First off, thank you to everyone who's posted something on this forum. I've pretty much checked it every single day of the last 6 months while I've been working on the bike. Sure, it's small but it's a ton of fun to ride. I've only ridden it a handful of times, but I'm already in love with it.

Now to the issue at hand... She fires right up. Runs perfect and smooth up until 60mph, and then I start having what I think are vapor lock issues. It'll start to lose power and then it'll die completely. Not the most fun on the highway, but it's at least been predictable, so I'm able to pull over without any issues. Now when this 1st started to happen, I had just finished putting the bike back together, and I had no clue what it was. The bike had been siting for 10 years, so I thought perhaps I needed to do a more thorough cleaning of the carb. Did that, and I had the same issue. I ordered a jet kit Lancer(awesome guy), and fitted it with a 55/155. It ran even better than before, but still the vapor lock issue. I then turned to the gas cap. (I've already replaced the fuel line, and I already have the raptor petcock installed.) The cap was filthy on the inside. I soaked it for a few hours and cleaned it. This freed up movement of the little ball that is inside the cap. I thought that would do the trick. It did improve, but I'm still having the same issue. Now I can feel it try to fight before it stalls, that didn't happen before cleaning the cap. I did notice that the rubber gasket on the cap is cracked in a few places. One way I tested the theory is taking the cap of as soon as I stop. Sure enough, it fired up every time, as if nothing were wrong at all. I take off and accelerate hard up to 60mph, and it would happen again. If I'm cruising up to 45mph, I don't have any issues at all, except a sore face from smiling too hard.

The bottom line question is, is it safe to assume that it is in fact the gas cap at this point? If so, is there anyone that a cap that they know is in good working condition and is will to expedite shipping to me?

Info on bike mods:
1996 2,500 original miles!
Custom cone intake tube, with K&N style cone. Will be replacing with an actual K&N soon.
Custom exhaust with baffle insert.
55/155 jets in carb, and I believe it external adjuster screw is at about 1.5 turns out.

I live in Atlanta, so according to the interwebs I'm about 800ft about sea level.

Any advice is appreciated! I'm ready to take this thing out for some long rides! I'll post more pics and the like when she's completed. I just want to get this issue resolved before I focus on anything else.

authentic yamaha raptor petcock?
5/16 fuel line?
no add on filter?

1/4 fuel doesn't clear air in the line well.
fuel filter with air in can vapor lock.

With cracks in the gas cap gasket ,and after restarting and running up to 60 and have the tank vapor lock that fast ,seems to me very doubtful ,(if you don't hear a whoosh of air enter the tank when you release the cap after it stalls the tank isn't vapor locked.) IF the petcock is a true Yamaha part then that shouldn't be the problem either. It may be that your float bowl level is set to low ,did you check it when reassembling the carb after cleaning? Did you check the condition of the float valve and seat and O-ring ,did you check/clean the filter screen above the float valve seat?

You need to be careful with the pin ,it only slides out in one direction ,due to the carb body being soft metal you should try pushing it out, not driving it out!  then you can unscrew the plate and remove the valve seat ,the filter screen will be just above it. You need only a ruler to set the float level.

If you make sure there is no fuel in the carb, you could try heat (no not a torch!) in the form of a soldering  iron ,placed on the pin briefly, or penetrating oil -(carb cleaner will not attack rust or corrosion as well)

Antmanbee, But that is a static reading, you'll need to start the bike in neutral and run at about 4000rpm(=to 60mph) to see if the fuel level drops due to a plugged screen. The bike pictured has no muffler and the jets are rather large, it may be going to wide open throttle is flooding the motor and making it die because the fuel mix is way to rich.

Maine 413, Your new to the bike ,nothing to be embarrassed about!

So I think I finally solved the issue! The screen was filthy. Haven't had any issues today. I'll take it out on the high way soon. Here's a before of the screen.