912 running rough

[Dailey100]

Hello

My 69 912 had its bottom end rebuilt, we added new weber 40s and we just finished a 1k mile break in of driving the car mildly at the 4500 range, we increased to 5000 rpm's after 600 miles and now started driving normally(spirited).

The car has been running great and strong, this morning wasn't any different until the car decided to idle super rough at a stop, i killed the car launching in first because it had no guts. I started the car back up and nursed it with a heavy clutch/gas combo the four blocks home. When I got home i cleaned up/out the distributor cap (seem oily) after the car sat for about 10 minutes I started it back up and it was idling normal and drove great for a 1/2 mile, then the car would not go faster or climb higher than 4k rpm in third gear, after i came to a stop the rough idle came back.

the funniest part is, after the car sits a few minutes off, it will start right up and idle perfect only to repeat the issue after reaching third gear 4000k rpm.

Any guesses whats going on? (new to porsches/VW's)

[upwardr]

Sounds like a fuel delivery problem. Maybe the vent for the tank is plugged. Try and loosen the gas cap when this happens and see if it improves.

Check fuel pressure, I have a 356 With this same problem.

[Dailey100]

Thx...I will give that a try, I put a new gas tank in 1k miles ago and there is still tape over the vent. This would be the first time that was an issue but that's a good place begin.

Thank you,

[Dailey100]

So I drove it with no gas cap and it seemed perfect, drove it a few times with no issue. Then it did it again, I took the tape of the breather installed some too thin PVC and it didnt run better. I have had some electrical sorted out recently could some thing came loose, could that cause these issues?

It seems to run great after it sits over night. Then after a few drives gets bad. Also after a brief period of being off, 10 mins or so it will drive good for a min or so and the bad?

Basically I also would point to a poor fuel delivery - did you check the fuel filter in the tank outlet- but as you say that the problem occurs at around 4.000 rpm, the ignition also could be the cause of your problem. What about the coil? Sure it's OK? Distributor advance sticking when warm?

Please tell us some more about the engine. Ignition type, carb jetting and so on. What kind of electrical issues did you recently have? Even a bad cable from the coil to the distributor could be the cause, although not very likely.

Otto