Fuel petcock issue & Bike goes flat beyond 8K RPM

[moeenm]

I'm from Pakistan and I have 2003 GS-500 with a leaking petcock.
(bought used kinda alright taken care of and had to get ringwork done because of bike chugging oil).

For now I've plugged the vacuum and run manually between PRI for ON and RES for OFF.

Parts are not available for this bike over here as it was sold for a very limited time in Pakistan (1996-2003) to Police only and alot of bikes were abused/neglected-state auctioned.

My question is, since Yamaha Virago/V Star new fuel petcock is available here (which is also vacuum operated), May I just buy that new and solve the leakage problem?

My 2nd concern is most likely with stock jetting (I guess).
Bike is kinda sleepish on low RPM till 4.5K, then it wakes up until it reaches 8K RPM and then runs flat. I am getting an average economy of 19KM/ltr which is about 44.7MPG. Do I need jet replacement? For those who have rejetted their carbs, how does it affect the fuel economy?

This is my first bike in above 125cc category and I'm learning alot through this forum.

Thank you!
- Moeen

[Joolstacho]

There's very little power to be had above 8000rpm, you'll over-rev it if you go up there.
Use standard size factory jets, use factory exhaust and air cleaner. They knew best.

[Bluesmudge]

44 mpg sounds average. You won't do much better than that. Maybe 50 if you take it easy. Rejetting will only make it worse.
I agree that sounds correct that it's flat above 9,000 rpm. No more power to make after that, it starts going back down. Also no power down low...it's and old air cooled bike with mid 1970s technology.