and sorry for this late reply.
September is a bit late in the season, or actually off-season. Many points of touristic interest are either closed, or have limited opening hours. For example the great Archipelago Ring Road is not doable anymore in September, because the key ferry connection between Houtskär and Iniö stops running on 27th August, and the shorter version (ferry Nauvo-Seili) will probably be on a reduced schedule if not shut down for the year, too.
The weather is probably okay for motorcycling (could even be sunny, dead calm and 20+, as e.g. last year around 10th September still
), maybe 15 to 20 degrees, but clear nights can be rather chilly (single digit temperatures). It usually is windier and rainier than in summer, with the first autumn storms. You`ll need to reserve some warm clothing if you plan to ride into the evening/night hours. Also, daylight is shortening by 6-7 minutes per day (!) by that time of the year... you can almost notice how fast winter is approaching. Another point, as many people are back in their daily grind (work, studies) by September, is that there are not many riding companions to be found. High season (and the best chance to catch sunny warm/hot summer days) would be from early July to mid-August.
As for the King`s Road, it has some nice stretches... but again, many places of interest will probably be closed in September. While there`s less traffic on these small roads, quite perfect for a small motorcycle (I myself prefer my easy-going 125cc Honda Shadow for leisurely summer tours, but a 250cc is sprightlier), you will make slow progress if/when you visit the sights, the asphalt on some stretches could be in bad repair. Known motorcyclists` favorites like the rollercoaster between Hamina-Virojoki at the eastern end of the King`s Road have very low limits (60 km/h) and heavy police surveillance. I think I saw 3-4 police patrols on that rather short (50km something) bit when I rode it one fine summer evening.
There`s also the Grand Postal Route all the way from Stockholm via Grisslehamn over to Eckerö on Åland, from where it goes via the Northern Route to mainland Finland. I`d say it is quite time-consuming to go island-hopping from Sweden via Åland to Finland, and surely more expensive than taking the big ferry Stockholm-Turku. I did that route westwards with a friend in 2012: pricing is such that you are persuaded to spend a night on the islands (not Åland itself) to avoid a surcharge on the ferry tickets, and you`d need two days for the trip from Sweden to Finland anyway (or rather three, if you`d like to tour Åland which is a nice place). I`ll add a link to the "Skärgardsguiden" guidebook just in case you`re interested, as there are many alternative ferry routes through the archipelago, too.
Did you plan to camp, or stay at hostels/hotels? Again, the weather isn`t that nice anymore in September (windier, more rain than in the summer season), many summer hostels/small hotels/guesthouses will have closed. You`d have to spend your time in cities if you hope to "meet the locals"
There`s also the obvious question what kind of places interest you, as there is an abundance of funny or quirky POI`s. How much time/kilometres are you planning to put into your visit? Finland may look small on a map... but it isn`t: you`ll have to see much road
I`ll add the link for the St. Peter Line in case you`d like to take that cruise to St.Petersburg (visa-free but rather expensive unless you find an offer), without your bike though. Please feel free to ask if you need somebody to find links and info - I speak English and German fluently, my spoken French is a bit rusty... but my Dutch is really bad
I`m not trying to dissuade you (
) but this just to prevent you from being disappointed.
Here are some links which could be useful:
* Touristic sites:https://en.wikivoyage.org/wiki/King%27s_Road_(Finland
)#Q219015 (King`s Road, ENG)https://en.wikivoyage.org/wiki/Archipelago_Sea
(Archipelago Sea, ENG)http://www.alandstrafiken.ax/en
(Visit Åland, Bicycle/MC, ENG)http://www.saaristonrengastie.fi/en/con ... lago-trail
(The Archipelago Trail ENG)http://www.nationalparks.fi/en/archipelagonp
[Nationalparks, Archipelago Natural Parl, ENG)http://www.finlandseaside.com/
(Destination Finland Seaside ENG)https://www.visitsouthcoastfinland.fi/en/
(Tourist Info South Coast, ENG)http://www.discoveringfinland.com/west-coast/
(Discovering Finland / W Coast & others, ENG)https://stpeterline.com/
* Motoring sites:http://www.tfmk.com/
(Touring Finlandia MC, FIN, Facebook)https://www.autoliitto.fi/en
[Automobile and Touring Club Finland, ENG) & Bookshop (FIN/SWE)http://www.bestbikingroads.com/motorcyc ... _3350.html
(Best Biking Roads, ENG)
There are some nice motorcycling route descriptions with pictures (in Finnish... I don`t know how well Google Chrome translates them) in this forum in the topic below:viewtopic.php?f=5&t=83102