Timing 390 and "dwell"

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70_F100
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Re: Timing 390 and "dwell"

Post by 70_F100 »

R.Smith wrote:I had to reduce the point gap to .010 to get a dwell of 29 degrees and switch the vac line from the throttle body to the metering block to fix the vac advance but, now she's running a lot better, especially from a dead stop.
Are you sure you've got your dwell meter set to "8 Cylinder" and not on "6 Cylinder"? :?

No way are you going to get 29 degrees of dwell at .010" point gap. :nono:

That could also be contributing to your "pinging" problem... :hmm:
Wise men talk because they have something to say; fools talk because they have to say something.--Plato
Why is it that there's seldom time to fix it right the first time, but there's always time to fix it right the second time???

That's not an oil leak :nono: That's SWEAT from all that HORSEPOWER!! :thup:
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Re: Timing 390 and "dwell"

Post by R.Smith »

yep, it was set on 8cyl. I started off at .017 point gap like the book said and the dwell read 21 degrees. I went to a loose .017 and the dwell went to 19-20 so, I went the opposite direction, eventually winding up with 26 degrees on the meter at a .010 gap.
I decided that was as far as I wanted to go so, I reset the timing at 14 dgrees BTDC and after doing this I noticed the dwell had moved up to 29 degrees. Why? I don't know.

I checked and rechecked everything...settings on the meter and which scale was which and connections ect. When I reattached the vac line, the timing stayed the same until I revved it a bit, then the timing advanced. I can't say how much exactly...about 10 degrees maybe...but nothing compared to the radical change that occured when it was attached to the carb base.

I'll try backing the timing off to 12 BTDC and see what happens with the pinging. It's definately a ping and not a tick.
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Re: Timing 390 and "dwell"

Post by 70_F100 »

IIRC, you said that the meter was an old Heathkit meter.

Based on the results you're getting with it, I would try to borrow another meter from someone, and double-check that dwell setting.
Wise men talk because they have something to say; fools talk because they have to say something.--Plato
Why is it that there's seldom time to fix it right the first time, but there's always time to fix it right the second time???

That's not an oil leak :nono: That's SWEAT from all that HORSEPOWER!! :thup:
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Re: Timing 390 and "dwell"

Post by knightfire83 »

When you have the engine running and advance the timing, the idle will probably increase. You have to adjust the carb idle back down to spec. around 6-700rpm. The dwell angle specified is at a certain engine rpm. This could be why the dwell reading changed, but I'm not for sure.

Dwell is usually specified in a range, for an 360/390 it is 26-31 with a point gap of .017.
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Re: Timing 390 and "dwell"

Post by 70_F100 »

Dwell should remain constant throughout the entire RPM range. It can be checked by just turning the engine over with the starter, and that reading should not change with the engine running, whether it is idling or turning 6,000 RPM.

If dwell changes, that is a result of points floating or wear in the distributor (shaft, breaker plate, etc.).
Wise men talk because they have something to say; fools talk because they have to say something.--Plato
Why is it that there's seldom time to fix it right the first time, but there's always time to fix it right the second time???

That's not an oil leak :nono: That's SWEAT from all that HORSEPOWER!! :thup:
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