Jittery Vacuum Piston

[Jhonesy]

Hi everyone.

First time posting here, sorry if this is the wrong place for this.

Bought my GS500 a few months ago. Thought I was getting a hot deal, since it only had 2100km and it was from the year 2000. Trusted the seller and now it has come to bite me in the ass.
Bike started to have power delivery problems a month after buying it. Compression is good, so are the electronics. When I took the filter out and peeked the carbs saw that the right carb vacuum piston was jumping up and down non stop. The vacuum chamber above the carb is also a little bit dirty, the left was was clean.
I'm guessing its a vacuum leak somewhere but can anyone pinpoint me where the leak might be?

EDIT: Just asking for some advice before I fire up the parts cannon. It would be nice if I could buy just one or two things instead of a full carb rebuild kit. Apreciate any help you guys can give.

Link to video: https://youtu.be/5MzeCy-A4VM

[Armandorf]

If you want to fire up the parts cannon, buy it all, but is a used bike after all, and although you can solve now your problem a new one will arise in the future.

You have to at least clean jets and inspect diaphragms, check valve clearenace and compression(which you did).
Oil consumption is ok? How was the compression?
How are the spark plugs, when removing carbs you can see if some intake valve is noticeable dirty or oily.

spray something flammable like wd40 or starting fluid, to look for air leaks

[Jhonesy]

If you want to fire up the parts cannon, buy it all, but is a used bike after all, and although you can solve now your problem a new one will arise in the future.

You have to at least clean jets and inspect diaphragms, check valve clearenace and compression(which you did).
Oil consumption is ok? How was the compression?
How are the spark plugs, when removing carbs you can see if some intake valve is noticeable dirty or oily.

spray something flammable like wd40 or starting fluid, to look for air leaks

Compression was 150 PSI on both cylinders. The diaphragms were good but the right one was a bit dirty. No oil consumption. Left plug was white (but I imagine that was because of a too lean mixture due to a vacuum hose being disconnected, that has been fixed) while the right plug was covered in gasoline and black, no oil residue, though.

I did try the WD-40 method and it worked a bit too well. The bike jumped to 4000/5000 rpm and filled my garage with white smoke but I couldn't tell where the leak was, gonna have to try that again.

I did notice later that the exhaust is looking blacker than it should, slightly, and only while idling.

[Armandorf]

dirty in which side?
check mixture screws and pilot jets if its behaving errratically at idle

[Jhonesy]

dirty in which side?
check mixture screws and pilot jets if its behaving errratically at idle

The one in the right carburator (the jittery one), vacuum side.

[Armandorf]

you have pair system hoses? you can plug them form the white caps

[Jhonesy]

you have pair system hoses? you can plug them form the white caps

I don't know what "pair system hoses" menas and I don't think there are any white caps on the carburators, not that I've seen, at least.

[Armandorf]

in 2000 modeli think its a regular carb with black plastic diaphragms cap, spray very carefully wd40 to find the leak, check carb boots to carb and to cylinder head

[Jhonesy]

I fixed some of the issues mentioned above. The jittery piston is actually the one that was correct, I fixed the other one by properly connecting vacuum hoses the mechanic left unconnected.

I have another question, how do I remove the main jet holder (the long one with small holes on its side) and the vacuum piston guides (the plastic ones)? Do I just pull them from above?

[Armandorf]

needle holder on newer carbs is a friction fit between 3 tabs with an oring it  comes oput with needle pliers staright and firm, you can rotatee to maybe unstick it, i broke one and had to change the slidew, can t understand you  doubt

[Jhonesy]

Thank you for the help. Rebuilt the carbs with the Keyster KS-0673NR kit. Just ned to get a pair of intake boots and then install and tune everything.