Have you measured the lobes, looking down the tappet port will only tell you so much. I have to be honest, I found my wife's XR2i to be slower and flatter than my K-Jet XR3i but the thing with CVHs is that they vary so much.

Best thing to do is get it on a rolling road, they can check the mixture all through the rev range and load and can then tell you what is going on with the engine. A lot more accurate than replacing bits in the hope that it sorts the problem.

One thing on those is the map sensor, they tend to go a bit wonky. Check that there are not any air leaks in any of the hoses as this could be upsetting things. What colour are the spark plugs and does the car drive well or does it hesitate a lot?

Breather pipe on the right side of the engine, remove from rocker cover and the block and check that it is clear