GSX400e petcock with strange screw.

[Guest]

Does anyone know what the purpose of this screw is?

[dorkburger]

I think I read recently that it's for priming the carbs.

[Rich82GS750TZ]

I believe with that type of petcock, that screw is used to prime the carbs. Most GS petcocks have a 3 positions: res, on, prime. Yours is like the one discussed here:

https://www.thegsresources.com/_forum/showthread.php?246384-450s-petcock-screw&highlight=Petcock+screw

[Polish-Jack]

So how does it work exactly? If I turn it a couple of times will it let fuel flow without the need for vacuum? Can I remove it completely to drain a tank?

[Rich82GS750TZ]

That I do not know. Sorry

[hugo151]

Yes ,it's the prime screw, same as on a gsx 250, the rubber o rings can perish, & then let fuel to constantly run, causing hydro lock. You just unscrew it a couple of turns to prime carbs if you need to. thanks

[Gorminrider]

Polishjack, where did you get that? and/or is there a number on it?

(again,yes it is the prime ...handy to fill carbs or drain tank or run the bike if the vacuum mechanism fails-but that one looks new! )

[John Park]

Solves the problem of leaving it on Prime by mistake. It can be easy to confuse Reserve and Prime, and when the fuel gets low, either way has the same result - well, until you park the bike and don't get around to filling it for a week. Given that the design required a brass stepped plunger and two o rings plus machining a seat and threading the.......well, the accountant liked the three way version better.