|the source of the problem|
I started once again getting a vacuum in the tank. Last summer the problem was solved by rerouting the fuel breather hose (actually also a KTM recall issue) but this time the problem was elsewhere. I tried to fix the problem on the road by promptly cutting the breather hose in half as my assumption was that the hose was obstructed somewhere lower beyond where I could see. That did not fix the problem.
Blowing & sucking on the the remaining part of the hose revealed that the still attached part was not letting air through and the part that was cut off had no obstructions...
|troubleshooting on the road|
After some head scratching I noticed that something started moving inside the hose connection. I had the filler cap removed so I could see if something was coming out of the hose while I was blowing. Apparently there is a tiny valve inside the hose connection that had jammed shut for some reason. With furious blowing and sucking at the gas station pumps it seemed that the valve was cleared up.
The problem has not reappeared since, but I'm not going to wait for that. I will be installing an aftermarket fuel filler neck & cap as soon as possible.
I'm wondering if these valves and the resulting vacuum has something to do with the fuel pump problems the 690s seem to be having? Will the vacuum have a damaging effect on the fuel pump? Someone smarter than me have an opinion on this?