Dear "Brothers in Suffering",
if I wouldn't hav'd anyway, let's say a lack of hair on my top, I would have lost them over this issue.
But now business:
My all in all reliable GD/Vista 150 showed a sudden unpredictable temper im form of surging at idle, not downrevving to idle anymore, lazyness in firing up and so on .....
Changed sparkplug, did valves, all those nine yards (pulling carb, cleaning with ultrasound, changing o-rings, etc.) with carb adjusting, to no success.
Then of course I suspected my pilot screw, because no change at all when turned in or out.
Also electric bystarter was checked and did not drive out when connected to a battery
Hmhh, this small tubus clogged.
After reading a lot in this forum and in others, mostly there is no success if this bybass is closed.
Except to drill the copper plugs off and....
A bystarter alone original is €107,- plus an original carb for about €250,- NO WAY Ruffus, you are frugal.
Okay, a replacement has to come.
Found at Amaxon in form of a nearly original new KEI*HIN CVT 26 carb with bystarter for €41,99, overnight delivery.
Looked good, but a little bit shorter than the original, without heating element and with jets way too big for a 150ccm.
Well since there was a nice set of jets in my storage, "let's go", I thought.....because
the main jet-stock has a 4mm thread in this substitute. So you would need jets with a 4mm thread. But my stock was 5 mm.
No problem, a 5mm thread tapped in and, I thought in my juvenile innocence, the bigger the better, main jet 115/ idle 40.
Done, testdrive, problem still there. Idle not adjustable, high revving, dies upon adjusting, sparkplug sooty.
Hmmh, ..after a few tries I had finally a light moment and put minimum configuration of main jet 105/ idle 35 in it and all probs were history.
Have to say with CVK carb, better acceleration, appr 8km/h more topspeed.
Thank you to @dan.v for this thread below which helped alot.
https://www.kymcoforum.com/index.php?topic=27340.0