1977 Porsche 911 3.0 Euro Engine Backfire and Warm Start Issues

[lynxer]

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[cool5]

I had a similar situation awhile back, also after a carb rebuild, it turned out to be a microscopic hole in one of the carb floats. The car ran great as long as you had your foot in it. It backfired and was sluggish in the midrange and after shutting it down the residual fuel pressure would over flow the bowl and into the engine resulting in hard starts.

[lynxer]

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[Josh D]

I'd get rid of that glass bodied fuel filter near the fuel pump PRONTO!

Also, what type of strap is that holding the fuel pump in place?

[lynxer]

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[Targalid]

Nick,
That your car starts easily when cold but is difficult to start when warm suggests an overly rich mixture. When the motor is hot the fuel vaporizes easily and will give a rich mixture but when cold the fuel is partially vaporized in the intake and acts leaner. Your description of setting the timing seems vague. Ignition settings are normally expressed in degrees relative to the Z1 mark. How many degrees of advance do you have at 4K rpm? What is the advance at idle? Have you looked at your spark plugs? I bet they are black from the overly rich mixture and your ignition timing is still not correct. Post your location so that someone local can give you a hand with some of these basic checks. You have a beautiful car. With a little knowledge and this forum you will have it running well.

[cool5]

Only a suggestion on the floats, I don't think I would go out and buy anything until you have done a little more diagnosis. In my case, after shutting down the engine and waiting a couple of minutes I could see raw fuel spilling down the throat of the carb.

[lynxer]

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