Dude, where's my gas?

[nutz4spd]

Last weekend I finally had a chance to mess with my GS750 some. When I parked it a few months back it had just about a full tank of gas. When I removed the tank I noticed it was fairly light. I set it aside and when i pulled the air box off if was almost full of gas!! Great, 1/2 tank wasted... The petcock, I don't think, is original. It has positions for Reserve, Run, and Prime. I leave it in the run position since it's vacuum operated so it shouldn't leak right?? Not unless the diaphragm has gone bad. I could pull the line off and turn it to Prime and gas would run out. Move it back to Run and the flow stops. I noticed after I filled the bike up it wasn't running well. I could get it started, but it wouldn't idle worth beans, especially once it started warming up. I rebuilt the carbs back in January and it ran ok afterwards. Ran it low on gas and it started popping and stalling so I filled it up. Hasn't run right since. Now half of the gas has managed to drain into the air box while it's sat. Anyone have some tips or suggestions on what to look for/at?

[yank]

Check and see if your oil smells like gas and is over full. do not run the bike until the issue is solved. I would suspect it is a carb problem, needle valve. Someone else will chime in.

[rphillips]

Yep, been there done that 2 times. Bet'cha oil is over full. If it is you have both a petcock & a needle & seat problem. If the petcock works properly, it will stop the fuel flow. If all needles & seats are working properly, they will stop the fuel flow.

[steve murdoch]

Could be when you ran it low it picked up some crud from the bottom of the tank and it has made its way into the carbs.
The tiniest piece of rust/sediment can plug a needle valve.

[Steve]

I leave it in the run position since it's vacuum operated so it shouldn't leak right?? Not unless the diaphragm has gone bad.

Leaving it in RUN or REServe is the proper way to store it. The diaphragm has nothing to do with whether it leaks or not, it only 'pulls the plug' to allow fuel flow. There is a spring that pushes it back into place and an o-ring that actually seals it.

Could be when you ran it low it picked up some crud from the bottom of the tank and it has made its way into the carbs.

IF, it picked up any crud, it would have to make its way past two filters, so yu might want to check them. Actually, there are FIVE filters. One in the bottom of the tank at the petcock, then one on the inlet for each carb.

I would put my money on a dirty sealing area inside the petcock, and the o-ring can't quite make a proper seal.

.

[nutz4spd]

After cleaning up the mess I pulled the petcock off and disassembled it. There wasn't any trash in the petcock but there was a little bit around the outside of the screen. I was also surprised at just how weak feeling the spring was that is supposed to push the diaphragm in. Since it was weeping anyhow I'm just going to replace it with an OE one. I pulled the carbs back off and removed the bowls. Two of the needle screens had some trash in them so I cleaned them out. Didn't see any other trash but I think I'm going to blow a little air through the carbs to maybe clear out anything else that might be logged in them. Would adding an inline filter for say, a small engine, be of any benefit? I wouldn't think it would hurt anything but what do I know...

[Grimly]

<.... and cue the anti-filter mob>

Anyway, my position is always fit a filter. Be wary of many of the so-called bike filters punted out on ebay or Amazon, as they're a bit restrictive and frankly, look shoddy. Basically, fit as big a one as you can and from a reputable supplier. Some recommend lawn tractor filters.

Even before I ditched the carbs and ran a big single, I had a filter. Since ditching the carbs I've got scads of room to fit a decently-sized one that I can see at a glance whether it's getting dirty or not.
I have filters on my other bikes, too.
I can tell you what's a real bugger - the stupid little filters in the intake of each carb that get clogged up easily by crap that comes through the mesh of the in-tank pickup filter. That kind of thing leaves you stranded at the side of the road with no easy remedy, because removing the carbs and cleaning those little filters is a total pain in the head. That can be avoided by having a decent in-line filter.

[nutz4spd]

UPDATE: I swapped out the petcock for an OEM one. Replaced the plugs. Cleaned out the carbs. I went to change the oil and I drained about 12 quarts of gas/oil out. I'm currently letting it sit over night with the filter and drain plug out to vent the crankcase. Now I'm concerned. As I've never experienced this, what do I need to do after this? Can I just fill it back up with fresh oil and run it as is or is there something else I should/need to do?

[chuck hahn]

Just refill with new oil and a filter....

[rphillips]

What about the float needles, if they are working properly, the gas should not get past them, even if petcock fails. Should it??

[chuck hahn]

Big misconception. Float needle function is to REGULATE fuel flow as needed when running. They are not a point of positive shut off. And if they are CV carbs fuel can leak past the orings on the seats as well.

[chuck hahn]

I should also note the little tip thats spring loaded on the needles can go bad or stick making a needle leak all that much more.

[nutz4spd]

Everything in the carbs are brand new. Is there a way to check the needles while they are still in the carbs? What would you look for besides obvious damage or deformity?

[chuck hahn]

Not really a good way to inspect other than take off the bike. Look for free movement of the needles when you move floats u and down. Are the spring loaded deals springing. Take out the seat retainers and VERY GENTLY see if the seats feel good and snug. I use regular pliers and i super glue rubber pads on the jaws to prevent damage and supply some gripage. NOTE.. dont squeeze hard..just enough to grip and see if they feel like the orings are snug. Too much squeeze can make the seats oblonged and then theyre juned. A simple little twist will let you know. Idea is to eliminate fuel could be seeping past orings.

Put bowls on and turn the rack upside down and back upright kinda quicky. youre listening for each float to kinda make a thunking sound meaning they are most likely moving good past the bowl gaskets..yes i have had gaskets squish out and drag against floats...

Petcock... get two water bottles some electrical tape and some lines for the fuel line and the vacuum line. Hook up a line to each nipple and put a line into each water bottle and tape the bottle to the line. Petcock in ON position. Let it set at least overnight then check bottles for fuel. Whatever bottle has fuel in it tells you if the diaphram or lever side has failed. Ideally you dont want fuel in either one.

[OldVet66]

I had a similar thing happen this winter, gas leaking out of one of my carburetors. I have finally gotten around to fixing it. I have a set of new needles and seats that will go in the carburetors and I am totally done with Suzuki petcocks. Fortunately Z1 Enterprises is selling Pingel petcocks and adapter plates (depending on the year of your bike). I got the 6211-AH (fits all GS 750-1100 and 1150 unless you need a dual feed) petcock $100.95 and the plate that matches my '80 tank bolt spread of 50mm A1902-C $35.95. The other plate is 44mm A1702-C. No more petcock problems for the life of this bike. I understand the safety theory of the vacuum petcock but a Suzuki of this era will leak gas if it is on it's side through the gas cap (the top seal will not hold the pressure of the gas weight) so what is the difference besides training yourself to turn the gas off manually before you get off the bike.