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Thanks for the pdf.
With me running mechanical only, it looks like my spark is advanced too far.
Initial on my 455 is around 13 degrees at about 650-750 rpm.
I forgot what it was on the higher side.
But it runs fine though with mechanical only.
I will do some checking and see about re-adjusting it if possible.
This is the 3rd car this engines been in, Im the first to remove the heads thats for sure. It might have a bit of a cam but its hard to tell, it kinda sounds like it might. Stock bottom end though.
You should check the RPM and degree of advance when it maxes out - it should be about 36 degrees at about 3,000 RPM.
And you will probably benefit from a vacuum advance. One of the adjustable units will give you the most flexibility.
OldCutlass Eric loves to give people advice about how to dial in their advance settings.
- Eric
I will look for that.
If it maxes out sooner that means there is to much advance so I should retard the timing to compensate right?
Here is an image I found online, it is just like the one in my 455:
http://i.ebayimg.com/23/!BgjrUP!CGk~$(KGrHqIH-EIEsK7W1tc+BLFvY+k46!~~_35.JPG?set_id=8800005007
The carb is a holly 4160, I plugged my VAC advance into the port on the side of the Holly, I believe this is the ported vacuum, is this the wrong port to be using?
Should I be using the manifold vacuum instead?
Is that why I get to much advance with vacuum and its fine without, because the ported vacuum is adding vacuum when the throttle opens, when I should be using manifold vacuum so that the vacuum goes away when I press the throttle?
Last edited by GHOSTOWLGRID; October 10th, 2016 at 01:19 PM.
Reason: fixed
Is that why I get to much advance with vacuum and its fine without, because the ported vacuum is adding vacuum when the throttle opens, when I should be using manifold vacuum so that the vacuum goes away when I press the throttle?
What do you mean by "too much advance"? Depending upon the specific vacuum canister, it can add as much as 24º advance (as the original on my '78 HEI did). This is where the adjustable canister comes in as you can tailor the amount of vacuum advance. Seems the general consensus is ~10º is optimal.
Ported and manifold vacuum will end up being the same once you open the throttle; it's just at idle when ported has no vacuum.
Last edited by Fun71; October 10th, 2016 at 02:00 PM.
Here is an image I found online, it is just like the one in my 455:
You have an HEI
The carb is a holly 4160, I plugged my VAC advance into the port on the side of the Holly, I believe this is the ported vacuum, is this the wrong port to be using?
Should I be using the manifold vacuum instead?
Is that why I get to much advance with vacuum and its fine without, because the ported vacuum is adding vacuum when the throttle opens, when I should be using manifold vacuum so that the vacuum goes away when I press the throttle?
You can use ported or manifold vacuum, with a relatively stock engine it won't make much difference. The argument has been going on for decades.
What do you mean by "too much advance"? Depending upon the specific vacuum canister, it can add as much as 24º advance (as the original on my '78 HEI did). This is where the adjustable canister comes in as you can tailor the amount of vacuum advance. Seems the general consensus is ~10º is optimal.
Ported and manifold vacuum will end up being the same once you open the throttle; it's just at idle when ported has no vacuum.
Reason I asked is because i thought it was right, then I held RPM up, and when I let off the throttle, I had an intake backfire.
That was with vacuum advance on.
With it removed, I think it happened but it was less prone to happening.
This was in park and when letting off throttle after a rev.
In drive while driving, no problems with mechanical only. Never tried it with vacuum as well.
It was repeatable. Is it possible the carb needs adjusted and my timing is fine?
The holly 4160 @ 750 cfm is currently as-is from the box, I never went adjusting anything on it yet.
What do you mean by "too much advance"? Depending upon the specific vacuum canister, it can add as much as 24º advance (as the original on my '78 HEI did). This is where the adjustable canister comes in as you can tailor the amount of vacuum advance. Seems the general consensus is ~10º is optimal.
Most adjustable vacuum advance cans only adjust for how much vacuum it takes to activate them not the amount of advance. To adjust for the amount you need to buy/fabricate a stop that limits the movement of the rod. What your looking for is around 50-54*BTDC of total advance with vacuum at cruise rpm, any more will cause detonation and surging.
This is the Crane Kit 99601-1 it comes with advance springs to set your curve, an adjustable vacuum can with allen wrench, and a stop thats stepped at different degrees of advance settings.
Ported and manifold vacuum will end up being the same once you open the throttle; it's just at idle when ported has no vacuum.
Do you have an adjustable timing light? What is your timing set to?
Backfiring through the carb sounds like a carb related issue and not so much a timing issue.
What would cause a brand new holly 4160 @ 750 cfm to do that?
To lean?
I never adjusted the carb yet.
Maybe my spark is/was fine and the carb is what I should be adjusting?
I dont recall anything like this with the factory carb.
Last edited by GHOSTOWLGRID; October 10th, 2016 at 03:10 PM.
Reason: added
I remember a friend's engine would backfire and shoot flames out the carb when letting off after revving. There was a plug missing either in the rear of the carb base plate or the intake manifold, either way it had a big vacuum leak.
If you are running 12* at 750 rpm its most likely too low. I'd set it to 16-18* and tightened the distributor down. With the engine running and timing light hooked up, connect our vacuum advance line to manifold vacuum and note how much more timing you get.
0-76750BK is a double pumper(mechanical secondaries) and 4 corner a/f adjustments. Not a simple carb and a bit extreme for a mild 455 with an automatic.
October 9th, 2016, 11:35 PM
