1981 xj750 backfires and has low-power when gas tank is full

I just bought this bike a few weeks ago and when i fill the gas tank the bike backfires, and has low power. it also smells rich. what would this be caused by and whats the simplest way to fix it? thanks guys

Clay

 

if it only happens with a full tank of gas it's possible that the vent line in the tank is bent down under the gas level, creates a vacuum and starves the carbs...had the same problem in my XJ550 a few yrs ago, got a pair of needle nose pliers, bent it back up in place and never had any problems after

 

When the problem happens open the gas cap and see if the problem goes away. If so remove your gas cap and take the scews out and look at the little check ball and see if it is all crudded up with old gas. If the vent is plugged it will act like you have described. Clean and see if that helps. Sounds like its running out of gas. The tank needs air to breathe and let the gas flow freely. Hope this helps. Good Luck

 

Re: 1981 xj750 backfires and has low-power when gas tank is

forgot about the vent in the cap... mine has a tube inside the tank too for some reason!

 

that makes sense, cuz the way it acts is the same as when it ran out of gas a few weeks ago. althought it still has the rich smell, regardless of how it is running. although I'm pretty dang sure that i need to clean the carbs. sadly I can't do that here at college so i'll have to wait for a month or so to take it home.

 

Bummer. Ever thought of venturing over to a buddies place for the day and working on it there? I've attended a few wrenching sessions in my days. Heck, I've swapped labor on a ladie's bug to have use of her driveway for a weekend. If you have the desire, a way will make itself apparent.

 

Is there any schedules for the "wrenching sessions" in MN? It would be of great benefit and I would definately try to attend.