pinging without vac. advance working? - Team Camaro Tech
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post #1 of 9 (permalink) Old Jul 29th, 00, 10:17 AM Thread Starter
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Hi Everyone,
I posted a ? a while back about the timing on my '68 with a stock 350, auto, & HEI. Initial timing is 10 degrees set WITHOUT vac. advance hooked up. Car starts easy but pings like hell on WOT, even with vac. advance unhooked. I have been playing around with springs and weights and can't seem to make any progress. I even bought a Crane adj. vac. advance, but when i hook it up, pinging is worse. How can it be detonating on WOT with no vac. adv., yet still start easy? Please help...this car is driving me beserk!!!
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post #2 of 9 (permalink) Old Jul 29th, 00, 12:03 PM
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We just had a big discussion on it in the troubleshooting section.
Take a look there on "big block vac advance problem"

You need to limit your total amount of centrifical advance.
If you set static at 10 degrees, you need about 26 degrees of advance in the distributor so the total advance comes to 36 ot 38 degrees. 10+26=36
IgnitionMan would have better numbers than I list here, this is just an example and fairly close.
Most stock distributors have more advance built into them than that.

Distributor advance is limited by a pin on the bottom of the advance mechanism that fits into a slot on the breaker cam piece.
There is usually a plastic bushing or rubber bushing (older point dist) over the pin from the factory.
Often they come off with age and high rpm's and allow the distributor to advance even more than intended.
The breaker cam slot ( on a HEI it's called something else but functions the same) has different length slots depending on the engine and application, which limits total advance degrees.

Most aftermarket kits have a bushing that goes over the pin but you may have a long slot in your cam that gives too much total advance.

Get it reworked by someone like IgnitionMan, he's got it all handled. He can even make a small body HEI out of a stock distributor.

You need to learn how to set for total advance timing with a timing tape if you don't allready.
David


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[This message has been edited by davidpozzi (edited 07-29-2000).]
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post #3 of 9 (permalink) Old Jul 29th, 00, 12:50 PM Thread Starter
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Thanks for the info David. I'm going to the troubleshooting section now to check out the post. I have always heard about the "stop" or limiter but no one ever told me where it was. If I plug the vacumm adv. line, and turn the screw on the adjustable advance all the way counterclockwise, it starts fine and runs WOT with no pinging. But if I turn it clockwise 3-4 turns, I get pinging. How can this be with the vac. advance line not even hooked up? Thanks for your time.
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post #4 of 9 (permalink) Old Jul 30th, 00, 09:26 AM
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I have not used that crane advance. But it sounds like when you are turning the screw the base timing might be changing.
The advance attaches to the point plate so if turning the screw moves the plate, that would change your timing setting and advance the whole curve.

I'd re check timing at idle every time you change the vaccum can screw.

Also make shure your dwell is set exactly right if you are using point ignition. 1 degree of dwell is equal to two degrees of timing change at the crank!

If you change points in the future and get the dwell even 1 degree from perfect, the timing will change 2 degrees.

I also like to come up to the final dwell setting by turning the adjuster screw by turning it clockwise. That way I feel the setting will stay put. If you come up on the final dwell setting by unscrewing the screw it might allow the points to have more slack in the threads and open up the dwell with age.
Here's the link to the discussion we had in troubleshooting. There are probably plenty of others, it's a common topic. https://www.camaros.net/forum/Forum5/HTML/000440.html

IgnitionMan has as good a setup as I've seen for converting to electronic ign and correct curve. I was dissapointed to find out MSD used a vaccum advance that had so much advance to it.
David

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[This message has been edited by davidpozzi (edited 07-30-2000).]
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post #5 of 9 (permalink) Old Jul 30th, 00, 03:08 PM
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Sounds like the mechanical advance gets to its full rpm stop too soon, needs heavier spring(s). Read on, please. Large cap HEIs are no fun to get right, best to just get to it and done.

One point about the adjustable cannisters from Crane, as you turn the adjuster screw near the limit of its travel invard, tightening the spring, you also move the point plate/pickup housing as well, which advances the timing by moving the plate/housing.

Also, sounds like you are using a ported source for the vacuum advance, and this is a full bore NO-NO. You want the vacuumm advance to add about 10 crankshaft degrees to the IDLE, to help idle quality, not add more timing to the upper end of the rpm span as ported vacuum source does.

If it were mnine, I'd set it up this way:

Initial timing at 12 BTDC, lowest idle speed I could get, vacuum advance disconnected.

Set mechanical curve to start at 900/1,000 rpms, and stop at about 2,600/2,800 rpms, and give 24 curve degrees, for a total of 36 crank degrees.

Vacuum advance should be set to give 10 crankshaft degrees, and connect it to full manifold vacuum after initial timing is set.

Go to carb steeings only after you get the timing resolved.

This should get you cvlose, so you can do some further tuning work on it.

[This message has been edited by IgnitionMan (edited 07-30-2000).]
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post #6 of 9 (permalink) Old Jul 30th, 00, 04:31 PM Thread Starter
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I have my vacuum advance hose connected to the port on the driver's side of my edelbrock 600 carb. I'm pretty sure this is full manifold vacuum. Can someone tell me? There are only 2 ports on the front of this carb, side by side with the PCV inlet between them. Ignitionman, I'm pretty sure you will be getting 1 of these old point dist. I have laying around to convert over for me. Where can I find some info on them?
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post #7 of 9 (permalink) Old Jul 30th, 00, 05:47 PM
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I'm running the Edelbrock 600 also.Yes,the drivers side is full time vacuum.

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post #8 of 9 (permalink) Old Aug 2nd, 00, 03:56 PM
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When I went to school at wide open throttle vacumm is all most non existant, so with or with out the vacumm hooked up makes no difference, the problem lies on the mechanical side, also how is the engine condition, is it a high mileage engine a build up of carbon on the piston will cause you more grieve.
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post #9 of 9 (permalink) Old Aug 4th, 00, 02:45 PM Thread Starter
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So, let me get this straight. If I am having pinging at WOT with the vac. adv. disconnected, then I need to adjust on the weights and springs? They control rpm and the vac. adv. controls load conditions right? The motor doesn't have 10,000 miles on it, but has been detonating for a year now. I hope and pray it hasn't damaged anything already. If I plug the vac. adv. and stomp it from a dead stop, it boils the tires but runs out of steam about 4500 RPM. Some posts I have read say only change the center cam, not the weights. If I plug the vac. back up, it pings like hell. I'm thinking the advance plate in the HEI may be sticking because sometime in the morning it is hard to start like timing is advanced too much. May drive it 20 miles, kill it...and then it spins over forever spitting back through the carb like it is retarded. This has stumped everyone I have taken it to. I am about ready to order a new dist., but this is the third HEI I have put in with no difference. Thanks for the replies.
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