1985 Vf700f potential vacuum in gas tank.

This summer I purchased a 1985 vf700f CA and for the most part it has run very well. The only issue I've run into is that occasionally after letting it warm up, I will pull out of the driveway and half a mile down the road it will die out like it runs out of gas. I found that in order to fix it, I need to shake the bike and swash around the gas in the tank. After that, it will start right up and run perfectly. Is this an issue with the petcock closing itself and pulling a vacuum, or something else entirely?

 

Try opening cap and see if there is a vacuum from gas being sucked out. I believe vent for air to replace gas is in the cap, check the seals. You can not replace rubber seal on 83-85 gas caps, be careful with rubber.

Check the fuel line and connections for air leaks, check inline fuel filter for debris (on left side of bike, behind regulator plate)

Petcock is a manual valve that has a blocking plate that rotates over the holes to pipes that feed carbs. Try turning to reserve, if problem persists (both feeds share the tank, so vacuum would be common to both) then there is a problem with venting.