1981 gs650g starving at 5-6000rpm

[wardy]

while riding, can't seem to rev past 6000rpm. acts like shes starving for fuel. on centre stand, does the same, but i can seem to rev through the flat spot after a few seconds. once i'm over 6000rpm she revs freely. any ideas??? petcock only work in 'prime'. could this affect it???

[SqDancerLynn1]

The petcock could cause problems. ON the centerstand in netural tho it should rev to redline REAL quick. DO you have the airbox installed???? ITS mandatory for it to run properly!!!!

[wardy]

no, bike has pod filters. well spotted! could that be the problem??? just bought the bike not running.

[duaneage]

Check timing advance weights to make sure they are free and can move. use a timing light to see if the timing advances after 3700 rpm.

[houldsworth1]

I'm with the person talking about the airbox. I had a GS650 with a very similar sounding problem - as soon as I put the top of the airbox on (it arrived with it off) the problem dissapeared.

Good luck!

Barry

[duaneage]

If you need an airbox I have several complete boxes. PM me if interested

[wardy]

many thanks to everyone. firstly, a spring of the timing advance had snapped off, and secondly, after installing an airbox, all is well! thanks again and merry xmas! wardy.

[duaneage]

No Timing advance fools many. A lot of carbs have been dipped and redipped due to advance weight problems.

[IanFrancisco]

Since you say the petcock only works on prime I would suspect a faulty petcock diaphragm. I have been battling with mine - tried to seal it with superglue which worked for about a month, then silicone which worked for about 50 miles. Seal it on the vacuum side not the gas side! I got a diaphragm on eBay from a store called siriusconinc. Very nice guys, they offered me a refund on the part since they didn't have what I needed. I haven't sent it back yet so if someone wants it - $15 shipped.

Item number: 4595914292 - A kit for the GS850G, might fit yours.

The diaphragm in this kit is approx. 36mm square (their part no. = DIA-0).

Here is just the diaphragm for under $15. Item number: 4595914633

The one on my bike is approx. 46mm square and I can't seem to find one. Now looking for an entire replacement petcock. Aggravating that a "convenience" item such as a vacuum actuated petcock could be so mission-critical and a single point of failure that can leave you stuck at the side of the road (don't ask). My symptoms were initially rich running on the left cyl. (sooty plug). Applying suction to the vacuum line to the petcock resulted in a mouthful of gas (yum). After my attempts to seal up the diaphragm there's no leaking but the petcock won't flow enough fuel to run faster than 45mph. Accelerating hard or running at 50mph for about 1/2 mile results in running out of gas and sitting at the side of the road waiting for the bowls to SLOWLY fill up again. Frustrating since we're getting some nice warm weather her in SoCal. I'll be packing a flat-blade screwdriver for the prime screw on my petcock from now on till I get it replaced. Why Suzuki had to put this screwy petcock on my bike I don't know. Both ON and RES require a working vacuum diaphragm to flow gas - no PRI position. Loosening the screw which is supposedly for draining the tank per the factory manual flows fuel to the carb but causes the petcock to drip while it flows - about as useful as teats on a bull. I am hoping a petcock from a TS250 will fit and eliminate this "convenience" I can do without. On my older bikes turning the gas on and off manually was as automatic as unlocking the bike and putting on a helmet...