On the 800cc buggy this valve connects to the valve cover breather filter on the intake manifold. At idle it vacuums air from the valve cover and at higher rpm when the turbo kicks in it closes off to stop pressure from entering the valve cover. Mine vibrates alot at idle and when closed off the engine acctually runs smoother and idles much lower.

Does anybody know if necessary this valve is?

It looks like a PCV valve. If you are running a stand alone crank case breather you dont need it. PCV ( positive cank case ventilater) It is designed to suck blow-by out of the engine, With a breather tube and a filter running from your valve cover that would be fine. Just be sure to put the breather filter up high enough, sometimes with a turbo at boost it will blow oil out of the filter. I have found about 12'' above the valve cover is good

How about the PCV valve? Do I just plug it. And why does the rpm drop so much when I plug it? This is the tube from the pcv, plug it also?

Yes that is the one. The idle climbing is because when it closes it shuts down a vacuum leak, you may want to run the car hard and check the plugs, may need to rejet the primary.
As far as the PCV port just plug it, They stoped useing it on the newer carb modles GK-32 I use a EGT gauge to monitor how rich or lean i run, as well as all of the cars i install turbos or supperchargers on.

Thanks

hmmm I didnt know that was a valve, I thought it was just a open port that always sucked crankcase fumes at all rpms.
To me it seems like the pcv makes the middle cylinder run lean in comparison to the outer two cylinders because the valve is mounted on the middle runner so the extra PCV air is only going in one cylinder. it really should have been farther up the manifold by the carb...

I just put a vaccum cap on the port and the nipple on the valve cover and then a little breather filter on top like you already have. when I go to boost Im just going to plug up the valve with JB weld or something.

You should notice a difference at idle. and yes if will lean out #2 cyl at idle only, under boost it will close the valve. Pluging the hole will be fine.

Took apart the PCV valve and noticed the spring is broken in two. Leaving the bearing floating in the middle which explains the vacuum leak. But like you said only at Idle. Closed everything up and now starts and idles from the get go. Planning on running this weekend after installing new front spindle bearings on both sides. Good thing for the bearing shop around the corner.

NIIIIIICE, have fun and let me know how things work out

Had to replace the PCV valve, the buggy would not power the turbo at all. I think is was running to rich but not really sure. After fixing it, it ran great. This is at the races at Pismo. And steep dunes after a long night of wind. 6 year old loves it 16 year old doesn't.