Topic: symptoms of a malfunctioning fuel tank vent

[Trav-i]

As the thread title says I'm trying o figure out what the symptoms of a malfunctioning tank vent are.  The reason I ask is this while out riding today I experienced an odd recurring problem which would act like fuel starvation it would start to surge a little then eventually quit.  Then after stopping for about 45 seconds 1 carb would overflow (simple tapping would stop it), then it would fire right back up and run for a while.  The last time it did this I caught it early, I pulled in the clutch reved it a few times, and then went on problem free for the rest of the ride. Although I stopped to checkout a store on the way back and when I went to see how much gas I had, I got a bit hiss of pressure when I loosened the cap. When I got home I pulled number 1 float drain srew to see what was in the bottom and all the fuel came out the overflow almost nothing came out the screw hole.  I turned the tap on to see what the fuel looked like and it all ran out the overflow tube (weird eh?), well i put the screw back, and turned the tap onagain and again it all ran out the overflow.  Then I pulled the fuel tank cap, turned it on again, and no leak I left it on for several minutes and it never leaked.  So I may have trash in the needle valve (what else is new), but will tank pressure cause that same problem too or not?  Still gotta finish riding home, so I'm gonna leave the tank cap loose and see what happens.  Oh, and it is a 78 F3.

[Old Scrambler]

Preasure in the tank was likely from heat while parked.  The next time your tank is almost empty take it off and dump the fuel out into a container from the filler hole.  If you see any flecks or rust, get it cleaned.  It does not pay to touch the carbs until you know the fuel source is clean. Check the search feature of this site for directions (many sources) on cleaning your tank.

Personally, I like to have my old tanks steam-cleaned and lined with Red-Kote.

[Really?]

It will act like it runs out of gas after a short ride.  Popping the gas cap will tell you if it is or not when it stopped running.

I do not think that will cause the overflow.  You either need to adjust the float, clean the junk from the needle and seat, take the seat out to see if you have stuff sitting above it, check the fuel line to see if it is coming apart on the inside and make sure that tank filter is actually working. If all of that does not solve the problem, replace that needle and seat.  Oh, make sure there is no more junk in the fuel system from the tank to the bottom of the bowl.