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Old 03-11-2005, 10:48 AM
A Knight Who Says 'Ni'
 
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Distributor infinite mechanical advance

Hi all, first time poster here. I've searched through the forums (great stuff), but couldn't find an answer my specific issue. The problem I'm having is that my distributor seems to have an infinite mechanical advance. With the timing light hooked up and the vacuum advance disconnected, as I raise RPMs I can see the timing advance like it should, but the faster I rev it the more advanced it gets and just doesn't seem to stop. My initial is set at 12 BTDC, I have the lightest springs in from a recurve kit, and the slot that is supposed to limit the mechanical advance is on "13". That should give me 38 deg total mechanical advance, no more, at about 2500 rpm. But as I increase the rpms above 3000, the advance just keeps going. I've seen it as high as ~55 deg at about 3500 rpms, estimated because it was off the timing marks. I didn't want to rev faster with my head under the hood, but it looked like it would just keep going. Remember this is with the vacuum advance disconnected, so its all mechanical. It seems like the mechanical limiter is not limiting, but since its metal-on-metal post-in-slot, I can't see how that would happen. The timing is solid and smooth (not jumping around or anything), and I've eye-balled the dist gear and it looks almost new. When I let off the throttle it goes back down to 12 like its supposed to. It just doesn't stop advancing. Any ideas what would cause this? This is on a 289 with a stock distributor, pertronix ignitor, and MSD 6A if that helps.


Thanks,
Jay

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Old 03-11-2005, 11:28 AM
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You took the cap and rotor and pickup off, and looked inside of the distributor at the tabs that limit the advance?

I dont know what causes that, but I have bought a few mallory distributors off e-bay that were that way. I didnt have up to 55 but they were getting 32-36 on top of my base timing. An easy fix is to bend the tab inside the distributor.
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Old 03-11-2005, 11:38 AM
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It could be your light.
Some light's act up when using a MSD,The multispark confuses them I guess.
I was timing a 454 HEI dist. with a MSD and it was doing the same thing.Like the timing had no end to it.I got a different light and checking timing was like it is supposed to be.
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Old 03-11-2005, 11:42 AM
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Brainsboy - I took it all apart and everything looks/acts normal. In fact earlier I switched around the advance limiter from its stock 18 slot to the 13 its at now. I thought about closing up the slot some, but then thought better of it because the slot size isn't the problem. It seems that no matter what it's set for, it just doesn't stop the advance from advancing. It just keeps going, and going...

Bee4me - That sounds very possible since I have only used one light, a cheapo Autozone one. I'll try to borrow another light from someone and see if it makes a difference.

Thanks to both of you for your replys.
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Old 03-11-2005, 11:54 AM
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If it looks good inside try bumble bee's advice with the light. For what its worth Im using a Craftsman timing light that does work with the ford ignition and MSD box.
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Old 03-11-2005, 12:26 PM
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Super cheap light work better with multi discharge ignitions than top name good ones. Seems the good ones are little too sensitive to EMF. My dial back light picks up both dicharges and my autozone special only see's the first one. I use a crank trigger MSD with moroso pickup.
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Old 03-11-2005, 12:28 PM
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Unplug your MSD box and see if that makes a difference in the timing indication. Above 3000rpm or so the MSD kicks off its multiple sparking so theoretically the timing should be accurate after that, if its the multiple sparking that the timing light is picking up on causing the mis-read.
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Old 03-11-2005, 01:01 PM
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Good suggestions here. I'll try disconnecting the MSD if a second timing light reports the same thing. Thanks.

Is there a simple way to just shut off the MSD, or would I have to rewire the pertronix back straight to the coil? The reason I'm asking is because I've got the wiring spliced and soldered together and routed nice and neat right now and I'd like to avoid cutting up everything I've done just for a test, if possible.
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Old 03-11-2005, 02:37 PM
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To bypass it you'll have to do rewiring. This is why I usually use male/female connectors on the ends of my wires for quick and easy disassembly/reassembly. This may or may not be the problem. Was just a suggestion. Try the easier things first .
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Old 03-11-2005, 08:02 PM
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Don't forget that 13 degrees in the distributor is equal to 26 degrees at the crank.
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