POP and smoke while setting ignition timing
 

Finishing up a head stud and leak repair on my 1980 911sc. I installed the distributor with cyl #1 at TDC, and I tried my best to line up the rotor with the notch on the distributor, but I noticed that no matter how many times I pulled it out and pushed the distributor back in, the rotor would end up cocked a few degrees away from the notch. I figured no big deal, I'll sort it out with the timing light when I start the engine up.

The engine fired up fine and ran fairly well, though I could see with my timing light that even with with the distributor rotated all the way counterclockwise and the end of the slot butted up against the mounting stud, the timing was slightly retarded I think (the 5 mark was at about 11 o'clock). I consulted with a mechanic friend of mine, who (unless I misunderstood him) told me to pull the distributor out, rotate the rotor a few degrees clockwise, and reinstall the distributor. So I did that.

Then, when I turned the key, it started cranking, started to fire up, and then I heard a very loud POP sound. I took the key out of the ignition, went back to look and I saw smoke rising up from somewhere underneath the airbox - I couldn't tell exactly where but it seemed like it was probably on the left side. The amount of smoke coming out dwindled over time, but it continued to smoke for several minutes.

I'm a total newbie when it comes to diagnosing issues - does anyone know what happened? What should my next step be?

When you pull the distributor out, you have to turn the rotor before pushing the distributor back in or you haven't changed anything.

Get the engine back to TDC with cyl #1 on the firing stroke. Then get the rotor lined up with the notch and with the timing adjustment in the middle of its rotation slot.

By turning the distributor clockwise (they spin counterclockwise in 1980), you advanced the timing. If you also left the timing slot butted up against the mounting stud, then you may have been way advanced. The plug fires when the intake is still open and you get a pop and smoke out of the intake.

Do you have a pop off valve under the air filter to protect the air box from this?

Ignition timing..........
 

TargaSC,

Let’s hope the backfire did not crack the airbox. BTW, I am in Carmel, CA just several miles from you. If you need some assistance, PM me your number and I will call you back.

Tony