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Discussion Starter #1
The car is popping going down the track so we changed the jetting down from 210's to 196's and the pop stayed the same, making us think that we have an ignition problem. Any idea's? What voltage do we actually need for the MSD 7AL-3 to really work well? It is a brand new box. Thanks for the help!
 

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Bracket racer
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You don't have two plugwires crossed do you? Also, does the car have an alternator?
 

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Exhaust rocker backed off will raise hell too. MSD connector wires reversed (the purple/green to and from the magnetic pickup) will act stupid at high rpm and have sharp backfire type sounds thru the exhaust. 7AL-3 boxes don't have a good track record, there is too much stuff inside and they don't deal with the heat very good, they are a 7AL-2 box with those additional features on seperate cards plugged into the main buss so there is lots of places to have a problem, i have MSD testing stuff and in 10 years of testing i have found a couple bad 6's and the odd 7 (most problems are peoples' wireing) but to date i have tested about 4 of the -3 that have had to go back.
 

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Just for shits and giggles,sorry, but how old is the cap and rotor ? Is it fine at idle and up to a caertain rpm ? or does it do this at a load ?
 

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Discussion Starter #6
It is backfiring out the exhaust and usually only past the 330' of the eighth mile. I don't have an alternator, I have two optima red top batteries. The cap and rotor is older.

We just checked the rocker arms on thursday night at the track when we were looking for reasons for the popping. The car runs great around the pits and while sitting at the trailer, even if you rev it up.
 

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barndoorslammer
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If you charge batteries between passes, 2 red tops should be fine. I have run a 7AL3 for several years now, and so far it's been good.
My engine would have the occasional popping sound through the exhaust if it was lean. Also, what is the ignition timing set at?
 

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barndoorslammer
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It could be too much advance. When I used "industrial" methanol, I had to run about 38* advance, finally I bought some Torco (or it might have been Monster, anyway) .... I was able to retard the timing and it ran its quickest pass ever.
Next time you're out racing, make a couple passes at 36*, then retard the timing to 32* and see if the problem goes away, you might even drop some e.t.
 

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It is backfiring out the exhaust and usually only past the 330' of the eighth mile. I don't have an alternator, I have two optima red top batteries. The cap and rotor is older.

We just checked the rocker arms on thursday night at the track when we were looking for reasons for the popping. The car runs great around the pits and while sitting at the trailer, even if you rev it up.
If you checked the rockers I'm sure you looked for broken springs too. My engine starting popping through the carb and I found a broken intake spring.
 

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i had the same problem after putting engine back in car we had distributor plug in backwards still started and run just popped adn cracked and timing jumped every where turned it around and evrything was fins just a thought
 

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My buddy just went through a similar problem.Had car mini-tubbed so it sat a while, put brand new valve springs on before 1st run.1st run noticed a miss and would not rev past 6300, 555 ci bb chevy.Replaced entire ignition system, rebuilt fuel pump, re-wired entire ign. system. No better, He just found 2 broken springs.

Good luck
Mike T
 

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My buddys BBC in his 63 impala was doing the same thing and we chased everything we could think of down , so this last winter we decided to freshen up the motor and found 2 inner broken valve springs . I bet it wont be popping this year !
 

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I had one that did that and it was the coil wire not staying seated on the terminal, the car I have now was doing that and the battery was bad. I changed carbs, distributors, springs, fuel and it was a battery. Showed good voltage, but was something internal I guess.
 
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