Gas Cap Modification

[fjr183]

??? Anyone! The gen-1's have fuel returning from the fuel rail and the gen-2's do not.

What effect does this change have on the fuel cell venting and gas cap venting??

Fred G

 

[Fred W]

I'm pretty sure I don't understand exactly what the little ball does...
BUT, if it has anything to do with stopping fuel flow OUT of the tank one needs to think long and hard (actually, short and simple suffices) before messing with it. The risk of crashing and having gasoline run out of the cap onto the pinned rider or passenger may or may not be slight but the other side of the equation is that the result can be horrific - and it doesn't take much leaked gas to do it.

Bill

I don't think that the check valve has anything to do with limiting spilled fuel. Rather, it appears to be there to prevent gasoline vapors from easily escaping from the tank for evaporative emissions reasons. If raw fuel were to find it's way through the pinhole and tiny labyrinth passages of the inner gas cap vent it would merely end up in the vent line hose. In the case of CA models that vent line goes off to a charcoal canister. In other 49 state models it goes to the underside of the bike.

There is always a chance when you ride a motorcycle that you would have gasoline spilled during any crash. After all, you are riding around with ~6 gallons of the explosive stuff tucked up between your legs. I don't think that this increases the chances greatly enough to be of any concern. For decades before the advent of emissions regulations, motorcycle gas tanks have had direct vent lines to outside air. Can't recall a single instance where fuel spilling from a vent line cause rider (or passenger) conflagration.

But feel free to worry about it if you like. If you do not feel safe doing this mod, then by all means, don't do it!

It should not need to be said, but as is the case in any "unauthorized" modification that one makes to their machines, you proceed at your own risk.

 

[twodogs]

Can't recall a single instance where fuel spilling from a vent line cause rider (or passenger) conflagration.

I can; from a defective/modified motorcycle fuel cap resulting in a literally terrible injury. And a death from a similar but seperate tractor overturn incident.

But feel free to worry about it if you like.

Thanks.

If you do not feel safe doing this mod, then by all means, don't do it!

Agreed.

It should not need to be said, but as is the case in any "unauthorized" modification that one makes to their machines, you proceed at your own risk.

Agreed here too.

And, as to the risk equation here, I agree that the increased chance of becoming burned beyond recognition as a human or dead in a modified gas cap gas leak fire is likely very slight - especially if the little ball "thingee" doesn't check fuel outflow, etc.... (all of which is apparently unknown at this point). However, the magnitude of that unlikely result is enormous. So, too much risk for me.

But, feel free to not worry about it if you like.

 

[Fred W]

Damn!! Who gave you my picture?

Here's a better one:

 

[user 213]

Geeze Fred, look what you've stirred up now. It's not like you mounted a CT or anything, it's just a little ball in the vent system!

Heck, you might as well mount a CT now. You've already been branded as a reckless risk taker.

 

[wfooshee]

??? Anyone! The gen-1's have fuel returning from the fuel rail and the gen-2's do not.
What effect does this change have on the fuel cell venting and gas cap venting??

Fred G

Not a damn thing. The Gen II only actually draws the amount of fuel it's actually going to feed the engine, the Gen I draws as much as it can and returns that which did not enter the injectors. In both cases a certain amount of fuel disappears from the tank over time, because it was burnt in the engine. That reduces the volume of fuel in the tank (obviously) but if the tank is sealed and pressure-tight, it creates a vacuum. A pressure tight tank would also pressurize as it heats up, from engine heat or just being out in the sun. neither is desirable, so the tank must be vented to the air. We don't want that vent to be so crude as to allow gasonline to spill out, or dirt, bugs, or other crud to get in, though.

 

[twodogs]

Damn!! Who gave you my picture?

An admirable good-humored response.

As to the question posed, well, I wasn't going to say but because you asked so nicely and used the cute little "unsure" face thingee:

I searched google images for "moron".

Here's a better one: [pic omitted]

As always, I'll be the judge of that.

All my best,

Bill

 

[wfooshee]

Holy cow. This shit just happened to me, starting last week. Went to fill up, got a big hiss on opening the gas cap. Went back home, did all the stuff to clean it up, found all the passages clear, found the vent tubes clear (could run air through them from my compressor) so I figured I took care of it. Went back to the station, hissing again! WTF??!!!

Went ahead and filled up, got home and removed the check ball.

Rode a good bit today, hottest day I've been out on and done any miles, and when I opened it, HUGE pop of visible vapor and hissing! Remember, the check ball is gone! Closed the cap, let it vent slowly. Closed it again, let it sit about ten seconds, and it hissed again when I opened it, pressurized that quickly in the heat!!

Brought it home, took the cap apart again, doesn't look any different than before. Push air down the drain and vent, don't get any through the vent tube! that's odd, I did before . . . . .

Lift the tank, and I can push air through the vent tube. Now that's just a bit strange!

Examined the tube, found a place where it had doubled back on itself, and was relieved by lifting the tank. My first check last week was with the tank up, explaining why it was clear then.

I think this started because I reinstalled the heat blanket under the tank, having removed it during the winter. Actually, not so much removed, as not bothered to reinstall it after a TBS in February. When I dropped the tank back down I musta kinked that hose and not noticed it.

So. Check the vent wthout lifting the tank, because the tube might be doubled over if you're as stupid as I am.

Oh, yeah: I went ahead and put the ball back in.

 

[Fred W]

Thanks for posting your experience, Walt.

Just out of curiosity, do you still have the 2 hoses being restrained by the little, uhm... restraint on the left side of the tank? Just trying to visualize how/where that vent line might get pinched.

 

[wfooshee]

The hose had pulled up into the space under the tank, probably got caught by my hand as I was laying in the heat blanket. It kinked right under the connection into the tank, kind of one pleat of an accordion-fold. All I had to do was pull the hose through that guide you speak of so there wasn't any "extra" in the space under the tank.

 

[David Morrow]

I've had the pressure build up happen several times. The big whoosh is certainly unnerving. I have an auxiliary tank on my 2003 FJR and the first time is happened, my main tank was down to about half full, I leaned back and opened my aux tank petcock to refill the main. With the pressure having built up in my main tank, the pressure forced fuel from the main tank back into an already full aux tank, and gas was then forced out the aux tank vent. My GF was riding behind me and spotted the problem and got me to pull over. Hell of a lesson for the first time I learned about the venting problem.

Another lesson : I disassembled my cap assembly per the above details. While I was at it, I figured that the venting orifices in the part of the assembly that were not taken apart may also need a bit of cleaning. So, with a aerosol can of carb cleaner with attached tube, I shot a little cleaner down one hole and it dutifully shot out the other. After a few times doing that, I hoped that it would have dissolved and flushed out any varnish therein which may have added to the venting problem. What I wasn't thinking about was that the carb cleaner would attack the rubber seal which of course it did. Said rubber seal cannot be purchased separately according to the online parts fiche and my local dealer. A new cap assembly is $200 +/- depending on where you shop. The good news is that overnight, the rubber seal regained its former shape and I think I'm out of trouble. If I find that the seal is well and truly buggered, I'll probably buy one of the aftermarket keyless cap assemblies from PIrates Lair . YMMV.

PS. The disassembly / reassembly is a piece of cake. Don't be nervous, do it at a clean, well lit work area and take your time.

PPS. If you remove the little ball bearing, and you decide to put it back after you've lost it, it should be easy to find a new one - the diameter is .1875" / 4.760mm. It's not a very tight fit

 

[SFCJCA]

I've had the pressure build up happen several times. The big whoosh is certainly unnerving. I have an auxiliary tank on my 2003 FJR and the first time is happened, my main tank was down to about half full, I leaned back and opened my aux tank petcock to refill the main. With the pressure having built up in my main tank, the pressure forced fuel from the main tank back into an already full aux tank, and gas was then forced out the aux tank vent.

Same thing just happened to me this past weekend. Opened up the petcock and started smelling gas. When I got home, I checked the vent line. It was clear. I guess it's time to try the ball removal and/or test to see how restrictive that restrictor is.

 

[Constant Mesh]

I disassembled my gas cap to reduce friction during key operation.

I followed Fred's commentary and photos.

I disagree with Fred a bit about some of his comments.

I believe the hole in the bottom of the latch assembly is likely a drain for gas which sloshes up into the mechanism.

Gas fumes would easily pass through the mechanism via the air gap created when the gasketed spring-loaded component is pushed up when the cap is closed.

The plate beneath the latch assembly does not move when the cap is closed but the gasketed component does move creating an air/fume gap around the total circumference of the fixed plate.

Since this fixed plate is held tight to the two vent orifices by the screws most/all of the fumes pass through the two small notches on the edge of the orifices.

If those small notches were plugged it would be difficult for air/fumes to enter or leave the tank.

The ball bearing would always be in the down, open position, unless there was a very rapid positive pressure situation. Possibly the bearing could stick in the up, closed position, if it became covered with sticky fuel sludge. Of course, every time you open the cap the bearing should change position if it isn't covered with crud.

Those two small notches would appear to be very important.

Some small flow could likely leak through the gap between the screwed down plate and the orifices but the notches would appear to be the key to good air/fume flow.

The gasketed spring-loaded component wasn't moving as freely as I believe it should. After taking it apart I discovered there was quite a bit of sliding friction between it and the cap casting. The casting was no longer smooth and the gasketed ring was not sliding smoothly past it each time the cap was opened/closed. I tried to smooth the casting a bit with sand paper. After sanding the gasketed ring moved freely again.

 

[Fred W]

Not sure exactly what you disagreed with me on since I never said anything about the gaps at the bottom of the cap except that there was plenty of space to vent through them. A prior post had inferred that we needed to enlarge those gaps, and my position was that this was not the cause of the gas geyser problems.

The ball is clearly a check valve on a vent that is intended to be open normally, but since tanks were developing pressure, it was malfunctioning by sticking closed at times. That was the point of removing the check valve ball, to eliminate the failure mode. Never heard of a gas geyser on any tank that had been castrated.

There were also never any problems reported associated with removing the ball, like were forecast, such as fuel leakage after a drop. Just like there were never any problem with the hundreds of thousands of bikes produced before emissions regulations nazis restricted free venting fuel tanks.

Im sure we all breathe so much better because gasoline vapors are held inside all of the new motorcycle gas tanks with their evaporative emissions restrictions.

But thanks for recalling a 10 year old thread from back when we had things to discuss.

 

[Uncle Hud]

If anybody knows what happened to beeroux, this thread's originator, please PM me.