From Tobermory take the B8073 toward Dervaig then depending on how far you want to go you can follow this road right round to the junction of the B8035, turn left to Salen and then back to Tobermory. Or, from Dervaig there is an unclassified road on the left that follows the Glen and then goes through the forest. This road comes out north of Salen. OS landranger map 47 shows the northern part of the island. I was up there ten years ago. It is a lovely place.
I would say the full circuit of Isle Of Mull from the Craignure. Take the road towards Iona, take the B8035 all the way round to the B8074 which you follows over to Calgary, Dervaig and Tobermory. From there, the ferry from Tobermory or the coastal road down to Fishnish or Craignure again.
Alternative, and I have done this route myself, is the road from Craignure to Salen, the B8035 to the crossroad to B8074 and then follow this road over Calgary and Dervaig to Tobermory. It is an absolute fantastic ride with some medium to big hills on single track roads. Dervaig to Tobermory with the twin peaks was a killer.
This ride is in my top five of my best ever rides.
Once you roll off the ferry in Craignure, follow the coast north east to Salen. Then pick up the cycle track that goes through Salen Forest and beside Loch Frisa (keep your eyes peeled for Sea Eagles above the trees). Turn left on a quiet road and spend a few hours picnicking on the delightful Calgary Bay. Then follow round past Loch Tuath and Ulva. There is a basic campsite at Fidden farm or you may prefer to wild camp a little further on (with the sheep for neighbours).
Wake up, pack up and cycle. Those with more time on their hands will follow the road out to Iona, whereas those constrained to a weekend will head back around to Craignure through Glen More. If there is time to kill before your ferry home, pop out and see Duart Castle.
I agree with all that's been said, all of it, I don't think you can go wrong. Just make sure you have a days supplies going round the West coast, there's nothing there except scenery!
A night on Iona was the highlight of last year's trip, the hostel is one of the best I've stayed at, certainly in terms of location.
How are you getting there?. The popular crossing in to Craignure, there is an alternative, Lochaline to Fishnish. If you're traveling by train, the 40 mile ride from Fort William to Lochaline is as lovely and quiet as on Mull. Decent trains to Fort William from Glasgow, just make sure you book the bikes. Or go on the sleeper and get an extra days holiday!
A few photos to wet your appetite; http://www.derbyctc.org.uk/pictures/scotland/
Hmm ... I will be staying near Oban this September and I will be taking a bike up with me. It looks like it would only be about £11 for a day return on the ferry to Mull with my bike so if the weather is ok, I will definitely do the 140 km circuit!
The Scottish side of my family came originally from Mull but I have never been there. I think it is time to put that right ...