L20b volvo loader. Deutz 4 cylinder d3d engine non turbo. Starts good but at initial throttle up it hesitates for the first few rpms and then above around 15% throttle it runs smooth and strong all the way. Definitely worse when cold. Sometimes will go away completely when running for a few hours but randomly comes back. Basically no smoke. At hesitation if you look very close a very small puff of black smoke but almost nothing
Your stumble, is that when you're in travel or just sitting there in neutral?