I still own a 2500S and a Mk2 2.5 PI, which I've owned for nearly 25 years. Both low mileage, and original. Worlds apart in performance though. With the PI, being mechanical fuel injection, the engine settings have to be kept in perfect tune, the metering unit operating perfectly, the throttles butterflies perfectly balanced, but it is extremely powerful when in perfect tune, and returns good mpg - around 25 to 30 on a run, marginally better than the 2500S on carbs. The enjoyable response from heavy use of the throttle however reduces this figure down to around 18. But let the fuel pressure drop, incorrect vacuum, combined with overheating of the fuel pump due to low fuel levels (the fuel cools the pump with hot excess fuel returned to the tank), which then doesn't cool the pump sufficiently, consumption increases to horrendous figures,
and the pump always dies at the most inopportune moment. The fuel level has to kept at least half full to ensure there is sufficient cold fuel to cool the pump. But what a great classic to drive!
The 2500S has twin HS6 SUs, with nowhere near the performance, but very simple to maintain and keep running smoothly. The problem with these late models was the steel used in their construction was imported and of poor quality which has resulted in the majority corroding away in front of their owners eyes. The S is now one of the sought after models, along with the PI, which now exist in low numbers as they were unnecessarily scrapped or sold on early due to poor running issues and the lack of understanding of the PI system. Even Triumph dealers struggled with it.
I've driven a good number of classic cars, but none give as much pleasure as this range of Triumphs!