60 degrees of initial advance?? - Pontiac GTO Forum
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post #1 of 37 (permalink) Old 03-31-2017, 02:31 PM Thread Starter
 
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60 degrees of initial advance??

Getting my car running after years of sitting. After dialing in idle (16 inches of vacuum) and float levels, she ran pretty good. She idles fine. Pushes you back in your seat. Only rough spot is that she surges when you're cruising with light throttle. (Thought maybe that was too much vacuum advance or lean.)

Then I checked the timing. With vacuum advance plugged, she showed 60 degrees advanced initial! Huh? Used a different timing light. Same thing. No knocking during idle or driving. I turned the distributor to take out some advance. It immediately ran worse. Couldn't get down to the teens or it would die. Hmm... Got a piston stop out and confirmed the dampner hasn't shifted. TDC on the timing tape is still TDC for #1 piston.

What am I missing?

65 GTO with 400. 6X heads. 770cfm Holley. Pertronix HEI. MSD. Only 1,000 miles on the build, but she has sat for years at a time.
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post #2 of 37 (permalink) Old 03-31-2017, 03:24 PM
 
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Unhook vac line & plug it off.

Find out what your TOTAL MECHANICAL ADVANCE is first. For most Pontiac engines it should be 34-36 degrees.

Check the rpm at which you reach TOTAL advance.

If that number is above 3500, you need to buy an advance curve kit, and substitute a weaker spring, til you get the total to stop advancing at between 3000 & 3500 rpm. Most want their curve to start advancing at about 1000 and increase to total, by 3000.

AFTER you have the MECHANICAL curve set correctly, then you can hook the vac line back up & see how much advance the vac can adds.

I've read that you don't won't it to reach above 50 degrees. Some say mid 40's is enuff. If your dist has an adjustable vac can, you can back it off all the way, and if that's too low, adjust it back up in small increments. If your vac can is not adjustable, you can buy a Pertronix adjustable. Or, you can buy a Crane vac advance kit, which comes with an adjustable vac can & weaker advance weight springs.

https://www.summitracing.com/parts/p...QpOBoCy1Tw_wcB

https://www.summitracing.com/parts/crn-99600-1
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post #3 of 37 (permalink) Old 03-31-2017, 03:55 PM Thread Starter
 
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Thanks bigD. I measured advance with vacuum advance disconnected and plugged. I know the targets to shoot for. Where I'm at a loss is that it shows 60 degrees initial and likes it! Throttle response isn't as great in the lower end of the rev range, but I thought for sure it would be knocking and pinging if I had several times more initial advance than anyone I know. No detonation that I can hear. And she starts right up every time. Something's up and I don't know what.
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post #4 of 37 (permalink) Old 04-01-2017, 08:24 AM
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I agree, something's not right here. If it really has 60 degrees in it I'd expect it wouldn't even start. Please forgive me "in advance" (lol) for asking a really dumb question, I'm not trying to insult your intelligence or anything, but you are connecting the light to the front cylinder on the driver's side, right?

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post #5 of 37 (permalink) Old 04-01-2017, 10:09 AM
 
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"...you are connecting the light to the front cylinder on the driver's side, right?..."


Yeah, you can hook it to either #1 or #6 wire, since the zero mark on the balancer will hit the zero mark on the timing tab when every time either #1 or #6 piston is at TDC of it's compression stroke. It's a bit easier to use #6 , on a Pontiac, since you point the light from the pass side.

The timing light doesn't know which wire it's hooked to. It just flashes when the charge comes thru the wire. So, you can hook it to each wire, to make sure every wire is firing. But, for timing purposes, you must hook it to either #1 or #6 wire.
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post #6 of 37 (permalink) Old 04-01-2017, 12:41 PM Thread Starter
 
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Thanks for the replies guys. No offense taken!

I know my light is on #1 wire. Driver side at the front closest to radiator. Two different guns got same reading. Neither gun of the dial back variety.

Plug order on cap is right. 1,2,3,4... Just kidding. : ) 18436572 counterclockwise.

I pulled distributor last night. Put #1 piston 12 degrees before TDC on the compression stroke (watched intake valve open and close to confirm that), then took off the distributor cap. You would expect rotor to be pointing right at #1 terminal. It was noticeably past #1 terminal. I think this confirms that indeed it has a LOT of initial advance. Rules out the gun and the tape being the problem I think.

I can play with weights and springs, but what has me stumped is why would it want 60 degrees? Doesn't make sense.

If cam and crank gear were out of whack it wouldn't want THAT much advance would it? Timing chain and engine build only has about 1,000 miles on it. (And I've timed it before since the build!) Also, why would it run reasonably well if cam and crank were way off.

When I degreed in the cam, I remember talking with a builder about advancing or retarding the cam itself. I remember he was asking if I had a crank offset key. I can't remember what I did on that if anything. But if the cam was a little advanced or retarded, it wouldn't dramatically change my ignition timing, right? 60 degrees at idle isn't a tweak.

I really appreciate all ideas and help.
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post #7 of 37 (permalink) Old 04-01-2017, 01:56 PM Thread Starter
 
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Just checked my timing tape. Measured the circumference. Then measured the distance of 40 degrees worth of marks. It's the right one. Still scratching my head.
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post #8 of 37 (permalink) Old 04-01-2017, 07:18 PM
 
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Hey, maybe it's just playing a April Fool's joke on you. I'm pretty sure an engine will not idle @ 60 degrees advanced.

Hey, just for kicks, humor me and hook a light up to #6 wire. It should read exactly the same as when on #1 .
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post #9 of 37 (permalink) Old 04-02-2017, 10:21 AM
 
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65Poncho....That surging and bucking at light throttle cruise too much timing advance...

if your centrifigal and base is high, adding in 16 more from vac is way too high....

that said I have had guys say their car runs pretty good, when we pull dizzy and put it on the machine it has so much adavnce cannot believe they drive it like that!

some will have 40 in the weights and adding more on the base......then another 22 from vac....

what usuaslly saves them is heavy springs nd it keeps all that advance from coming in until way up in the rpm range.....

60 at idle....seems like it would be awful hard to start that....

you want 36 total Mechanical and 46 to 48 with vac....

hot cams can take a little more base and a little less cetrifigal....

the vac can add ten more

sometimes the worse knocking is the knocks that you don't or can't hear!
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post #10 of 37 (permalink) Old 04-02-2017, 10:31 AM
 
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PS....double check for a crossed plug wire...as was mentioned ....

be double sure that you are not just clipped on the wire at the No 1 plug but that that plug wire is actually at the corresponding place on the cap''''

sorry, if you already verified, but this can happen easy...
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