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Unread 05-05-2013, 08:29 PM   #1
2Xtreme
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Help me solve this blasted Pinging....

79 CJ7, 258 - stock internals
Holley 390, Offenhauser intake, Hooker header...

Jeep has a terrible ping on acceleration/ under load. Had the timing set which improved it a good deal. But mechanic said it was 'about as good as he can get it, probably due to the carb'.

I'm thinking I need ignition improvements to take advantage of the carb.
I've had this thing for 3 years and not been able to drive it much, so I don't even remember if I ever did anything with the wires/ cap/ etc that were on it when I got it.

So my questions are these:
Am I on the right track in thinking I need more spark due to the bigger carb?
Should I start with replacing the stock ignition parts to see if that gets me anywhere?
Or jump into and HEI/ DUI set up?

Thoughts/ Opinions?

Thanks in advance!

2X

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Unread 05-05-2013, 10:59 PM   #2
82JeepCJ7
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The advance timing is off in the distributor. Also, where is your vacuum advance hooked up? Ported vacuum or manifold vacuum?
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Unread 05-05-2013, 11:51 PM   #3
hutch1200
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http://www.ebay.com/itm/NEW-AMC-Jeep...41c4be&vxp=mtr
You may want to try this. Gotta start somewhere, no? I would caution you to use you OLD distributor gear on the new CRT unit, as the gears MUST be a matched set. W/this deal, you get the correct plug wires (which you likely need anyway) and open your NEW plugs up to about .40-.45
And like 82JeepCJ7 stated check where the Valium advance is hooked up. All the Kool kids are using Mani-vacuum. While you're at it, try to find an old, small shop that has a dizzy machine that can give you the best advance curve for your setup.
Good luck and let us know how ya make out.
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Unread 05-06-2013, 01:11 AM   #4
TIPPEDITOVER
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Assuming your mechanic checked out all aspects of the ignition system and all was correct then he is right. It's a lean air/fuel ratio. Installing the correct metering jets might cure it. Maybe. Enrichen the air/fuel mixture and cool the combustion temps. That will stop the pre-ignition.

The engine is only going to pump the volume of air it pumps. Yours has stock internals. Putting a bigger carb on it does absolutely no good, unless you've significantly increased the volume of air the engine can pump through itself. I'm not understanding why this was done for a stock engine.
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Unread 05-06-2013, 01:43 AM   #5
Caish
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I would like to know what jets are in the carb too,
But till then, try removing the vacuum like from the distributor so your just working off the mechanical advance.
I would hook up a timing light and see what is going on there too, you should be able to see it advancing as you
rev the engine.
Use some orange nail polish and use the timing marks on the cover and turn the damper till the stock mark hits 10*
now make a mark at 0* and move that line to 10* and repeat till you have 5 or 6 lines.
Now you have 50 to 60 degrees of timing marked off and you can see what the advance is doing.
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Unread 05-06-2013, 01:45 AM   #6
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I've read up on the Holley 390. Surprisingly it is popular in some parts of the Jeep world and it's said that it is not too much carb for a stock 258. Ok that said, then check that the float level is adjusted to the correct height and it's jetted correctly. Let us know how it turns out.
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Unread 05-06-2013, 07:19 AM   #7
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Wow.. this sounds like a lot of stuff that's over my head.

A few points to ponder.

I went with the 390 based on a friends recommendation. Guy is a great mechanic who was going to help me with this thing, but tings change. So I am stuck with half of what he had planned for recommendations.
I know the jets that are in it, are whatever came with it. (F)51 (R) plate 134-34 (whatever that means), if the information I found online is correct.

To be honest, I am not sure what the mechanic looked at. I asked him to set the timing. I assumed a good mechanic would have gone over all aspects.

I am working two long days before going on vacation until Sunday, so I won't be able to attempt anything until then. Gathering info and researching right now. I can post up some pics of vacuum routings tonight, if that will help.

Again, thank you for the input!
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Unread 05-06-2013, 11:17 AM   #8
John Strenk
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It could also be carbon build up on the pistons, too hot of plug (heat range)

I don't think the type of ignition will have a huge effect unless the timing is wayyy off or the harmonic balancer is...

Could be a broken spring on the mechanical advance...

Don't forget the vacuum advance should not be in effect under load.
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Unread 05-06-2013, 02:05 PM   #9
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Cfm

"Enrichen the air/fuel mixture and cool the combustion temps. That will stop the pre-ignition.

The engine is only going to pump the volume of air it pumps. Yours has stock internals. Putting a bigger carb on it does absolutely no good, unless you've significantly increased the volume of air the engine can pump through itself. I'm not understanding why this was done for a stock engine."-
TIPPEDITOVER
.
I agree w/running it rich to cool it internally. I do this on every Harley rebuild during break-in.
I'm not familiar w/holleys. Is this a 4 Bbl? Thanks for any info you can share.
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Unread 05-06-2013, 03:26 PM   #10
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Yes, 4 barrel
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Unread 05-06-2013, 07:16 PM   #11
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OK, I ran to the garage after work to snap some pics of the carb and vacuum setup. I don't know if they will help, but here they are....

Driver's side:




Front:




Passenger's side:




Vacuum routing:



So. There they are.
Lemme know your thoughts!

And... as always.... THANKS in advance!
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Unread 05-06-2013, 09:25 PM   #12
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"Lemme know your thoughts!"-2Xtreme
Whoa...what a huge temptation there!
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Unread 05-06-2013, 09:55 PM   #13
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Quote:
Originally Posted by hutch1200 View Post
"Lemme know your thoughts!"-2Xtreme
Whoa...what a huge temptation there!
HEY!!
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Unread 05-06-2013, 10:09 PM   #14
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I'm being respectful here. I didn't mention anything about the gov't putting microphones in our shorts or nothing about con-trails.
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Unread 05-07-2013, 12:15 AM   #15
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Yep, it's a 4 bbl, and that's a good setup. It's a vacuum secondary carb, so the majority of the time, you're running on 195 cfm. And not even that, since Holleys don't actually flow what they're rated.

Pinging, I'd agree, is caused by too much timing. If your timing was set by the timing marks on the balancer, it's probably slipped and therefore wrong. So the timing would be wrong.

If it hasn't been set, check it.
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