Reviving a '68 GTO with a twist! - Pontiac GTO Forum
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post #1 of 8 (permalink) Old 08-11-2014, 12:04 PM Thread Starter
 
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Reviving a '68 GTO with a twist!

Hi guys. I'm a "new" member on here and wanted to get some opinions of you all while I begin my journey in restoring my dad's 68 goat that's been a garage queen for over 20 years! This is intended to be a father /son project. In no way are we novice , I currently own two cars and have built my turbo charged one from the ground up so to speak. Only problem is most of my experience is on imports. Never old American muscle. So with that said, we've been having an issue with starting the car. It turns over fine and wants to fire up but once it does, it gives a loud bang out of the carb and shuts off. I recently bought a new holley 600 carb for it and the same issue occurs. Granted I haven't hooked up the electonic choke since I'm not sure where the ideal place would be for this. We have changed the ignition components as well. I was also wanting to order a new engine harness as we had a rat infestation and are sure there are chewed up wires somewhere along the harness. Here's the twist: this goat has a 428 with a .30 overbore engine and Trans from a 69 bonneville. So would the harness have to be for the bonneville or gto? Thanks for all input guys! I'll be posting pics up soon
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post #2 of 8 (permalink) Old 08-12-2014, 12:14 AM
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Given what you've said and the symptoms you describe, I'd say it's most likely ignition timing. Try advancing it in small increments and see if that makes a difference. (Remember Pontiac distributors turn counter-clockwise).

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post #3 of 8 (permalink) Old 08-12-2014, 12:18 PM
 
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Just grasping at straws here but could the popping back through the carb be caused by TOO much advance? Let’s say the static timing is too high. The engine would start and then the vacuum advance adds about 16 degrees more and POP!! back through the carb.

What about valve timing? Worn timing chain?
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post #4 of 8 (permalink) Old 08-12-2014, 02:53 PM
 
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I would think you are ordering a harness for a 68 with AT with or without AC. To be sure, I would contact M&H Electrical for your harness. Excellent tech support. Matt

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post #5 of 8 (permalink) Old 08-14-2014, 10:10 AM Thread Starter
 
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hey guys, so we were able to start up the car! turns out the new carb wasn't getting enough fuel, so we swapped the fuel pump and she fired up! now the problem is an occasional misfire happens. We tried checking the timing but its reading WAY off. it is no where near the timing tab with the notches. I know for the imports I have worked on, you need to get them into a "diagnostic" mode by jumping the ignition before you can read timing. Is there a procedure in reading timing on these cars? I do have the strobe and I did locate the correct notch in the harmonic balancer. Im just surprised the reading is way off. it overly retarded according to the reading. We tried to advance it back to the first tab on the block, and the idle smoothed out alot, but the car would not turn off. We had to retard it back to where it was in order for the car to turn off... is there some other factor coming into play here? Also would anyone happen to know where to find the casting number on the 428 block? I am going to call up Painless harnesses with the casting number on hand to see what their recommendation is with the harness. I will be starting a tear down this coming week. Fenders, hood, interior is all coming apart. Has anyone had experience with installing a new harness? any tips/tricks? Cant be anywhere near as hard as 90s turbocharged jap cars no? haha Thanks guys!
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post #6 of 8 (permalink) Old 08-14-2014, 10:18 AM
 
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Engine harness on a 68 is a piece of cake. Well... the starter wires are never fun, but other than that, all good. Matt

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post #7 of 8 (permalink) Old 08-15-2014, 12:37 PM
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You need to go to basics here. Disconnect the vacuum advance line and plug it. Set the base timing at idle to 6 -9 degrees. When you hook the vacuum advance back up, it should be to manifold vacuum. This will immediately advance the timing at idle, which is what it's supposed to do. If you rev it to 3000 rpm and use your dial back timing light, you should have about 40 degrees total timing. After the timing is set, you can adjust your idle speed and carb mixture. Good luck.
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post #8 of 8 (permalink) Old 08-21-2014, 11:19 AM
 
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I would say that you should separate the issue of the engine running smoothly, i.e. timing, and the being able to turn off the car. In other words, the fact that the car won't turn off should not be caused by the timing of the engine.
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