fuel leak from overflow tubes

[indyblue]

My '84 FJ1100 leaked after riding this spring and I ran a few tanks of gas with cleaner and it stopped.  I guessed that varnish was keeping the vacuum valve from closing all the way and drip...drip...drip.

It's been dry all summer long and last night I parked and come out to the garage this morning to a large puddle of gas on the floor.  I went and turned the stopcock to the "OFF" position and it is still dripping.  What gives?  I have a new valve/diaphragm from RPM sitting in the toolbox, but why would gas keep flowing to the carbs if shut off?

[TexasDave]

It is time to replace the petcock if you have a new one. With age the rubber diaphragms and seals will age and crack. I don't trust the carbs to stop the fuel flow alone as you can see by your gas puddle. What is worse than the puddle on the floor is flow through the carbs into the cylinders and down into the crankcase. I would check the dip stick for the smell of gas in the crankcase. Also safety wire the petcock when replacing.

Dave

[ZOA NOM]

Do it now.

[indyblue]

The oil level in the site glass is normal, I keep an eye on it and luckily I think the overflow tubes are doing their job keeping the gas out of the engine.
I figured if the diaphragm had a tear it would drip all the time, but it stopped after the first tank of gas with cleaner in it.    I think the needle valves/floats are ok, carbs all look like new inside.
I guess the new diaphragm needs to go in and I wired the petcock years ago upon reading the horrors on this site.

[Pat Conlon]

I went and turned the stopcock to the "OFF" position and it is still dripping.  What gives?  I have a new valve/diaphragm from RPM sitting in the toolbox, but why would gas keep flowing to the carbs if shut off?

I don't recall my '84's vacuum petcock having an "off" position.
The lever has 2 positions, on and prime......again, going by my memory.

Get thee a new petcock, and be safe and change your oil. Even a teaspoon of fuel will breakdown the oil.
If you buy from RPM the petcock will already be safety wired. Randy does not fuck around with this issue.
http://rpmracingca.com/proddetail.asp?prod=M%2FC%3A36Y-24500-01

Cheers. Pat

btw Indy, your '84 is unique and beautiful, absolutely beautiful.

[fjbiker84]

My 84 has experienced this problem several times.  The first few times this happened to my bike, I ordered a new OE petcock (BTW, they don't have an off position) and installed that. However, every couple of years this problem would seem to pop up again (even with relatively new petcocks) and I'd discover a puddle of gas under the bike.  The last time this happened was at the 2017 WCR. Randy, of course, was there and looked at my bike.  He thought the problem was with the drainage tubes running from the carburetors.  There is a specific location for these tubes to run behind the engine and there is a metal guide there to hold them in place.  Randy thought that improper routing to the tubes could cause pressure to build in the fuel system and allow the petcock to remain open even when the bike is shut off.  After re-routing the tubes correctly and riding the bike home the following day, this problem has never happened again.   

[Hersey289]

Maybe the following helps as well...

I purchased a new petcock from Randy 4 or more years ago for my '85 FJ1100. On two occasions (about 2 years interval), the petcock leaked fuel which I found out when taking the tank off and disconnecting the fuel line from the petcock. Fortunately, I didn't have fuel leak out the overflow tubes as my needle/seats held. So... I disassembled the petcock both times, and found that small metal flakes from the internal casting fouled the sealing surfaces of the rubber sealing disk. I was able to easily clean this contamination off, then applied some grease to the disk and reassembled the petcock assembly. The petcock worked perfectly afterwards.

Rob

[Motoguy]

On my FJ it would piss out gas after I parked. Turned out to be gas leaking around the o-ringsof the plastic holders that hold the screens for gas input to carbs. Float height and cut off valve were good but those o-ringsof were drier than a popcorn fart. $22 kit from R.P.M fixed me right up.

[balky1]

On my FJ it would piss out gas after I parked. Turned out to be gas leaking around the o-ringsof the plastic holders that hold the screens for gas input to carbs. Float height and cut off valve were good but those o-ringsof were drier than a popcorn fart. $22 kit from R.P.M fixed me right up.

I suppose you are talking about the needle seat O-rings.

[indyblue]

On my FJ it would piss out gas after I parked. Turned out to be gas leaking around the o-ringsof the plastic holders that hold the screens for gas input to carbs. Float height and cut off valve were good but those o-ringsof were drier than a popcorn fart. $22 kit from R.P.M fixed me right up.

I suppose you are talking about the needle seat O-rings.

This is what's happening to me, after I park it leaks.
My petcock has 3 positions, Off, Prime, and On.  (You can just barely see the "F" of OFF on top)


So which O-rings do I need?  I believe the needles/floats are holding and it is leaking in the Off position.  If it were the o-rings to the carb input, why would it leak if my petcock if OFF ( I could understand a few drips after shutting off as the bowl level goes down)?

I already have the RPM vacuum diaphragm kit, is there another one?

BTW, the parts finder on my local dealers website shows a petcock available, it has a superceeded part # on it:
    https://www.partshark.com/oemparts/p/yamaha/36y-24500-01-00/fuel-cock-assembly-1

[racerrad8]

On my FJ it would piss out gas after I parked. Turned out to be gas leaking around the o-ringsof the plastic holders that hold the screens for gas input to carbs. Float height and cut off valve were good but those o-rings were drier than a popcorn fart. $22 kit from R.P.M fixed me right up.

This is what's happening to me, after I park it leaks.
My petcock has 3 positions, Off, Prime, and On.  (You can just barely see the "F" of OFF on top)

I do not believe you have a three position petcock. If you look closely the letters you are referring at the top are "EL" the last two letters of "FUEL". The FJ1100 petcock is two positions as already mentioned; PRI (prime) and ON. The PRI (prime) function is too fill the carb bowls if you work on them or run out of gas.

The "ON" is the normal operating function. The fuel flow is control by the vacuum diaphragm & o-ring inside of the petcock. That is what the petcock rebuild kit you bought from me is designed to replace.

If you look very closely at the edge of the lever you can see an arrow. That arrow in that position is pointed straight down indicating the petcock is in the "ON" position.

You can see the arrow very clearly on the new petcock here just under the "FUEL" lettering cast into the lever.

So which O-rings do I need?  I believe the needles/floats are holding and it is leaking in the Off position.  If it were the o-rings to the carb input, why would it leak if my petcock if OFF ( I could understand a few drips after shutting off as the bowl level goes down)?

You have a couple of options for carb o-rings; A complete carb o-ring and S/S allen head screw kit, a full carb o-ring kit or just the needle seat o-ring kit. You can see them by clicking the links below.

FJ11-12/XJ12/XJR13 S/S Screw & O-Ring Carburetor Kit
FJ11-12/XJ12/XJR13 O-Ring Carburetor Kit
Needle Seat O-Ring Set

BTW, the parts finder on my local dealers website shows a petcock available, it has a superceeded part # on it:
   https://www.partshark.com/oemparts/p/yamaha/36y-24500-01-00/fuel-cock-assembly-1

Get thee a new petcock, and be safe and change your oil. Even a teaspoon of fuel will breakdown the oil.
If you buy from RPM the petcock will already be safety wired. Randy does not fuck around with this issue.
http://rpmracingca.com/proddetail.asp?prod=M%2FC%3A36Y-24500-01

Cheers. Pat

As Pat already mentioned above as well, the new Yamaha petcock is available from RPM. By comparing the link to your local dealer website, you will save a few bucks buying it from RPM. Plus you will get the benefit of the petcock elbow being safety wired when you buy on from me. Plus, it is in stock and can be shipped to you in just a couple of days time. No waiting a week or more from the dealer.

Here is again is the link to the 85/85 FJ1100 Petcock:

84-85 Yamaha Fuel Tank Petcock


If, by chance, your petcock does say "OFF" on the top of the petcock, I would like to see that so I can make some inquiries on what petcock that might be.

Randy - RPM

[indyblue]

You are correct, upon closer inspection it does say FUEL.  But what is that 3rd position then? 

If it were the needle valve o-rings, where would the fuel go?  My service manual section view (pages 4-2 to 4-4) doesn't clearly show the overflow system and I can't really see where the tubes connect on the diagram.

Presumably it would flow through the lowest point in the fuel circuit, not sure if that's the overflow outlet or the venturi's.  It would make sense for the overflow to catch it before it makes it to the intake.

The last time I was inside the carbs was 3 years ago where they looked brand new inside (no visible varnish anywhere) and the needle valves appeared new and the rubber nice and pliant. Due to it running a bit rich, (I think the main jet is too big) I lowered the float level to almost the lowest tolerance to account for it (I think someone here gave me that idea).  That would point to the needle valve o-rings and should prob be my next step. 

It runs very well otherwise even though my Supertrapps turn black halfway through the season, at least it doesn't fowl after 100 miles anymore.

[Pat Conlon]

Don't over complicate it.
Turn the petcock to the on position.
Remove the fuel line.
If the petcock drips fuel, any fuel, it's broken. Bad o rings.

Now check the vacuum open/close actuation of the petcock.
Put a piece of fuel line back on the petcock fuel port and run the end to a gas can.
Disconnect the vacuum line.
Put a piece of clean tubing on the petcock vacuum port.
Lightly suck on the tubing, the petcock should open and fuel should flow, a good strong flow.
(we call this the suck test)
If the petcock opens, good, now while lightly sucking, place the tip of your tongue over the opening in the tubing. (I did mention that this vacuum tubing should be clean)
The petcock should hold a light vacuum. If it does not and the fuel flow stops, then you have a leaky vacuum diaphragm. You should never be able to draw air thru the vacuum line when connected to the petcock.

Stop sucking, the fuel flow should stop. As in totally stop with no drips.
Do this several times to make sure it fully opens and fully closes correctly.

You can take the chance on rebuilding it, putting in new o rings and a diaphragm, hope for the best.
We are lucky that new oem petcocks are still available. I took the easier softer way and just got a new one.
Regardless of which way you go, safety wire the elbow.

Petcocks live in a tough environment exposed to the engine heat.
I think of it this way: Getting 34 years of life out of the petcock is not a bad deal.

Fix your petcock first, then see if you need to do anything with your carbs.

Cheers.  Pat

[red]

Indyblue,

Your old petcock does not have safety wire around the L fitting, where the fuel tubing connects to the petcock. There is a sealant that should hold the fitting, not threads, but the sealant can get old and brittle after all these years.  Safety wire is a simple & cheap fix, to prevent the L fitting from separating from the assembly.    Check the RPM image, for comparison.  This can be a serious safety issue, so don't neglect it.

[copper]

Dan used to post a annual reminder, not sure if I've seen one recently here is one of his old ones. http://www.fjowners.com/index.php?topic=3251.0