Random Questions

[surveywaters]

What is it on the petcock that is going bad if it isn't a bad o-ring for diaphram. The rest is cast. Also, is there really enough pressure from the tank to break the seal at the float valve? Many motorcycles merely have an on/off and I have never had a problem leaving one on in the parking lot.

[surveywaters]

It looks like 2 out of four of my needle valves are not sealing properly, probably some cheap Chinese parts.

[bwringer]

What is it on the petcock that is going bad if it isn't a bad o-ring for diaphram. The rest is cast. Also, is there really enough pressure from the tank to break the seal at the float valve? Many motorcycles merely have an on/off and I have never had a problem leaving one on in the parking lot.

It looks like 2 out of four of my needle valves are not sealing properly, probably some cheap Chinese parts.

Many before you have been down the path of petcock denial...

All the rubber bits inside the petcock can go bad and evidently are bad on your bike. Plus, the cast metal body of the petcock very often corrodes and becomes unusable. The rebuild kits are expensive, shoddy junk, so replacement is the safest option.

I prefer not to take chances with a valve that controls the flow of a highly flammable substance a few inches from the ol' twig-n-berries...



Even if they're in perfect condition (in your case, they may or may not be fine but they are likely dirty with corrosion from the bad petcock and thus not able to close), the float needle valves on a GS are not designed to keep gas in the tank indefinitely. Hence the automatic vacuum petcock. If you changed to a manual petcock, you'd still need to shut it off every time you walked away from the bike.

YMMV, but there have been many reports of GS riders who left their petcocks on "Prime" and returned the following morning to a crankcase full of gas.

Yes, there are some other brands of bikes that use rubber-tipped float needles that seal a bit better in the parking lot, and thus it may be relatively safe to leave a manual petcock on for the day. But on a GS, even a perfectly functioning float and needle valve can and will seep.

[BassCliff]

Hi,

Thanks a bunch. I don't see a hole there,surely that doesn't just stick on, that seems kind of iffy for a quality vintage Jap.

On my bike, and I suspect yours too, that cushion (#7 in the parts fiche picture above) is installed on the bottom of the frame near the left rear passenger foot peg. Hopefully there is proper clearance with your aftermarket exhaust. Most aftermarket 4-n-1 exhausts are on the right side.


Thank you for your indulgence,

BassCliff

[surveywaters]

Thanks for that Bass. I was studying the stand last night and couldn't figure it out. The exhaust on this bike is not too far off of stock. It is a pair of megaphones, much like factory, welded on to the Y's that were part of the stock system.

[surveywaters]

Can someone explain how prime works on this petcock? I opened it up and there was no spring, so I fashioned one, replaced the o-rings and sealed it back up. It works fine with a vacuum and is sealing splendidly but prime want open it. I disassembled and inspected and don't see how it ever would work. Should there be a part between the plastic barrel of the selector and the plunger tip? I see nothing that would manual puch back the plunger and I see no bypass hole.

[tom203]

Maybe someone has been at petcock before you! But believe or not, prime does work on a decent petcock (I tested mine today before heading out in 48 degrees). Stop playing with it and get a genuine Jap made replacement and find other hobbies!

[surveywaters]

I can't do it. I will make this work, or at least understand why it won't; this is how we better ourselves. I have it functioning properly, but there is no flow on prime. I want to understand how switching to prime opens the plunger. I see no mechanical device which would break the seal.

[hoppy1]

I can't do it. I will make this work, or at least understand why it won't; this is how we better ourselves. I have it functioning properly, but there is no flow on prime. I want to understand how switching to prime opens the plunger. I see no mechanical device which would break the seal.

When you move the lever to PRIME, it opens a BYPASS port inside the petcock body so the gas can flow out without any vacuum. I'll bet that port is clogged. Take it apart and make sure all the ports are clean. Good luck, Mark

[surveywaters]

Thanks hoppy, I must have done a poor job looking, I didn't see any ports

[surveywaters]

Nope, no passage, still a mystery how prime works.

[bwringer]

Nope, no passage, still a mystery how prime works.

The passage is in the petcock handle.

There's a rubber whatsit with four holes under the handle.

When you move the handle, a passage in the handle connects two of the holes. Which two holes it connects determines what happens.

[surveywaters]

not on this 1982 GS850gl. The handle turns a plastic bung. This is not the four hole style.

[hoppy1]

not on this 1982 GS850gl. The handle turns a plastic bung. This is not the four hole style.

When you look at the plastic bung,is there anything that looks broken? Also, when you have the petcock apart, when you move the lever does the bung move also? There has to be something not moving correctly in there. Post some pics if you can!!

[surveywaters]

Bung moves smoothly, nothing is broken, the knob turns it nicely. Goes from 'reserve' to 'on' properly, prime just does nothing. It can function with a vacuum in prime. I have looked at this thing for hours, there is no bypass hole, the only way for fuel to get through the plastic bung and out of the brass hose barb is by flowing through the orifice which is regulated by vacuum. There must be some mechanical means by which the diaphram's plunger is pushed back when the unit is put ino prime.