[L8apex32]

1981 911SC euro, stock engine, high miles, stock racing class use only

The engine is running lean in cylinders 1, 2 and 3. You can see the white deposit on the exhaust pipes and the spark plugs, left side only. My mechanic put it on the dyno to analyze air/fuel ratio and to diagnose. He found that moving the fuel lines - hard lines between the fuel distributor to the injectors - from cylinders (1, 2, 3) to (4, 5, 6) and vice-versa moved the lean condition from the 1, 2, 3 side to the 4, 5, 6 side of the engine. It has true dual exhaust, no cross over, so the analyzer sees one side or the other. That seems like a pretty good diagnosis. But, is there anything else it could be?

I have two further subjects to ask about. Before the most current diagnosis, my mechanic proposed that it may be brake related in that the vacuum line to the brake booster comes from the left side of the engine. Could a leak in the vacuum line to the brake booster make the 1, 2, 3 cylinders go lean and not 4, 5 and 6? (I did feel my brake feel rock hard during a double yellow, which indicates a loss of vacuum to the brake booster.)

Finally, it seems that all 3 cylinders are lean on the left side. Is there anything in the fuel distributor that would affect 3 cylinders at once on the same side?

Similarly, is there anything in the air intake path that could mess with cylinders 1, 2 and 3 but not 4, 5 and 6?

Thanks.