I read that these fuel additives clean the intake valves but not the exhaust valves. Since the problem lies in the exhaust valves I'm concerned that this will not do anything.
Can I remove the header and spray some Yamaha Ring Free directly on to the exhaust valves?
Thanks for the assistance.
Well, you're partly correct. The correct part is that when used as a fuel additive, these kinds of compounds (which are almost all virtually the same as "Techroline", BTW) don't get a chance to do anything to the exhaust valves. Thus, the "soak and shutdown" technique I described. And yes, you could squirt some directly on the exhausts. Be careful of getting too much fluid into the cylinder.
However, the likelihood is greater that it's an intake doing this. If so, the carbon causing the problem will be deposited in one of two locations; either around the outer edge of the valve near the point where the valve face and the seat meet each other, or on the stem where the end of the guide is when the valve is closed. It will probably be heavier on the two outside valves, since more fuel runs up the center than the outer ports. You may be able to remove the carb and pick this off using something like dental picks (with the valves closed) and blow out the pieces with air. The engine can digest very small pieces of carbon without a problem as long as you get most of them.