Intermittent smoke from 300tdi

Hoping someone has the answer as I am struggling, have a 110 (2000) with a reconditioned 300tdi (24k miles since recon) replacing the original TD5, vehicle pulls well no smoke on starting however after 10 minutes over 60mph when drop back to idle smokes badly. However, if I don’t exceed 50mph runs happily all day with no smoke. Both compression and leakage test are fine, oil level holding steady. Suspect over-fuelling but don’t if is injector or pump or both or something else altogether. Any insight would be appreciated thanks

Sounds like a bike I had, four carbs, after running 'enthusiastically' for a while, if you rolled off and slowed down a tad the exhaust smoked for a while. Never got to the bottom of it, but another mate reckoned it was something to do with the carb diaphragm/spring ... I'm wondering if there isn't something similar in the Injection Pump that keeps fuel flowing when you've asked it not to.

Thanks for quick reply and yes suspect pump, time to get it changed