Quote Originally Posted by Austinsjeep
It could be a 2.5 (they look the same externally), but I think I am right in saying the first couple years production of 110/90 used the 2.25. It is the original engine...
Easy enough to tell the two engines apart. The 2.25 has the distributor pump mounted vertically on the side of the engine where the distributor would be on the petrol 2.25. The 2.5 has the distributor pump closer to the front of the engine and it is run by the timing belt. The front timing cover on the 2.5 is therefore much larger.

Brett