Fuel Issue -- Help??

[mysho22]

Hey guys! I'm having an issue with my 96 GS500E, and would love some help trying to solve it.

The Issue:
The bike is sputtering and dying on me, which tells me this is a fuel issue. This is only happening, though, after I've gone about 70+ miles after a full tank. For the first 69 miles of a full tank I have no issue, but right around 70-80 miles my bike will sputter a few times and then die. It's not running out of gas, as I can usually get 150 miles before even thinking about filling up again (and thats before hitting my reserve as well). This has happened so much in the past 3 or 4 weeks since the issue has started that I'm getting used to just pulling in the clutch and coasting off of the highway through an exit and (hopefully) into a gas station. I don't have to fill up right away, usually if I just put the petcock in the "Prime" position (rather than the "On" position it usually stays in), I can get the bike started again after a few minutes and ride it for another 10+ miles.

What I've Tried
Because it's a 20 year old bike, I wanted to rebuild the carbs anyway, so my partner and I did that for both carbs with new o-rings and gaskets and everything. That hasn't helped fix the issue. I also purchased a new petcock assembly (the secondary petcock, not the one on the tank) and put that in the day that I did one of the carbs as well (I didn't realize I needed two carb rebuild kits, so I had to do the two two weeks apart). After a week of riding with both of those done and the issue still not being solved, we thought it may be a tank venting issue and my mechanic friend helped me blow through both the vents and thread a wire through them to make sure nothing was clogging them.

I'm a student, and this is my main transportation, so I'm really hoping to fix this as soon as possible. To quote a friend of mine, "The worst bike you can ride is the one you don't trust." Anyone have this issue before, or have any ideas on how to fix it? I'd appreciate the help here! Thanks

[gregjet]

It is probably something else BUT from the sound of the fault it MIGHT be a faulty coil overheating. Had the same issue on a Ducati once. Too me ages to figure it as as soon as it cooled it was fine again. Had a break in the coil wire and once it heated the matrix would expand and the wire would come apart. As soon as it cooled it would conduct again.
Same can happen with the reluctor pick up coils.
New set of second hand coils may be worth a try. And test the reluctor coil resistance.
More likely to be fuel but keep it in the back of your mind caus the symptoms fit.

[mysho22]

I'll keep that in mind! I talked to some friends who think it might be the petcock attached to the tank, so I'm gonna see if I can work on that today with the help of my more mechanically inclined friends. If that doesn't work, though, I'll check that out!

[mysho22]

Update:
Worked on the bike yesterday, and it seems like it's just hitting the reserve 70-80 miles into a full tank. Which is strange especially as I usually get 150 miles before even thinking about my reserve. I'm tracking my gas use this week to see if I'm just burning too much gas and it's a fuel consumption issue, or if the main isn't letting gas in after a certain point and forcing me to turn on my reserve too early.

[gregjet]

The filter mash on the tank pick up could be clogged.

[qcbaker]

Maybe the main fuel line is swollen internally or kinked somewhere. If so, that means the carb bowls would fill up much more slowly than normal. So, it would be possible that while riding, you use up the fuel in the bowls (plus whatever small amount of fuel is able to get through the swollen/kinked line) and then you start getting starved for fuel.