I've recently experienced some strange and intermittent fueling behavior.
When the tank is relatively low, like three bars or less, the engine will momentarily bog down under sudden heavy throttle, almost like it was running out of gas, but the tank was not empty. Gradually rolling on the throttle is fine. Filling the tank resolves the problem, but it's not yet clear if it's a fuel level thing or just relieving built up pressure due to clogged vents. The vent tubes all seem to be in place, but I have not yet removed the tank to see what lies beneath.
The bike was a rescue after sitting for unknown years. The tank does not have any sludge in it, but the filter and pump are probably the original.
I'll plan to empty the tank and replace the filter, but should I look for anything else? The pump seems to work fine, except the weird fueling at low levels.
The bike has the stock airbox. I replaced an airbox hackjob by some previous owner. there are no indications of flashes or mods.
It *probably* still has the fuel vapor recovery system in place since I can see the pressure valve attached to the vent tube coming from the fuel opening. It's possible someone messed with that system, given other mods that were done and indications that someone took the tank off previously.
The fuel cap flange spacer is in place with a tiny opening near the vent barb. See pic.
Any suggestions beyond "open the cap perdiocially"? That's one likely easy fix, but I'd rather understand and fix the underlying issue.
