Rob wrote at 2009-05-26 01:59:32
I know this is a VERY old post +2 years and the poster has surely fixed the issue...but i thought i'd add to this incase someone else is searching for this answer.
I have a GSX250 which has a very similar setup to the gs450. There should be a vacuum port on the inside of the carby. that is, just between the carby and the intake manifold/engine. On mine its the right side. This hose should connect directly to the petcock just behind the Fuel hose. Vacuum from the hose is used to open the petcock's diaphragm and allow fuel to flow when the petcock is switched to ON or RES. If this is not connected you won't be moving anywhere without using PRI(Prime)
Also... its crucial that the vacuum hose be connected either to the tank or at least blocked...if not you'll be sucking air straight into your right cylinder on the other side of your carby and completely screwing up the mixture. For my bike this resulted in the bike revving far too high.
In short, make sure the vacuum hose is connected to the petcock or blocked otherwise your engine will run far too lean or not at all.
I hope that helps someone :)
gs450 cafe wrote at 2014-04-02 23:20:12
the vaccume for the petcock goes on the left hand carburator forward of the choke lever, underneath the pilot screw adjustment (if adjustments have not yet been made to the pilot/mixture screw, there will be an aluminum plug above and forward of the choke lever)
Technical, engineering mechanical based, also some electrical issues, two stroke and four stroke, various makes and models, off and on road.
Been riding bikes since 12yrs old, to name but a few, villiers starmaker, Cotton frame, Triumph Tiger cub James 150 old stuff. First on road bike 1976 yamaha rd250 coffin tank, then Triumph Bonneville 750, Moto Guzzi 850 california, custom hardtail chop Honda 550 with yoshi 610 conversion. Also off road from 100yz in 1981, cr 250, some comp experience,raced MX bikes, Karts, also Autocrossed cars, and F2 Super stox. So have wide experience. My son now rides MX right now a cr80, Garage is also home to many other projects and good running Bikes. I often buy, restore, Bikes, mainly crossers, and then find them a good home!
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Education/Credentials Higher National Diploma HND in engineering in Design and Manufacture, NVQ in Supervisory management spent many years in the auto industry, and a garage equipment company with outlets in UK and abroad.