Is there a way to advance/retard the spark timing on these beasties?
I believe you have the same ignition as the GL's that I am familiar with. Timing is adjusted by rotating the pickup assembly plate on the rear of the camshaft. Usually you never have to adjust this after inital setup as there are no parts to wear. You have limited ability to play with it as is since they are already close to the maximum advance the camshaft geometry will allow. On the 650's the starter often has a hard time turning over the motor on startup because of preignition. A lot of the starter problems, in particular the slippery starter clutch are caused by premature ignition.
There was a modification of the automatic advance mechanism that was published on the French site that allowed for more advance at high speed without low speed preignition problems that you might want to try if you are trying to get more out of your machine at high RPMs. although it may be limited. The current advance mechnism reaches its maximum advance at 3500 rpm.
I have experienced a direct link with the timing and the starter. On one of my 650 rebuilds, I had problem starting the motor with it stalling on what seemed like Top Dead Center. Changed the starter to no avail. Checked timing and voila! I like to set timing as far ahead as possible, possibly under the false impression that it helps performance, so I still get the occasional hesitation on the starter when I start up the motor on a warm day after a good workout.
You do not want to play too much wiht advance timing. I remember being stranded with my CL350 a few decades ago because of a blown out piston while riding on the highway. I had set the timing for more advance and it was too much for the motor. I sorta knew there was too much advance on it because it would kick back occasionally on the kick starter when starting hot! The same happens with the 650 except the starter takes it instead of my leg.
As for cooler or hotter plugs, Nolavox, if you put more advance on the timing, your motor will run hotter and I believe cooler(higher heat number?) plugs may be in order, particularly in your neck of the woods, but you may have to play with it. If you use a cooler plug, it may prove a little finnicky on cold starts but should run fine the rest of the time anyway. The user manuals already allow for cooler plugs (DPR9 is described as best for long highway hauls), and there are several high tech ones available now (platimum, iridium etc.) I have had a set of platimums in my GL650 for close to 100k km now with good success.
I sorta knew there was too much advance on it because it would kick back occasionally on the kick starter when starting hot! The same happens with the 650 except the starter takes it instead of my leg.
A colder plug will not change when it fires, the heat range of a plug has to do with at what temperature range it will effectively self-clean the carbon reside off the insulator that's left behind after combustion. You only use a colder plug when the engine is going to be operated under a fairly heavy load most of the time, a hotter one if your riving is virtually all stop and go or it's very cold outside.I wanted to ask if you think that going to cooler range plug might help w pre-ignition issues ? I'm afraid of leaning out and blowing up the way things are and I'm not going to screw with it's finicky air management/ Exhaust systems nor timing until I can get a better handle on it.