Here is a rundown of all the things I have done to the bike to remove hesitation, fix wide open throttle power loss, improve throttle response, no fuel starvation and so on and so on. Thanks to everyone here & the wiki too!

- Adjusted valve clearance to be in spec (see wiki)

- Balanced carburettors with proper tool. The ball bearing method + by ear tuning was close but not quite there.

- Replaced air filter with the proper part. The correct filter has a metal tube inside that limits airflow. If you have incorrect resistance at the airbox side of the carbs, the needle does not react correctly to throttle position. It can lead to sudden rich and lean conditions and general bad experience.

- Replaced the diaphragms and all the seals in carbs

- Returned to stock jetting and needle position

- Replaced the intake boots to remove vacuum leaks

- Replaced carburettor slide tunnels (?). This part was found in stock at www.mikuni-topham.de, the official Mikuni representative in Europe. The price per slide tunnel was 27€ and the part number is N198037. It's strange that these parts are not usually listed anywhere. This is the grey part where the slide moves up and down. It's designed to wear as the vacuum pulls the slide towards the engine. It even has wear indicators! I noticed grey dust in the carburettors and that led me to discover the parts. If it wears out, the slide does not move freely and it can cause the needle and jet to wear out too and become misshapen.

- Replaced main jet and related parts and the needle

- Returned mixture screw to stock position as per service manual

- Adjusted the floats to ensure that fuel level in carbs is in spec. Fuel level affects mixture.

- Serviced the fuel cap to ensure air flow into tank

- Cleaned and serviced the frame petcock. Drilled vacuum holes in fuel petcock to a bit larger size to increase vacuum strength. Replaced petcock seals. This finally fixed fuel starvation at highway speeds. No need to ride with petcock in PRIME position anymore.

- Replaced all fuel and vacuum lines

- Replaced throttle cable and adjusted slack to be in spec

After all this, the bike starts effortlessly when cold or hot. Choke is used for about 10-20mins of riding to ensure idling. The bike idles beautifully when warm. Throttle response is fast and consistent. The revs don't "hang" when letting go of throttle. Wide open throttle leads to increased speed instead of hesitation. While the area around 5000-6000 rpm is a bit lacking in power, it no longer feels like there is hesitation or that the bike is faulty. The bike can be ridden at 120km/h for extended periods of time without fuel starvation issues, with petcock at "ON" position.

The most important trick I learned from here and the forums, that can't be stressed enough is: RETURN TO STOCK - make the bike as it was from the factory and it will work.

Again, thanks for help everyone and best of luck to all newjoiners! I hope this post helps someone.

Good advice, glad youve got it rocking!!!

Great advice, and thanks for the slide tunnel part number. What year is your GS500/carburators? There are 3 versions of the carbs.

Return to stock is my go to method for getting non-running carb bikes back on the road.

We have to remember that all the advice floating around the internet about GS500 carb tuning is from when these bikes were fresh off the showroom floor. When everything in the bike is old and likely out of spec, factory settings are your friend.