[Christien]

This is an issue that's been dogging me for a while now, and I'm getting sick of throwing time and money at the wrong things.

I'm getting a notable loss of power throughout the rpm band, but only when I've been driving the car hard at the track - it never crops up on the street. It starts just as my tires are getting warm, so after a lap or so. The car still accelerates and there's no stumbling or unevenness across the power band, but it feels like I'm down to maybe 75hp or something. The engine sounds perfectly normal, and if I pit and let the car cool down for 10 or 15 minutes, it'll drive normally for a lap or 2. The power lack is such that I can barely hold a steady speed on an uphill straightaway (Mosport) with the pedal to the floor, 3rd gear, 5000rpm.

Car is a 72 911T with original Zenith carbs, carbs were rebuilt 2 years ago (by me) and tuned professionally, brand new MSD coil, replaced CD box with blue Permatune used box, new plugs and plug wires summer of 2006, new points last summer, timing, advance, etc. all set by the shop when the carbs were tuned.

I've floated this problem here on Pelican before, but that was before the coil and CD box were changed, and that didn't fix it, even at a track day in cold weather (10C/50F). The only thing that gets rid of it is letting the car sit for 10 or 15 minutes. And again, this problem has never came up on the street, only at the track.

Any thoughts? My next step if I can't fix it will be to just take it into the shop for diagnosis, which I know will hurt my chequebook significantly!

Thanks!
Chris