1981 GS650 Problems (new forum member)

[Guest]

Hello all I am new to the forum so hopefully I am posting in the right place. I just bought a 1981 GS650 about a month ago with 35k. The bike looks like it was taken well care of, but there is something wrong with the bike I can't seem to figure out. The bike starts up fine but doesn't idle very well. When you ride it there is a loud knocking noise that seems to come from the left side of the motor during mid range rpms. When I first pulled the plugs, cylinder 1, 3 and 4 are burning kind of whiteish while cylinder 2 plug is jet black but not wet. I did a compression test and all cylinders are between 115 and 125. I than bought 4 new carb rebuild kits and completly cleaned and replaced parts in carb. Still no luck. Runs the exact same weak idle and knocking noise. Than I replaced both coils because they were the original an I am getting good spark on all 4 as they were with old coils. Still runs the exact same.plugs are still same color 3 whiteish and 1 black. What could be the issue? I don't know where to start next. Any help would be appreciated

[tom203]

Carb rebuild kits often contain inferior parts, so please find your old parts asap. These carbs are real fussy to clean properly- this is likely your problem.
Number 1 cylinder is under the clutch hand lever, right?? Number 2 black plug could be petcock problem- fuel dribbles down that vacuum line connection.

the loud knocking noise is bad news, but maybe it's due to #2 cylinder getting washed out by gasoline- let's hope so!

for general info, go here

http://members.dslextreme.com/users/bikecliff/images/GSR_Greeting.html

for proper carb cleaning delve deeper

http://www.mtsac.edu/%7Ecliff/storage/gs/Mikuni_BS-CV_Carburetor_Rebuild_Tutorial.pdf

oh yeah, Welcome

[tkent02]

What he said, it's the petcock.

[jwebb]

Yes correct number 1 cylinder under clutch, 2 under petcock. I connected a clear hose to the vaccumn line that goes from gas tank to cylinder 2. I sucked on it and fuel came out so I think your right that the petcock diaphram is shot. This is the test I read online to do. Is that the proper way?

[tom203]

Yes, if you suck on vacuum line and fuel starts flowing in it , your petcock has failed! Your oil is likely contaminated with gas, so change it when you get new petcock. Try Z1 or this florida guy where I got mine

http://www.georgefixs.com/brand-new-suzuki-gs300-gs450-gs550-gs650-gs750-gs850-gs1000-gs1100-petcock/

[jwebb]

Thanks Tom203. Just ordered the petcock and will let you know how it runs after i install it. I will take your advice and change the oil immediately as well

[60ratrod]

the white plugs means you're running lean on the other 3. once you get the new petcock and do an oil change, you need to adjust the ide/air mixtures, and do a vacuum sync.

[nicolettijd]

Hello from a fellow newbie.

My petcock is also bad but it's stuck in the always flowing position, and so far isn't clogging my #2 cylinder. I put in an additional on/off switch in the fuel line (7$ for a new switch as opposed to $60 for a new petcock) - Actually I'm interested in hearing opinions about this - any reason why what I did might not work permanently?

One thought comes to mind - you'll also want to do a valve adjustment if you just bought the bike and are having some fuel/air issues. It definitely helped me out when I just started trying to figure out what was going on. Mine ran better, but it wasn't my main problem.

valve adjustment

http://members.dslextreme.com/users/bikecliff/images/16valve_adjustment.pdf

Besides that there's a bunch of great tutorials on Youtube by this mrmaxstorey guy:

like this suzuki carb rebuild was perfect for my GS1100EZ:

https://www.youtube.com/watch?v=dD3UWtLfzX4&index=15&list=PL0557182BD945AE00

I think your carb is very similar, but check to see, because I'm not certain all this info applies to your model.

[tom203]

The nice thing about a functioning vacuum petcock is that it's good insurance against worn out fuel needle seats. With engine not running petcock is blocking flow to carbs. You don't have to remind yourself to switch it off- it does it for you. Sooner or later, you might get distacted and fail to turn your shut off valve off. On dirt bikes, you'll just get a gas puddle under bike, but with these CV carbs overflowing fuel will find its way to crankcase- you might not notice right away.

[jwebb]

So I installed the new petcock and changed the oil. Bike is running way better. Down the highway it runs great, but still having some idling issues. How do I do the ide/air mixtures and vacuum sync that you reccomend?

[tom203]

image.jpg

So I installed the new petcock and changed the oil. Bike is running way better. Down the highway it runs great, but still having some idling issues. How do I do the ide/air mixtures and vacuum sync that you reccomend?

Run down the highway a bit more before idle worries - this thing might have sat for a while waiting for you. First thing you should check are valve clearances, despite any previous owner's claims - you need this done before carb adjustment and sync. If your hot idle is too low, turn the idle stop screw a bit to keep from stalling.You can reach in and turn knurled knob between carbs to change it-see pic