I've recently wrenched on a GT200 for a friend, which was built from an assortment of damaged and/or incomplete GT200s. It's running well enough, but I'm still a bit bothered by the performance of it.
When I rebuilt the Keihin carburetor, I noticed the foam "filter" that fits into the right side of the carburetor (as-installed in the scooter) was pretty desiccated. A second carburetor had the cap, but no foam at all. When we put the bike together, I re-used the foam.
The bike was very boggy and lethargic. I suspected it was because the foam "filter" was pretty worn and that the bike was losing too much vacuum on the diaphragm and not lifting the throttle piston sufficiently. I made a replacement insert out of a new-spare moped filter that was a bit more open-cell than the original filter foam, but used a larger piece in order compress it a bit it increase the filter density. It seems to work, though the bike still seems a touch boggy when revving up.
Is there a recommended part for this? Keihin doesn't mention it anywhere and to be honest, this is the first CV carb I've come across where it deals with air that isn't in a vacuum line or manifold. I've even looked at OKO carbs for this and struck out thus far.
Any guidance is appreciated.