Strange Fuel Issue

1985 XJ700N. Coming in to work today the bike started acting like it was running out of fuel about 13 miles down the road, and then it did. The low fuel light was not on, and the bike had 78 miles since the last fillup. I usually get in the high 90s before hitting reserve. When it would not start, I moved the selector to reserve and after cranking over a few times it started and I had no other issues. I stopped at a gas station about a mile down the road and it took 1.86 gallons to fill, so apparently it had not gotten to the reserve required level. The bike had been sitting for about three weeks, so before starting it this morning I set the selector to Prime for about a minute and then to Run when it started. Other than that nothing was different than in the past. It does have an inline fuel filter. Any ideas what might be going on?

 

is the vacuum line to the petcock ok, could it have a kink or an air leak, that could give the symptoms you describe, although starting it the second time then setting it to Run, seems to discount that

 

When I get home tonight I plan to take a close look at the vacuum and fuel lines. After restarting it I left it on Reserve, not Run. On the way home I plan on switching it back to Run and see if the problem reoccurs.

 

If it happens again, try opening the gas cap and see if that resolves it. If the cap has a clogged vent, over time it can create a vacuum in the tank and fuel will stop flowing until you let in more air. If it starts up again after opening the cap, check the vent hole for obstruction.

 

Good point. I'll do that if it happens again.

 

No problem on the drive home. But I am concerned about a possible vent block in the fuel cap. Is there a thread on repairing the fuel cap.

 

Not certain this covers all models

https://www.xj4ever.com/gas cap.pdf

Found here:

https://www.xj4ever.com/downloads.html

 

If your XJ700 bike is a CALIFORNIA model, then the gas cap is NOT vented, the venting goes thru the fuel tank and the "vapor cannister" and to atmosphere. If it's a 49-state (iow, not a Cali model), then the venting is thru the gas cap.