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Old 01-20-2011, 04:49 PM
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poncho 400 timing issue

So i drove my poncho from san diego to bremerton, wa without a hitch.
The carb gave me a little grief at first but thats basically taken care of. When i had the carb tuned i asked the guy to please check my timing. I told him i wanted 14 initial and a total of 34-36...so 20 or so off the vacuum. Standard stuff.
He comes back and tells me my initial is indeed 14 but my total tops out at 43!!! I balked at this but he somehow reasoned me into it and the car runs great with no -audible- pinging. I even pulled spark plugs when i got here (they were brand new when i left) and they look...perfect.
I tried backing the distributor off to where i wanted it and the car really just doesnt run too well like that.
There is definitely the presence of an aftermarket cam but i dont know the specs. No lope, i assume its an RV type deal.
I read a faulty ignition switch can cause a car to like more timing due to lack of voltage. Im ashamed to admit that at the moment the switch is a little rigged. I actually fixed a lot of the ignition probs when i got it...but i would still consider it rigged.
Plan is to turn sd performance loose on it at the end of the year but id like it to last through the summer. What do you guys think?
400 is a '73 run on premium.

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Old 01-20-2011, 05:07 PM
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Your engine wants all that initial- but does NOT need all that much total. 36 or so is usually plenty for an iron head Pontiac.

If the timing was read to be 43 with the vacuum advance disconnected and plugged, the total timing needs to be limited.

This can be done by welding or brazing up the slot that controls the total mechanical timing or by changing to a different weight and cam set. Problem w/changing the weights, is they're hard to find and the replacements that come in the advance kits suck. That leaves you w/welding or drilling the advance plate for a screw to limit the travel of the advance plate.



The vacuum advance may be adding too much advance- usually 10 to 15 max is plenty. If you want to limit it, use a vacuum advance limiter plate like the Crane #99619-1, #99619 Instructions.
Or you can easily make one.

You can MAKE A TIMING TAPE to see what the total timing is, w/o needing to use a dial back timing light. You can also buy a timing tape, they're not very expensive. The problem is if you have a different diameter damper than what the timing tape is made for.
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Old 01-20-2011, 05:14 PM
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I stood and watched, it was 14 with the vacuum disconnected. Reconnected and revved to about 2800 rpms it totalled out at 43.
Thanks for your help, ill look that stuff up.
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Old 01-20-2011, 05:23 PM
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If the mechanical was truly all in at 2800 RPM, it sounds like the springs are nigh-on perfect. Just be sure the timing hasn't climbed any more at, say, 4K RPM.

The 'tell' for too much vacuum advance (in case you were wondering) is a surge at light throttle cruise, and/or a ping on throttle tip in. With premium fuel, the ping @ tip in might not ever show up.
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Old 01-20-2011, 05:27 PM
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Oooh i was wondering about that, if maybe the premium would cover some of it up. It does have this quirky thing it does cruising in 2nd going to third, when it gets to 2000rpms it will drop real quick to 1800 then climb right back up. Its always done it and no one seems to have an answer why. Doesnt surge though.
Thank you cobalt!
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Old 01-20-2011, 05:56 PM
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Quote:
Originally Posted by 67TEMPtress
It does have this quirky thing it does cruising in 2nd going to third, when it gets to 2000rpms it will drop real quick to 1800 then climb right back up. Its always done it and no one seems to have an answer why.
TH400? Possibilty it's in the timing of the band release, or something internal to the trans.
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Old 01-20-2011, 06:13 PM
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700r4..... i figured it was trans or tc related. Its the only idiosyncrasy it really has.
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