Petcock question(s)

[pdqford]

A little background:

Last summer my 1980 GS750ET (which I have owned for the last 27 years ) didn't run very smooth and would tend to stall at idle. I decided that this spring I'd put into practice a number of the good things that I have read about on this GS site. Gonna start with the carb cleaning. Then figured this would also be the time to change the sparkplugs and check the valve lash, since all I have ever done to this machine is change the oil and RIDE it all these years. (And now I see that the barrel to crankcase gasket is weeping so I'm even thinking about changing that - maybe. )

Okay. So all I have done so far is pull the tank. I took the petcock off and flushed out the tank with clean fuel. The tank looks clean inside. (I always have stored the bike over winter with a full tank of fuel.) I decided to take the petcock apart but it doesn't want to come apart and I don't want to get physical with it for fear I might break something or tear a gasket. I applied a vacuum to the petcock vacuum port and I can see the piston retract and I see how the fuel can flow to the carbs.

What I don't understand is, and my question is, how does the prime function work? There is a small slot where you put a screw driver in there and rotate the little plastic thingy, but the owner's manual is not clear on how far or which way you turn it to get the prime to work. When I turned it I expected to see the piston retract so the fuel could flow to the carbs, but when I rotate the plastic thing the piston doesn't move. (BTW, there is no lever on this petcock and I'm sure it is the factory original one.)

How do it work?

[chuckycheese]

Whooooooa!

Well, I can understand why it might run a little rough after 27 years so a little servicing is probably not a bad idea!

If your petcock doesn't leak gas when your tank is off of the bike (with gas in it) and it does flow when you put vacuum to it...I'd carefully set the tank aside and deal a few of the other issues. If you don't have a good service manual, get one before getting started.

I'd start by taking off the carbs, disassembling them and dipping them. All you need to know is here on the website and be sure to replace all of the "O" rings with new ones from Robert Barr. While they're "in the drink" you can adjust your valves, change your fork oil and your brake fluid, lubricate all your cables, check your electrical connections and everything else that's recommended for the "27 year service interval".

Feel free to ask questions while you're preparing for your next 27 years on the road and you'll get lots of helpful advice!

If you want to learn more about the infamous "'80 petcock", a search here on the forum will tell you all you need to know.

[BassCliff]

Search feature:

http://www.thegsresources.com/_forum/showthread.php?t=139099&highlight=1980+petcock

Thank you for your indulgence,

BassCliff

[pdqford]

Follow up question

Thanks guys. (I had done a search for petcock and was overwelmed - now I know I shoulda added "1980" to the search criteria since there is something specific to the 1980 model year.)

Over the last few months I have downloaded the CV carb pdf from John Bloemer (?). Picked up a gallon of Berryman's. Also acquired a set of carb o-rings from Mr. Barr. And downloaded a nice shop manual on the GS750 16-valve model (Thank You, Basscliff) to assist me in setting the valves. I'm sure I'll have more questions as I get into these projects.

But as a follow up, when I removed the fuel tank there was a hose connected to the fuel gauge assembly that went down below the transmission. Is this some kind of a vent for the fuel tank? (I did see what looked like a breather vent under the gas cap so I was wondering what purpose this hose serves. )

[Billy Ricks]

It's an overflow in case the tank leaks from the plate the float mounts to.

[pdqford]

Got it! Thanks Billy.