Tuning Webers

Hi

I recently changed fuels, from Super to a hi octane unleaded (98), prompted by the eventual phasing out of the availability of leaded petrol. As a result my 69T seems now to run a little richer and there is a slight drop in power despite the higher octane rating. Inside surface of the tail pipe is looking a little black.

I have recently started researching the workings of webers as I am very interested in learning how to tune them properly. Most of the books I have read (Haynes, Pat Braden) seem to focus on rebuilding and give little time to tuning so I am interested in any tips or procedures in obtaining a correct mix of fuel.

Thanks

My guess is you might have some luck at a local library looking for 1960s era books on carburetors, racing engine tuning, and the like ... part of a legacy of technological change is that jet reamers, gauges, and drills are still available, but the knowledge of their use is becoming lost! From the '69-'71 Spec. Book, your carburetors left the factory with 110 main jets and 185 air correction jets, while the '71 2.2 had 105 main jets and 170 air correction jets. My suggestion would be to try a set of the 105 main jets to see if that corrects the richness you are experiencing ... a 5 point change is about as small a change as you can make without going to reamers. If you could find a 'tuning shop' that happens to have a Porsche race car using Webers, you might be able to pick up some used jets at a reasonable price ... I suspect new jets will be priced like gold jewelry at a dealer! And, if larger jets are all you can find, they can always be soldered closed, redrilled a smaller size, and reamed out. Good Luck!

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Warren Hall
1973 911S Targa

I recently completed the task of rebuilding my Weber 40IDA3C carbs on my '70 911E. The process was far more simple than others($75/hr techs.) would like you to believe. I will begin tuning next week after I install the motor. Pat Braden has a good book on theory and tuning of Weber Carbs. I also used the Haynes which does have an OK section on tuning. If you'd like I can photocopy(with the permission of the publisher of course)the pertinent section and fax it to you.

As far as replacement parts go, use Richard at PMO(Porsche Mail Order) in CA. Phone is 562-401-3673 (PMO does not answer the phone) and the fax is 562-940-1905. Place your order via fax with part numbers,(from Haynes blow up) ship to, and Credit Card info. They process and ship same day. You can also fax him questions if you wish and he may call you back. It seems like a strange way to do business but I was very pleased with the end result. Good luck with it.

Rich

Warren, I’ll hunt down some new jets over the next couple of weeks, as per your suggestion. I am currently researching the process of the jet changeover before attempting.

Rich, I’d be interested to hear how you fair tuning upon installation. Even though my carbs were recently rebuilt at the expense of the PO, I was most interested in your comments regarding the difficulty of the rebuild process. Thanks for the offer to fax those pages but I think I have those books and I don’t think you’d appreciate the long distance telephone call charges to Australia. Good luck.

Regards

Having fond memories of Webers on a '67 S engine in my old 911 T I found that the most common problem with them was tiny particles that occasionally caught in the idle jets. It would cause a lean misfire at idle and lumpy performance on take away. Opening up the jet caps with the stubby screwdriver while the car idled usually indicated which of the jets was at fault. Removing it and clearing it with a air blow usjually did the trick. This little item can make you think the carb needs serious work but it's one example of looking for the simple and basic things first.

Thanks for the information. Regards