Check the Valve
guides for wear (the most likely reason for smoking on start up) when inspecting the valves, Valve
seats, retainers, rockers, rocker-shafts, & cam-shafts for wear or damage.
The valves and springs should be replaced as a matter of course, the other items depends on their condition - if you are in any doubt, then replacement with new parts is probably the best course of action.
Other related parts you may wish to consider:
Add as many new parts as you wish to the same shopping cart, new Valve stem seals 12209MB9003 & retention cotters 14781551000 for example, and still only pay the same single fixed price shipping cost. Please be aware that this component may have other applications on other Honda machinery, so always check the part-number is right for your model prior to ordering. Pro-workshop gasket sealant 08C70K0234M easy to apply with perfect results.