 max at 20" Hg.
I do not trust the advance curve in a "rebuilt" distributor.
500 rpm = 1.5 to 4.5
750 7.5 to 10
1000 9 to 11.25
1500 11.25 to 13.5
2000 13.5 to 16
Vacuum advance is 9.25 max at 20" Hg.
I do not trust the advance curve in a "rebuilt" distributor.
Post Fiend
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From: Brea CA
At my wits end!@!
Originally posted by Mike W
A 72 spec for a 390 for centrifugal advance: Distributor= D2TF-AA. Rpm is dist. rpm
500 rpm = 1.5 to 4.5
750 7.5 to 10
1000 9 to 11.25
1500 11.25 to 13.5
2000 13.5 to 16
Vacuum advance is 9.25 max at 20" Hg.
I do not trust the advance curve in a "rebuilt" distributor.
A 72 spec for a 390 for centrifugal advance: Distributor= D2TF-AA. Rpm is dist. rpm
500 rpm = 1.5 to 4.5
750 7.5 to 10
1000 9 to 11.25
1500 11.25 to 13.5
2000 13.5 to 16
Vacuum advance is 9.25 max at 20" Hg.
I do not trust the advance curve in a "rebuilt" distributor.
Double everything when it's on the engine.
Barry
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Joined: Apr 2002
Posts: 7,157
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From: Central Kali
At my wits end!@!
Hi Barry, are you trying to mess with my mind? If you advance the timing by 10 degrees with the vacuum advance, what would be the difference by advancing 10 degrees with the centrifugal advance? The spark still occurs 10 degrees sooner.
Greg, you can take off the distributor plate to get to the springs. They may be too tight or too heavy a spring. Check for any binding of the weights. Is kind of hard to test without a distrubutor machine. I have an old Sun with a spec chart up to 1957.
If you advance the timing by 10 degrees with the vacuum advance, what would be the difference by advancing 10 degrees with the centrifugal advance? The spark still occurs 10 degrees sooner.Greg, you can take off the distributor plate to get to the springs. They may be too tight or too heavy a spring. Check for any binding of the weights. Is kind of hard to test without a distrubutor machine. I have an old Sun with a spec chart up to 1957.