So, I've been getting horrendous fuel mileage on my '04 Rockster (50 miles before the light comes on). Turns out that both top plugs are not firing. I've done lots of research on this site, and others. I ordered new (used) coils and they didn't work. There is a small possibility that all 4 coils in my possession are bad but I don't think that's a high likelihood. I don't have the technical knowledge to do a full electrical diagnosis.
Then I read about the stickcoils-ectomy. I didn't name it. Anyhoo, the person simply connected the bottom plugs to the top ones and called it a day. Went from dual spark to single spark but he says the bike runs like a champ.
Anyone done this? Thoughts?
You will be far better off repairing your stick coil problem than trying to make it a single spark engine.
It is a possibility that you have 4 bad stick coils but not that probable.
There is a good chance that your 04 bike has second (load relief) relay powering the upper spark plug coils.
So first thing, do as Roger suggests & check the green/black wires going to the upper coils with the engine running for 12 volts on those green/black wires.
If no 12v to the upper coils then that usually points to a power relay problem, or a power/ground problem TO that second load relief coil. Or a broken wire between the relay & the upper coils.
I have worked on very few Rocksters but 2nd load relief relay is usually in the center row of the fuse box on the L/H end. That relay needs full time battery 12v (no fuse) going to it (red wire) from battery (+) post. Needs full time ground going to it from battery (-) post.
The trigger circuit to that second relay is 12v direct (green wire) from ignition switch but that is the same circuit that runs the lower coil so it is probably working if the engine is now running on the lower spark plugs.
If your 04 is by chance a bike without the second load relief relay (really just a power relay) then the upper coils are powered by the same green wire that powers the lower spark plug single coil so that circuit must be working if the engine runs now, so if no 12v to the upper coils, it is probably just a simple broken wire or bad solder joint.
Pretty easy to at least see if your upper coils have 12v to them with engine running so do that first. If you find NO POWER to the green/black wires to the upper coils then post back & we can help you track the problem to it's root failure point.