Hi Kats: Off hand, I do not believe that a smaller diameter output tube on the L20 tank, would by itself have an adverse effect on the triple carb set up on your S20. A smaller output tube running from the tank to the electric fuel pump, combined with a fuel pump that was weak {or under performing} - could certainly adversely effect the performance of the S20. The triple carb's need to be feed fuel to their fuel input line at 2.5 to 3 psi. The size of their {the carbs} fuel input , combined with the fuel pressure specified - determines the total volume of fuel needed to keep their float bowls full. As long as the electric fuel pump at the tank, could provide enough fuel to keep the 432 fuel lines at the engine pressurized at 2.5 to 3 psi - - the engine should perform to specification. If the electric fuel pump was not able to maintain a fuel line pressure of 2.5 to 3 psi - - then the S20 engine would not perform to spec. Using a fuel line out of the tank to the fuel pump - one size smaller than needed would make the fuel pump work harder, but it should have been able to overcome the minor restriction and still supply enough volume to maintain the needed 2.5 to 3 psi - on the output side of the pump. It is possible that the fuel pump simply did not have enough margin or performance range {ie it just wasn't strong enough} to supply the needed volume of fuel at full throttle. Tthe only way you would know for sure if the pump was supplying enough fuel - is if you had a fuel pressure gauge in line with the carb's - that you could see while making a full throttle run. Second way of telling would have been to make a full throttle run with the car - then pull the spark plugs and see if they were indicating a lean mixture. Third way of telling would have been to install a wide-band CO2 probe in exhaust system - hooked to an Air/Fuel Meter. At any rate it sounds like you have already solved the problem - even if we don't know for certain what caused it. The pictures of the fuel tank are very interesting, and it looks like the shop did a great job. Thanks for sending them along. Interesting to see that the shop cut an access hole in the top of the tank, then welded it back up. FWIW, Carl B.