No fuel in carbs + fuel leak (overnight)

Hi folks,

1/ What does "PRI" stands for on the petcock ?

2/ since there`s only 3 positions and the 2 others are "RES"(erve) and "ON" I suppose that PRI is OFF...

3/ I`m asking because my bike (just got it) a 1992 XJ900 starts but only runs for a couple of seconds.
No fuel in the carbs (took out the overflow screw, it`s dry in there) and when I came back the next day there was a pool of fuel on the floor !

4/ I didn`t take a picture of my petcock, should have, but there`s something that seams odd, one fuel line is going to the carbs and another 2" long with a kind of screw in it ! is that how it should be ??

thanks

 

Oboy.

1. "PRI" stands for "prime" it bypasses the vacuum controlled valve and allows fuel to flow all the time. It's like turning the faucet on.

2. As above, "PRI" is full on; the exact opposite of off. "ON" and "RES" are supposed to be vacuum-operated; except...

4. That plugged line is supposed to be attached to a vacuum source (probably the spigot on your #3 intake manifold) to provide the vacuum signal to operate the fuel valve.

3: The way it's supposed to work is this: the petcock is vacuum operated, via that plugged hose, and when working properly will only flow fuel (in ON and RES) when receiving vacuum pulses from the motor. The PRI position is used to fill the carbs when the motor is off.

However, your little dilemma has uncovered another issue: the carb float valves should have shut off the fuel flow even with the petcock on PRI. If you got a puddle of gas on the floor, you probably also have a bunch in your crankcase as well. Open the oil filler and have a whiff; if it smells strongly of gasoline in there don't run the motor.

You're going to need to attend to your carbs (one or more floats not working properly) fix or replace the petcock, and then change the oil first.

 

On my 1981 XJ 650 Maxim, the Petcock has the same positions as you described.
PRI is not off, it is PRIME and allows gas to flow into the carburetors without any vacuum applied to the system.

One fuel line runs to the 'front' of the carb rack and one 'vacuum' line runs to the intake boot ('back' side of the carbs).

What did the PO (previous owner) tell you they worked on before selling it to you? . . . . Sounds like you have some motorcycle maintenance in your future.

Do not fret! There are many good teachers here that will guide you through the process.

Pictures are good.

 

thanks guys.

so I should:

1/ take a sniff at my oil filter and change the oil if it smell fuel

2/ try to find a picture or something and put that plugged line where it should be.

3/ take out the carbs and buy a carburetor rebuild kit

 

Close.

1: Open the oil FILLER CAP and have a smell. You need to see if your crankcase has been polluted with gasoline.

2: Yes. But you also need to check the functionality of the vacuum operated fuel valve. That plugged vac line is a clue to somebody's misguided attempt to fix something they didn't understand. You may need to attend to the petcock as well.

3: Sort of. You will need some things (o-rings, gaskets) but other things may be fine or may need to be replaced. You pull the carbs, tear them down, clean and inspect and then order the parts you need. Beware of cheap/poor quality "rebuild kits."

BEFORE #1 even: Find a service manual. You're going to need it. In order to properly adjust the freshly serviced carbs, your valve clearances will need to be in spec.

Then we'll talk about the 22+ year old brakes.

 

1/ close enough :lol:

2/ I suppose I`ll have to dig into that also !
how do you check that valve ?

3/ I`ve found this handy video https://www.youtube.com/watch?v=xavlIhHHWy8

I`ll look after a service manual @ the Jap meeting I was referring to in my other post.

about the brakes, I`ve read here that the hoses have to be changed every 4 years, and that the date up to whenthey are ok is on the hose, strangely enough mine is from 1992 and the hoses are dated 8/1990 !!

I`m planing to put some stainless lines, looks again...

 

The date codes on the lines are when they were made.

The fuel valve should flow fuel in "ON" and "RES" when vacuum is applied to the small hose. Disconnect the fuel line and put a container under the petcock. Apply vacuum to the smaller hose. I would recommend a small handheld vacuum pump rather than sucking on the line (which does work) because if the diaphragm has failed you'll get a mouthful of gas. It DOES NOT require much vacuum at all, be careful when using a pump.

Fuel should flow when vacuum is applied and stop when there is no vacuum.

 

great ! looks easy enough.

thanks for all your precious help !

 

ok so here`s a couple of pics of my carbs and petcock

 

Which may be why there's a screw in the line. But you never know what the previous owner was thinking.

 

I was actually expecting to see the vacuum hose connected to the petcock and the other end of the end of the vacuum line have a screw in it.
There should be two ports on the petcock, one that the fuel line is attached to and the other is for the vacuum hose. Remove the screw from the hose and connect it to the other port on your petcock. Then the fuel should only flow when "ON" or "RESERVE" only when the engine is running. If it doesn't work properly like that then you'll need to rebuild the petcock.

 

You also need to run the fuel line so there re no kinks in it.

 

Yeah no kidding. The fuel line is obviously kinked.

The line with the screw in it is what we thought, it's the vacuum line to the #3 intake manifold's vacuum spigot.

But where is the vacuum connector on the petcock? Maybe it's just the pics, but I see no place to hook up the vac line; we need to see the back of the petcock.

It looks like a stock Yamaha petcock; we need to see what might have been done to it on the backside.

 

I`m going to take my carbs out today, I`ll take a picture of the back side, and no there`s no other port on my petcock, looks indeed like somethimg`s missing !

can you buy just that port as a spare part ?

 

took my carbs out, gonna rebuilt them to the OEM specs first

 

the PO apparently did cut the hose leaving it attached where it should on both sides...

 

Apparently.

Which would mean that the petcock should only flow fuel when in "PRI" since without a vacuum signal, "ON"" and "RES" shouldn't flow.

Your PO apparently didn't understand how it was supposed to work.

 

it indeed doesn`t flow on "ON" nor "RES" the is on the ground now with the fuel hose just hanging there and no gas spilled...

so what should I do now? just take care of my carbs and when they are done put a new hose where the PO cut it ?

 

Test the petcock. GENTLY apply vacuum (suck on it GENTLY) to the "signal" hose with it in "ON" or "RES" and if gas flows when vacuum is applied and stops when vacuum is released the petcock is working properly. If it works properly, then yes, replace the cut hose (with real vacuum line) and be done with it.

Your PO probably (and incorrectly) diagnosed his float issue as being petcock-related. A common mistake.

 

is the signal hose the that`s cut ?