The RIV equipment for dynamic IP timing evaluation is expensive if still available. An option is to get one of those clamp-on inductive injection pulse sensors coupled with a timing light to determine whether the timer is operating to spec. Another option is to try a known good IP timer. The timer isn't difficult to replace. Removing the vacuum pump and chain tensioner gives you all the access you need. Maybe you can tell by inspection that it's bad but you have to remove it to see the workings on the hidden side.

However, if you have exhaust smoke as it is, you're either burning oil or getting too much fuel. I hesitate to suggest tweaking the full load stop if you're already heavy on fuel.

Sixto
87 300D