I've recently got an F78 fourtrak with 77k on a T plate to replace a similar D plate with double the miles.

Although the new one is very tidy and seems to have been well looked after, I think the engine runs a bit rougher and doesn't have quite the torque at low revs of the old one. It seems to need more welly when towing 1700 kg or so of horse and trailer. I don't have much experience with diesels (*lots* of experience with old/cheap petrol vehicles, but that's another story).

It sailed through its emission check at the last MOT, but does anyone have any suggestions about what I should be investigating?

Thanks in advance