81 911 SC - Sometimes she starts, sometimes she wont..puzzled I am.

[selliott58]

So here is my issue and I hope someone can aid. I have done a bit of searching but hope this can narrow it down a bit.

1981 911 SC

Sometime back after a normal drive, pulled into the garage and shut her off. Went out a few days later and the car would not fire. For that matter not even a hiccup. It would however turn and turn but no hope of starting. Took off for business for a couple weeks, came back and figured before digging in or towing to the mechanic I would try on more time. This time...I got a hiccup. Kept the throttle depressed and after about twenty starter revolutions it fired with a large belch of smoke, ran rough for about thirty seconds then smoothed out. Took it to my mechanic as I was baffled and he could find nothing wrong. He drove it for half a tank of gas and no issues.

One month later. A quick drive to the grocery store. Stopped for a few hours, climbed back in and ten blocks to the hardware store. 5 minutes inside, and once again, she wont start. Turns until hell wont have it but not even a belch or hiccup. Since I was on an incline I figured I'd coast home, and while I was at it try to compression start it. No joy.

This morning, still wouldn't start and as this is getting beyond my pay grade, decided to have them look at it when it was not starting in hope of re-creating the issue. As soon as it rolled off the flatbed, vroom. I am confused and so is the mechanic. I do a fair whack of the work on this myself, but this one has me stumped.

It does have a perma tune ignition system, but other than that no mods.

Any thoughts would truly be appreciated

[911freek]

Do you have a pop-up valve installed? It may not close properly after it pops. If no valve, the airbox is famous for cracking on backfires.

If its a fuel issue - depressing the throttle will do nothing because that is air you are pushing in, the system works on Vacum.

Next time I suggest you take out the air filter, and nudge the shelf under the airfilter cover (far end right side) with the switch open. You should hear a hum/buz/erotic whisper (depends on teh listener, really :-) and then try to start the car again.

If it starts, you might be having vacum or fuel regulation issues.

[selliott58]

I will indeed listen for that erotic whisper....which if heard will be far better than the " I have a headache" that I have been hearing as of late...