Graph shows road network and my aim is to create 9000 loop route. For that we can explore all nodes that 'slightly' further away than 4500 m. So pick one and find best route to it from START:

Backup and temporarily remove edges of that route from the graph and recalculate best route between same 2 nodes:

Merge new route with backup to store first computed option (9800 m total, so 4000 m threshold was too high!):

Restore edges, repeat with next candidate. Note if your START-FINISH node is dangling, removing edges won't work. So simply increase weight of travelled edges significantly (this is what I called make edges very heavy).

Graph shows road network and my aim is to create 9000 loop route. For that we can explore all nodes that 'slightly' further away than 4500 m. So pick one and find best route to it from START:

Backup and temporarily remove edges of that route from the graph and recalculate best route between same 2 nodes:

Merge new route with backup to store first computed option (9800 m total, so 4000 m threshold was too high!):

Restore edges, repeat with next candidate. Note if your START-FINISH node is dangling, removing edges won't work. So simply increase weight of travelled edges significantly (this is what I called make edges very heavy).

See also Creating laps... post