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1977 911S Poor Performance Over 4000 RPM


Vehicle Information: Model: 911s; Year: 1977; Body Type: Targa; Total Mileage: 77k;

My car runs strong at full throttle until it reaches about 4000 rpm; itthen begins to spark knock and performance 'falls off'. It is very hardto reach 6500rpm in 2nd, 3rd, 4th gear as it seems to take a long time (Ihave owned serveral 911's and I am very familiar with what theperformance should be). The factory calls for the timing to be set at TDCat idle, and I actually have it retarded approx 3-5 degrees to reduce thespark knock. I have had the distributor checked and rebuilt, newpermatune CD and coil, and new ignition wires. Compression is approx 150on all 6 cylinders, and I have just completed adjusting the valves andreplacing the chain tensioners. My original thoughts were that thewarm-up regulator was at fault, and not suppling the additionalenrichment at full throttle (which is exactly what it feels like isoccurring). So I replaced the warm-up regulator this weekend. No changein performance, but the car does start much easier hot. My next thoughtis to replace the sleeves that the injectors slide into, as I have heardthey are plastic and have an 'O' ring in addition to the regular biginjector 'O' rings which I just replaced. Any Ideas?

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