Question for those of you with Old-school experience

[infernus]

Ok, so I rebuilt the 400 in my Grand Prix last year (upgrades include: .060" overbore, heads hardened, .480"/230° cam, 1.6:1 roller rockers), and in between fixing coolant leaks and cussing the exhaust work (and headers seem to be out of the question because its stick... I've tried 3 different sets that claim to be for that model and none fit... Summit sucks), I've not been able to tune out the backfiring. Now, the gas in the tank is about three years old, and I know that doesn't help, but I'm not sure how to get it out and put fresh stuff in. Can I just shove a tube down the filler neck and pump it out by hand, or do I have to disconnect a hose and drain it from the bottom?

I still have the stock distributor with points (shut up, I'm keeping them...) and vacuum advance. So far using a timing light setting the spark plugs to 6° before TDC then trying 9° per the spec in the factory manual seems to make it worse, and it wants to quit when I put a load on it. But, if I simply adjust the timing by ear it runs much better. Does having a much hotter cam than stock affect where you set your timing?

Sorry for all the questions, but this project has really turned into a can of worms, and I'd like to just get the old gal back on the road again.

[Jchiasson]

Can I just shove a tube down the filler neck and pump it out by hand, or do I have to disconnect a hose and drain it from the bottom?

But, if I simply adjust the timing by ear it runs much better. Does having a much hotter cam than stock affect where you set your timing?As for the gas tank, stick the tube in and get out as much as you can.

When you start getting in to performance cams, yes you have to adjust the timing accordingly (might have to adjust the advance also). In a stock setup the spark will happen just (and i mean milli seconds) before both valves are closed.
With a performance cam your changing when and how long the valves open/ close, so you have to adjust timing accordingly.

At least that's my general take on it. Never got to big in to engine mods.

[gt00]

I still have the stock distributor with points (shut up, I'm keeping them...) and vacuum advance. So far using a timing light setting the spark plugs to 6° before TDC then trying 9° per the spec in the factory manual seems to make it worse, and it wants to quit when I put a load on it. But, if I simply adjust the timing by ear it runs much better. Does having a much hotter cam than stock affect where you set your timing?

First off get rid of the points and get an HEI or other aftermarket unit ( much better ) , you need to recurve the distributor timing with that cam . Try an adjustable vacuum advance can and limit the vacuum advance ( or disconnect it ) and see what happens . The fact you are getting back firing is a clue the distributor is not up set correctly .

;)

[Greengo 07]

go to hotrodders.com its an excellent site and they really know theyre stuff there, they will most definitely be able to help you with all your questions

[RickHigginsHtbr]

yes, fix your timing, doing it by ear is going to make it better, but don't go by factory specs even if you put a semi mild cam in it. What are the headers hitting that they don't work. Make them fit! haha, just make sure you gettin pontiac 400 headers and not SBC headers.