Fuel tank vent

[Waiex191]

Hey all,
I searched and could not find much info, except that a few folks have said a plogged fuel tank vent will kill the bike.  I am pretty sure I'm there.  With the fuel line unplugged from the fuel pump etc, it would not gravity drain at all with 4+ gallons in the tank.  I did not think to pop the cap and see if that fixed the problem, and now I have the tank off and the fuel drained out.  Actually I was inspecting the inside of the tank with a borescope camera in case I had a dreaded Kreem failure.

So, how do I check and fix this?  Does the cap assembly have to come off the bike or do I do something to the part of the cap with the lock? 

In other threads I've posted that the bike runs poorly at WOT up above 7000 RPM.  I am wondering if this vent has been degrading and showing itself during high fuel flow.  I guess I'll find out soon.

I'm off to RPM to buy a new petcock o-ring and see what they have for vent stuff.

[Pat Conlon]

Cut open your fuel filter and have a look see...when (not if) you have a Kreem coating failure, the flakes will show up in your fuel filter and can also clog up your petcock.
The tank venting depends on if you have a Calif. model or not. (Check the VIN) The USA models have the simple relief venting in the tank caps. The Calif model have a more elaborate venting system.

[Waiex191]

It's a pretty new filter because of what the alcohol in the gas did to my carbs. I can easily blow through the filter. It is not a California model.

Do I take off all the allens to get to the vent?

[Pat Conlon]

It's a pretty new filter because of what the alcohol in the gas did to my carbs. I can easily blow through the filter. It is not a California model.

Do I take off all the allens to get to the vent?

(Going by memory) yes, the Allen's around the cap must come out, you will see only 2 Allen's actually secure the cap. Open the cap and you will see a 3rd Allen to take out, then the cap comes off the tank.

Under the cap you will see 2 screws that hold the lock mechanism to the cap, they could be Allen's or Phillips (JIS)
Please note:
*Before* you take the cap apart, do this in a 5 gallon bucket because there is a tiny spring and ball that is the detent mechanism for the lock flapper which will fly away, never to be found....and thus you will end up with a flappy flap which will be a topic of ridicule at the next FJ Rally.
*You must disassemble the cap lock in a bucket, trust me* (actually I did mine in my bath tub, but a bucket is better)
After you disassemble the lock guts you will see 2 small silicone diaphragm disks that are 1 way valves. You want to cut a pie slice out of each of these disks, or remove them entirely.
Reassemble accordingly.

Cheers.   Pat

[Waiex191]

Thanks Pat!  I'll report back on what I find and how it goes.  I have a couple of buckets available.

[FJmonkey]

FYI>>>

When taking the cap apart, watch the orientation of the plastic part holding the silicone flap check seals. Either put it back in the original orientation or leave it out. I found out, that even with the seals removed, the plastic part can cause a fuel starve issue if installed wrong.

[Waiex191]

The silicone check valves were old and sticky. I took them out. I did manage to lose the spring for the lock cover but I have the ball. 

[Waiex191]

FYI>>>

When taking the cap apart, watch the orientation of the plastic part holding the silicone flap check seals. Either put it back in the original orientation or leave it out. I found out, that even with the seals removed, the plastic part can cause a fuel starve issue if installed wrong.

Thanks for this hint.  I put it together right but was still having issues.  I took it apart to check and decided to remove the plastic part altogether.  It seems like the black rubber thing that seals the vent path was sagging and may have been sealing off the plastic body.  I have good gravity feed flow again but I have not got it all the way back together.

[Waiex191]

Bike is back together and running much better. Did a few pulls to redline in second gear. Still a little hokieness up high, so I think I need to check the ignition and kill switch as has been suggested.

[Pat Conlon]

I had an intermittent 7-9k rpm ignition studder traced to a dirty run/stop handlebar switch. To rule out a ground fault I ran a temp ground wire from the battery ( - ) to the TCI box, went for a ride.. the problem remained.
Next I ran a temp jumper wire from the ( + ) battery to the TCI, rode the bike, and the problem went away.... Then I traced the + power circuit thru the key switch, fuse block and the run/stop switch....that's how I found that rascal.  
Because the problem was intermittent (high rpm) it did not show up with the typical continuity, voltage or ohm circuit testing done in my garage, I had to road test.

Cheers.   Pat

[Waiex191]

I had an intermittent 7-9k rpm ignition studder traced to a dirty run/stop handlebar switch. To rule out a ground fault I ran a temp ground wire from the battery ( - ) to the TCI box, went for a ride.. the problem remained.
Next I ran a temp jumper wire from the ( + ) battery to the TCI, rode the bike, and the problem went away.... Then I traced the + power circuit thru the key switch, fuse block and the run/stop switch....that's how I found that rascal.  
Because the problem was intermittent (high rpm) it did not show up with the typical continuity, voltage or ohm circuit testing done in my garage, I had to road test.

Cheers.   Pat

Pat,
How bad was your switch?  Mine showed a little oxidation but nothing major. It's shiny clean now but I have not had a chance to road test it.

[Pat Conlon]

When I opened it up I remember thinking that it didn't look that bad, but I cleaned and regreased it anyway.
No troubles since.
Note: The spray contact cleaner used for electronics will turn your red rocker switch pink.

I never use the run/stop switch anymore. I shut off my engine by using the side stand switch, that way I know my side stand is down before I dismount my bike (don't ask)...now if I can just remember to turn my key off.....

[Old Rider]

Pat  i have rewired  the switch for my sidestand so i can use it as a kickstarter     just a bad joke again