69 Skylark: Valve job advice.

[PPestorius]

Hi, I've got a 69 Skylark that's been blowing smoke at startup for years. Following a recent tune-up I'm back-firing like mad. I was pretty carfull while tuning the car, but perhaps I advanced the timing too much? I was never back-firing before. Pressure testing the engine shows that my 5 and 6 cylinders are weaker than the rest, but they're not terrible. They average out to about 65 psi.

It's been suggested to me that the heads are shot. It's easy for me to agree with this, but I'd like your advice.

The engine starts right up and sounds pretty good, but backfires immediately with any load.

While tuning I watched the valve train and used
a feeler to gauge exactly when #1 started to descend. That's what I'm callind TDC and my timing indicator is right on the mark.

Thanks for the advice.
P

[malc]

Hiya,
You may have more problems than you think. Those compression figures are really low, for a '69 350 they should be 160psi, with the 400 coming in at 170psi. According to Chilton, ignition timing should be set at TDC, with points dwell at 30', points gap at .016", and plug gap at .030". To be honest tho', with only 65psi, I think your ignition timing is the least of your engines problems,
Best of luck
Malc

[theoldguy]

The smoking problem is probably valve guides. I would suggest that if the backfiring started after the tune up, that you recheck the firing order. It is a simple thing to switch wires when reinstalling them, and might be the problem

[PPestorius]

...I made a mistake setting up the timing.
a big mistake. I'm running SUPER late. I know for sure that my values aren't great...but I think I can get some improvement.

I'll work on it this weekend and post an update. Thanks guys.

[PPestorius]

Still back firing and smelling gassy after double checking the timing setup. I'm gonna let a pro look at it and see what happens.

Sheesh.

[Bob]

Did you do the compression test before or after the valve adjustment?

If you did it after, maybe you over tightened the vavles, because that is pretty low!

You do set valves at TDC on the compression stroke. If you determine the TDC of a cylinder by watching the valve action, you may be watching the exhaust close and the intake open. If this is the cylinder you are adjusting, niether valve will be closed and bringing them into adjustment at this point will cause you to overtighten them and have low compression. Using this method of TDC identification you could adjust the cylinder in the opposite FIRING order.

Good luck