For any continental rider (UK included!) everything is different in Corsica. First of all, it's useless to schedule your trips based on the average kilometer you want to do during the day, roads here, even new rebuilded, do not allow hight average speed and anyway if you come here with the idea of speed reccord, you are at the wrong place and will miss the magic side of the island. Second point is, if you increase your speed to much, you gonna face big dangers which are: Large vehicles on the wrong side in the curve, animals (veals, cows (without cowboys), pigs..BTW there almost no more pigs on the road since a couple of years) standing or sleeeping on the road,  sudden changes in the tarmac condition (becoming narrow, holes, stones, sand...notice that this years the global road network in Corsica has been much improved). And you will probably quite often be charmed by the marvellous and changing landscape. So, for the average speed you should better estimate a 50 to 60 km/h and some more time for gastronomy.
Along the road it's quit easy to find gas-station compared to some place on the continent but when you see the price of the precious liquid (even with lower taxe rate) you understand why(almost)! For your info, there is no supermarket gas station in Corsica.

When to come?
The best period for a motorcycle riding is 15 of mai to 15 july. Nice weather, nature at it's top, low crowded and lots of accomodations vacancies.
Another interresting period in september, the sea is still warm for the morning or evening bath, it is low crowded, thunderstorms are not to present but vegetation is burned by the summer sun (color changed, beauty stays).
If you cannot avoid the 14/07 to 31/08 period you should prefer the inner area of the island.

Remember: Except the sea side, Corsica has mainly a mountain type climat , for which it is very difficult to do forecast . You should understand that the restriction i made are for the time period before mai and after september are specific to constraint of the motorcyclists way of life that we very much know...Out of that let's go for it!
Ora Ghjé!
Little advise:
If you arrive to Corsica with the Ferry (you could also come with plane and rent a motorbike) i very much advise you to follow i favourite way to arrive and leave the island.
1/ For the arrival, where i get the best emotion, it is to arrive in the early morning (on a sunday it's even better) in Bastia. Because first of all the Feery will end the trip navigating along the "Cap Corse" and this start the emotion, then you land in the north of Bastia, still asleep, but in an atmosphere like nowhere. From there you will start the Cap Corse Tour, some says it is a summary of Corsica, I only say here your emotion will grow up immediatly!
2/Almost every thing has an end, that's a good reason to take a last great tast on the way back home and leave Corsica with the ferry (The Monte d'Oro) from Porto Vecchio to Marseille. It's not a ferry like the other, there are less passengers and she turn round the south side of Corsica through the "Bouche de Bonifacio", the Ferry generaly (and the Command try to make it so) is in front of the cliff of Bonifacio during the end of the afternoon. With that last shot you will be sure of one thing: You will be back soon.

Make yourself a taste with some pictures

Here is a list of "Gîte d'Etape" in Corsica

Corsica #1 ** : Starting from Evisa, quiet village in the fresh mountain air, a very nice camping placefor the tents lovers. Way down to the Spéluncato Canyon, riding through the famous Calanches de Piana, Cagèse and the splendid outback between Ajaccio and Vico.
Corsica #2 *** : Starting from Aleria on the east cost 80km south of Bastia.The good thing here, is can have the choice for several trips starting from this point and you will find a nice camping just on the sea side and away from the main road. The first trip will lead you to the "Castagniccia" area which is a marvellous place still away from the touristic invasion. Sure you will love it.
Corsica #3**: You will leave Aléria early (and happy), again, yes, but it is better. Today a 125km round trip and in the green mountains again with a final in the  Fiumorbo (i should write Fiumorbeautiful). The all trip on roads that you would normaly not have think to try and that are in a real good state.Please, do not hesitate to make breaks the little villages, near the cool  fountains, at the many points of view. Take care you will have a very nice day.
Corsica #4***: Leave Tattone under the Monte d'Oro to Vizzavone, you may have a coffee or breakfast at the "resto du chef de gare", but be aware that you have a long road to ride... Today again, 180 km, and always with lots of mountain and green country side, with a final in the "Col de Sorba" (Sorba pass), which is always so marvelous despite the fire it had a fiew years ago. Do not hesitate to have some stop in the small villages and at the fountains to refresh yourself and to take a look at the many panoramas. I bet you will have a nice day!
Corsica #5***: Today, the end of the Cap, a small trip with only 120km,but you will probably often stop for a little visit in the villages or a point of view, yes it is true, you will not believe your eyes!Macinaggio, Luri, Pino, Barretali, Canari, Morsiglia, Centuri, Ersa, Barcaggio, Tomino.