Riding home from the dealership on my newly acquired '91 FLSTC, as the main supply was about used up, the engine started to lose power, missfire and sputter as it should. Engine performance didn't get any better on the reserve, so I suspected an electrical short in the ignition. I pulled over and looked for anything obvious, and I visually checked the fuel level which seemed okay. I switched the fuel valve back to main and pressed on until I got more pronounced signs of fuel starvation, switched to reserve and rode onto my fuel stop. It still ran rough and acted like it was losing power. I assume she was stored for the winter with less than a full tank so the gas may have some water from condensation. I gave her 3oz of Sea Foam just in case. Am I on the right track, or should I suspect something more sinister?

I also have a question on fueling. This is my first HD with a stock OEM tank. My previous bike had a custom tank. Is it necessary to fill both sides, or only the right and let the cross-fill do its job? It's very easy to over-fill the tank and the extra gas gushes from the left cap. I can't seem to get the level right by filling both sides. Looking for "the trick".

 

I would say that dose of SEAFOAM will clear things up. Give it a chance to work it's magic....

 

You'll need to fill both sides of that tank too.

 

the gas cap on the right has a vent in it / the left does not because of the kickstand angle - and if its clogged the cap vent or the PO had dropped it and dis lodged the stopper then the fuel tank is not venting and that will cause fuel starve -- jz

 

That brings up another question. Which is the vented cap; the one with the smooth edge or knurled edge?

 

the gas cap on the right has a vent in it / the left does not because of the kickstand angle

 

If it is newly acquired, I would go ahead and change out the filter screen in the bottom of the tank. Remove the fuel valve and the screen is attached to it.

 

Okay, got it. I just wanted to make sure that I didn't have something else going on here. The left cap doesn't seal and allows overflow. I was starting to think that someone had put another brands vented cap on it.

 

Kinda sounds like the caps aren't correct, or the gasket is shot on the left. And you might have a piece of trash in the fuel system somewhere. I'd clean the tanks and the filter screen out.

 

It could be you need a new gasket.
If you have a stock petcock take it off and get a Pingle.