Is this vapor lock??? Wierd

[GTGS]

My 81 550L is acting wierd the day after a fill up. Here's whats going on. The bike has properly cleaned carbs, a sealed tank, brand new petcock and has been running very well. Last week I filled her up and rode it home. The next morning she ran fine and I rode for awhile. Parked it and got back on it a few hours later. It burbled once and then nothing. I choked it ,She cranked but wouldn't even try to start. I pulled the plugs and had spark but the plugs were dry. I pulled the gas cap and let it sit on prime for a few minutes and she fired up with the help of a jump start. It ran fine after that. No issues. Yesterday on the way to work I fiiled it up again. It ran fine for the rest of the day. This morning I went to start it and it did exactly the same thing. Is this vapor lock or a dirty vent in the cap? It only happens the day after a fill up. Any Ideas?

 

[Macguyver]

Venting likely

Venting likely

Sounds like a non-venting cap building up a vacuum in the tank to me. Easy way to find out is to use a clear line down to the carb inlet so you can see if the gas is flowing.

I believe you should be able to dissassemble your cap and clean it, if not, then douse it with brake cleaner, let it sit a minute, and blow it out with compressed air.

Any other ideas guys?

 

[GTGS]

Why would it only happen the day after a fill up? Do you think gas is sloshing up in the vent and plugging it? The timing is what has me baffled. I will try to get it going tonight then clean the cap and see what happens.

 

[mike_of_bbg]

Fill up = less air in tank = less expandable volume.

 

[Dave8338]

Fill up = less air in tank = less expandable volume.

Nicely stated.