Rough running, backfire, then no-start... eep.

[exc911ence]

Last Saturday, I had the Targa out for the day and it was running pretty well. By mid-afternoon it had started running rough and popping back through the carbs but it still ran. By the evening, it idled fine but would barely accelerate, hiccuping and backfiring the whole time... I barely got it home. I had assumed it was a carb problem (has Webers) but now I'm leaning towards an ignition failure.

Today I pulled all of the plugs and found 4 of the 6 fouled. I cleaned them up and reinstalled them. I then inspected the cap/rotor/points but they all appeared fine with minimal wear on the contacts. Afterwards, I was able to start it OK and it idled smoothly in the driveway for about 5 minutes. After the 5 minute mark the idle speed dropped and it started popping and farting out of the carbs and exhaust again. I jumped in and gave it a couple of shots of the accelerator to keep it running which caused some serious missing and finally a huge gunshot-quality backfire out of the muffler which stalled the engine. After that, the car wouldn't restart so I pushed it into the garage and pulled a sheet over its head.

Anyone have any ideas? Ignition coil perhaps? CDI box? Help!

[anger710]

Hey Dave

Sounds similar to my 73E with mfi woes. Mine seem to be mostly fuel problems. Clogged fuel tank screen, Tired fuel pump, Bad fuel lines, Older main fuel filter. Some of them are related to ethanol in fuel and sitting over winter.

Tom

[kach22i]

Check the points more closely and maybe replace the cap and rotor.

Check your list twice just like Santa Claus, you will find out who is naughty and nice.

[kach22i]

I've been thinking about this, check under the distributor cap, is there moisture on the underside?

Also try replacing the red cap fuel relay up front, it can act funny from wear and age too.

[exc911ence]

Cap was clean and dry inside but I plan on digging into it again on the weekend.

I'd say it's getting plenty of fuel from the fouled plugs and rich, eye-burning smoke coming out of the exhaust.

Worst case, it gets floated over to my favourite mechanic if I can't figure it out. I hate having the car out of commission with summer being so short here. Glad I have my motorcycles to keep me from going completely nuts!

[krobb]

Maybe this is a little late but it may be useful to others:
I had a very similar experience with my 1970 911. It was spitting and backfiring pretty loud one day as I drove it. All of a sudden, a huge backfire occurred and the car died. It would not start afterward either so I examined the cap, rotor, plugs, wires, ignition box etc and no sign of a problem. I checked everything 3 times or more and found nothing. I finally took a look at the points and found the gap was way off. After setting the gap again, I had no problems. It started right up again and ran great. I have since gone to the Pertronics ignitor which works nice but from what I hear, they can burn out. If you have points, take a look at the gap and dwell, it might save some frustration.

[JJ 911SC]

Originally Posted by exc911ence

Cap was clean and dry inside but I plan on digging into it again on the weekend.

I'd say it's getting plenty of fuel from the fouled plugs and rich, eye-burning smoke coming out of the exhaust.

Worst case, it gets floated over to my favorite mechanic if I can't figure it out. I hate having the car out of commission with summer being so short here. Glad I have my motorcycles to keep me from going completely nuts!

Dave

You must be in the East end as we did not have a summer in the West end... lol. 32F outside as I type this.

Who is you favorite mechanic/shop?

J.J.