Fuel Petcock and Fuel Gauge Questions

**Anonymous** · 11-22-2002, 09:23 PM

usually you have a vacume operated petcock--there are 2 hoses going toit--one is from one of the carbeurators which supplies the vacume to open it an instant after the engine starts--leave it in the on position--the prime is in the event the bike has been sitting for days and tyhe bowls need to be filled before starting. If you use your bike daily as i do it shouldnt be necessary
even after a few days. the reserve is just what it says. If your guage is not working. The forst thing I would look for is to see if the wires to the guage a re disconnected. Whenever the tank is removed, these wires must be disconnected. firther tests will be supplied bu the gang but try the loose wire things first. There are 2 wires that have quick disconnects at the ends of rhen. they should be color coded

**bgk** · 11-22-2002, 10:12 PM

Thanks Scotty,
So I guess the vacuum explains why the tank did not leak when I pulled it off the bike. But I still don't know what "prime" is, and I still don't know why the fuel gauge doesn't work, after I carefully checked and re-connected the two wires and then carefully re-installed the tank while making sure that the wires stayed connected.
Any ideas, anyone?
Thanks.

**focus frenzy** · 11-23-2002, 12:14 AM

If your petcock has two lines going to it, one smaller than the other, then you have the automatic petcock.
with the lever pointed foward, it is on reserve, pointed down is on and prime is to the rear.

one of the wires that go to the fuel gauge sending unit should be yellow with a black stripe, using a multi-meter, and the ignition switch turned on you should read voltage on this wire. If you do, then take the wire and momentaraly, for a instant touch it to the black with a white stripe wire, the needle should jump.
If you dont read any voltage on the yellow wire the gauge is bad, if you read voltage and the needle jumps then the sending unit is bad.

**Anonymous** · 11-23-2002, 05:37 AM

Originally posted by focus frenzy

If your petcock has two lines going to it, one smaller than the other, then you have the automatic petcock.
with the lever pointed foward, it is on reserve, pointed down is on and prime is to the rear.

one of the wires that go to the fuel gauge sending unit should be yellow with a black stripe, using a multi-meter, and the ignition switch turned on you should read voltage on this wire. If you do, then take the wire and momentaraly, for a instant touch it to the black with a white stripe wire, the needle should jump.
If you dont read any voltage on the yellow wire the gauge is bad, if you read voltage and the needle jumps then the sending unit is bad.

ill be the first one to thank you for that test FF

**bgk** · 11-23-2002, 12:28 PM

Focus Frenzy,

Thank you. I checked with the voltmeter per your instructions, and got zero voltage at the yellow/black wire, (with the key on, connecters pulled apart between tank and bike, voltmeter black lead on negative battery terminal, voltmeter red lead inserted into the black/yellow wire connector at the "bike-end" half of the connection, is this right?). So I guess the gauge is bad. What next? How do I diagnose/repair the gauge, or is it a non-repairable item that should be replaced via salvage yard used or Suzuki dealer new?

Also, although not of significant concern, I insist there is no Prime position for my fuel petcock lever. It will not rotate more than the 90 degrees I described in my previous post, between RUN (vertical pointed down) and RES (horizontal pointed forward).

None of this is critical, because I can always ride without a fuel gauge, and without knowing what Prime is, it's just that I'm curious and like to make things right.

Thanks!

**Anonymous** · 11-23-2002, 01:04 PM

I have no experience with your particular model, but I think these to be universal truths: If you have only one tube/hose leading to your petcock, it is a manual petcock, and must, by definition, have an 'off' position. If you have two tubes/hoses leading to the petcock, it is a vacuum operated petcock and must have a prime position. A vacuum operated petcock turns itself OFF at any time that the engine is not running, therefore it must have some provision to be turned ON manually to fill the carb bowls when they're dry (otherwise you'd never be able to start the bike again if you ran out of gas!). This manual override of the automatic off is called the "prime" position (I've always seen it abbreviated on the petcock as "pri"). As to a manual petcock, it will have one or two on positions that function as 'on', and one "off" position. A manual petcock must have an "off" (marked or not) or there would be no reason to have a petcock or lever! I hope this helps.

**bgk** · 11-23-2002, 03:31 PM

Now, I'm completely baffled. (By the way, I just returned home from a beautiful 2-hour Saturday afternoon Suzi GS ride in sunny New England, 40 degrees F, blue sky, just like a day at the beach!)

I definitely have two hoses connected between my fuel tank and petcock, one a little bigger than the other, just like Focus Frenzy described (plus another vent hose that drains below the airbox).

But I absolutely, positively do not have a Prime or Off position on my petcock (I'm really, really sure about this, I've triple-checked and even tried to gently "force" the petcock lever beyond the 90 degree arc between Run and Reserve that I previously described, with a pair of pliers!).

I'm guessing that a previous owner must have replaced the petcock with something different than OEM. Now I'm worried that if I ever do run out of gas, I'll never get the carbs primed. This post thread all started with a simple innocent curiosity about seeing the word Prime in this GS Technical Forum, and having a simple desire to fix my fuel gauge, because these GS bikes have fuel gauges, even though lots and lots of other bikes do not.

Can anybody help me solve my original worry about fixing my fuel gauge, or my new worry about running out of gas someday, and not being able to prime the carbs to get re-started?

Thanks again!

**Anonymous** · 11-23-2002, 07:33 PM

I know you just put it back on, but . . . Pull the tank. Hold the tank upright and turn the lever to one extreme. Does fuel come out freely from the big hose? Now try the other extreme. What happens? What I would expect to see (not an expert) is fuel coming out freely in one position, and no fuel in the other. Now, place the petcock in the no fuel position. Then apply some suction to the small hose to the petcock (by mouth should work). Does this cause the fuel to begin flowing from the other line? If so, the 'no fuel' position is actually the 'on' position, and the position that allows fuel to flow freely is the 'prime' position. Let us know the result of this testing. PS - My '81 has on/res/pri, but the '80 model of the same 1100 has only on/pri (and the fuel gauge to help avoid running out of gas). By the way, I know we've talked lever position a lot, but what markings are on the face of the petcock, ie: on/off, etc.?

**focus frenzy** · 11-23-2002, 08:23 PM

Well it is posible that the 79 "L" model did not have a prime posision.
As for the gauge, you can tey a used one or a new one, it's up to you.
But first, trace the wires up to the gauge and make sure that all conections are good first before you look for a new one, you could have a bad connection, or broke wire.

**Anonymous** · 11-24-2002, 07:09 AM

Re: Fuel Petcock and Fuel Gauge Questions

Originally posted by bgk

First question (just curious): I've seen references to "prime position" on the fuel petcock on the GS Forum. My petcock lever moves only 90 degrees, with a "Run" position with the lever pointed straight down, and a "Res" (reserve) position with the lever pointed straight forward. Where is "Prime" and where is "Off"?
Thanks

Most of the replies to this part of your post don't recognise the earlier petcock. The one you have has only the two position with no prime.

Later, from 1980 onwards, they had the three position petcock. I have the two position model described in my service manual. It has no handle but what seems to be a simple screwdriver slot.

If you would like the info page send me a PM and I will scan it for you.

Kim

**Anonymous** · 11-24-2002, 08:38 AM

FWIW dept;

kkmiller

I have a 1977 GS 750B-the very first GS model, and it has the three position petcock.

It does seem odd to not have a PRI position though...

**redliner1973** · 11-24-2002, 08:54 AM

Your petcock has probably been replaced sometime in its life with a generic on-off type.

kz · 11-24-2002, 09:31 AM

If you want to check the fuel gauge more in detail, you can measure the resistance for the different positions; the fuel gauge must be dismounted.

Unfortunally I only have the resistance length values for the 19 and 24-liter tank.

As an example I put the spec. for the 19 l tank, the figures are in the service manual, if you are interested I am sure someone here can provide it for you.

http://medlem.spray.se/ocorsagsi/fuelgauge.jpg

I think the GS 1000L has a 15-liter tank (total volume) with 3-liter reserve, so you must have at least as stock have an ON and RES position.

I have experienced that the lever on my former GSX 1100 1981 was very hard to move into another position, I had get off the bike if I wanted to turn the lever. I also think there must be a prime position on the GS1000L, at least as stock.... :?

**Anonymous** · 11-24-2002, 10:04 AM

Try this, I think the reserve position does not need vacom to open, thus, to prime the carbs, turn to reserve. Then back to on for normal use.

Fuel Petcock and Fuel Gauge Questions

Fuel Petcock and Fuel Gauge Questions

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