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I have a Pontiac 400 in a 1976 Nova(Ya I know), we have installed everything and I just can't seem to get the timing dialed in right without it popping through the exhaust or back fire through the carb. I am at my whits end on this. We lined up the dots at 12 and have the rotor pointing at #1. Any help Please. Its a 1976 400 with Edlebrock heads a hyd roller cam Performer intake with headers. heads are the 87CC.
 

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I take it you know the firing order on a pontiac goes counter clockwise?
Yes, I had a 400 in my firebird and then a built 455, but it’s been 20+ years since I have tried to tune in a car and I’m getting frustrated that Zi can’t get this thing timed right
 

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Discussion Starter #5
I don't think so but I am not the one that set them, that is something I haven't thought about
 

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I'm not sure what the history of the engine is, but, I purchased a lemans once, it ran reasonably well, and I did a tune up to it and couldn't get it to stop back firing everywhere. It took forever to figure out that the last person that had it, must have put the distributor in 180 degrees off, and so their fix was to grind off the tabs on the rotor so that it would fit right. I didn't notice that when I took it off. When I put the new rotor on it fit just fine but unknowingly to me, it was now 180 degrees off. So the moral of my story is to make sure the rotor is also pointing to the #1 cylinder at the right time.
 

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Could be too much timing advance. You may be getting it from the weights, a spring could be off, or they are stretched to nothing or stuck open. Remove the dist cap and look under the rotor.

Are you disconnecting your dist vacumn can to set base timing? If not it can add timing when you are cranking that may be too much.

Petronix ignitions and others drop the timing four degrees during cranking To avoid hard cranking and backfire, because of too much advance.

if you are running points the dwell must be set right and condenser working. Check point gap with a feeler gauge. Point cam on high part of lobe....

make sure all ground wires inside dist are attached and tight. Cap and rotor must be on right, clean and no corrosion.

also try to retard your base timing and crank it. Drop it down to 4 degrees BTDC and try it.

you turn the dist against rotation to advance,...clockwise to advance .....

turn with rotation ..counterclockwise ..to retard the spark.

like bulk judge said could be valves, even a broken valve spring. Remove the valve cover and look at all the springs, any cracked? Or broken? That will do it.

so there are some easy things to look at...you will get it stay with it!
 

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Good on ya for putting a real engine in that chevy! Love it... (y)

Take a step back --- if you've checked and double checked the cam timing and it's still doing it, then maybe the problem isn't cam timing. I had a problem with mine like that, and it turned out to be a problem with the mechanical advance mechanism in the distributor. It was completely non-functional, as in no advance at all so whatever it had from the initial setting, was all it got. As soon as I hung my foot in it, it bucked, spit, popped, banged, and all sorts of related ugliness. The pins that the advance weights pivot on had worn, allowing the weights to get really floppy/sloppy, and with my legendary luck I'd managed to install the rotor with the ends of the weights overlapping each other such than when I tightened the screws, it quite effectively locked them down so they couldn't move at all.

Also check your fuel pressure to make sure it's not high enough to force the needle off its seat and start flooding/overflowing the fuel bowl.

Look for gasket leaks, vacuum hose leaks, etc that might be making it go way lean.

Bear
 
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