That's a Texas GS450T, y'all

[GSXR7ED]

Well that's the interesting thing; There's no sign that it is leaking that I can find (which ultimately I still don't know where the gas is coming from - Everyone online tends to point to rebuilding the engine which sounds costly and painful so trying to pin down the problem) I disconnect it from the carb and it appears to run as normal; Fuel/Reserve will not release gas while disconnected from the carb (CV/Vacuum Carb) and Prime does let gas continuously flow, but I tend to not leave it on prime; I was more wondering if this could be a result of something else, or if it is a matter of my petcock how do I test that? Or if I did leave it on prime, will that happen if I forget it over night or something similar?

I'm a newb, so 100% I'll take any advice; it just sounds off since I know it's flowing / cutting off without the carb, and that's after trying 3 different petcocks using the one with the best results.

You won't see the gas leak because it's internal to the petcock...turn it to the off/RES position when you are parking your bike...turn it on when preparing to ride.

If you continue to have fuel in your oil when the petcock is turned off/RES, you probably need to replace it.

The only time you would put petcock on prime is when you're about to ride and had it turned off.

Once started, put it back to the "ON" position.

 

[Rich82GS750TZ]

Did I miss something? What GS petcock has an Off position? ON, RES, or PRIme, AFAIK. Or is this an aftermarket (Pingel?) with an actual OFF position?

 

[Zellock]

Sorry, let me clarify since I have done more research, long since that mistake occurred of leaving prime on as long as I had; My petcock is a standard Vacuum / CV Petcock for this year model (1981 GS450T - It is an OEM Petcock) - It has 3 positions;
-Fuel/On (Middle): The CV Petcock allows for the gas to be pulled from the top most filter - Allowing approximately 3/4s of the tank to be pulled into the petcock and be used before it cuts off
-Reserve (Forward): The CV Petcock allows for the gas to be pulled from the bottom most filter - Allowing FULL use of the gas tank; acting as an 80's "gas meter" and knowing when the sputter kicks in, time to hit the gas station.
-Prime; The Petcock says "WHO NEEDS CV?!" and just dumps gas into the petcock without any vacuum being applied.

I have, since learning that, tested the 3 petcocks I had. One did not let gas out at all - That's now on the wall of shame. One let gas out on all 3 positions; also on the wall of shame.

The third petcock did what it was supposed to; no gas is pulled through in Fuel/Reserve unless the bike is running (though it does feel sluggish when checking the fuel filter), and dumps gas on prime (again observable with the gas line removed from the carbs, or through the clear fuel filter).

These days; the gas stays on Fuel/On, unless I've done carb work - then I'll run prime long enough for the gas filter to fill, then turn it right back to fuel (per the instructions of the previous owner - dad.)

(Pictured - Similar to mine in design)

 

[Rich82GS750TZ]

You mention a fuel filter in the fuel line between the petcock and the carbs. There are some varying opinions on this, but if your new gas tank is as clean as you say, you don’t need the filter. Your bike didn’t come with one. Try running a straight fuel line with no filter. They have been known to cause problems.