After about a year of searching, I finally found something I've wanted since I was a kid: an R100GS in decent shape for a not insane amount of money. Have been picking away at the usual little issues on an old bike and I've come across a mystery: There's a two-prong plug on the right side of the engine block (right under the tank and in front of the airbox) with nothing plugged into it. I don't know what it's for so search has been unhelpful. Can anyone tell me what that is, and if there should be something plugged into it? The bike runs well, but is extremely vibey under acceleration. It doesn't start as well as I'd expect: requires precise throttle input to start, then I have to hold the throttle open for 1-2 minutes or it'll stall, regardless of temperature or choke position. I've had the bike run through, the carbs synced and had a bad pushrod replaced. Would welcome any thoughts about the vibes. I know the 100 is a buzzier engine, but when on throttle, my eyes go blurry, so I assume it can get better than that. Thanks, UPDATE: Thanks to everyone who helped solve the mystery (of a partially intact pulse air system). The rough starting and poor running continue. I've added a video on pg 2 in the hope that someone can help diagnose the funky air/vacuum noise which seems to be getting worse, as does the starting and vibration at idle and under power.