Gas Cap Modification

Well I remember my first ride with the excellent Tanji fuel cell. I was streaking along the Mojave outback headed for the Twist and Shout rally staging in Flagstaff, AZ. I'm bopping along when I notice headlights and horn behind me. I slow down and the car pulls up to my left in the opposing lane, the passenger pointing frantically towards the rear of my bike. WTF?

I pull over, dismount and walk back to see a very strong and steady stream of gasoline pouring out of my fuel cell vent line. DOH!

Good thing I routed the hose correctly. It dispensed gas away from the muffler and wheel. I threw the cell valve to off, which stopped the gas flow. I was stumped.

Jump back on the bike and ride off towards Needles, CA. I stop to get gas, seeing that I just lost quite a bit, and was very surprised when I opened up the gas cap and gas in its liquid state came screaming out and all over my face and everything. WTF?

Sadly, this went on for months. I blamed the cell, myself, the gods, everything but the gas cap. Then one day just before White Pine Fever, I was talking to IBA Technical Advisor Tom Austin. I had finally suspected the cap after taking it entirely apart ( not recommended for the faint of heart ) and cleaning every small passageway and oriface. He mentioned that in 2002, the Department of Transportation mandated that every motorcycle sold in America, 49-state bike or not, needed to have a system whereby a nominal amount of pressure could be built up in the tank to keep errant gas vapor out of the atmosphere.

Yamaha did this on the FJR via springs against a plate inside the gas cap. A brilliant feat of simple engineering. Problem on my bike anyway is that the spring pressure to relieve the pressure is phenomenal. I could barely actuate it with my hands. Other gas caps proved to have similar strength springs.

On a bike without Aux. Fuel, it works fine most of the time. Add a cell, and you'll be visited by grief at nearly every turn. This affects every known brand of cell on the FJR, no manufacturer is immune. So, what to do about this excessive pressure?

Annie get your drill.

Picture #1



This is a view of the cap flipped up. For now, ignore the half circle you see underneath the latch "ramp". Atop ( in the pic ) the cap see the rounded rectangular hole below the marking E1? Thats where pressure from the tank enters and eventually defeats the springs, allowing the plate shown below to open and allowing pressure to escape via the vent line attached to the orange rubber nipple in your cap recess.

Picture #2



This picture shows the plate that is held in place by the screws and stand-offs. It allows the plate underneath ( shown below ) to move and vent pressure.

Picture#3



Looking at the top part of the cap in this picture, notice the keyhole shaped cut-out in the plate, and the small hole on the left. This hole is connected via intricate passageways to the small hole found in the lower right of the cap that mates over the orange rubber nipple, and normally carries a small steel ball that acts as a check valve of sorts. I removed mine. On my bike anyway, this plate never moved before sufficient pressure was built up and would expel gas out the cell. Not good. CAUTION: after removing the 2 screws holding the latch mechanism, remove the latch CAREFULLY, or you'll lose a small spring and god help you figure out getting it back in.

So looking at picture #2, we see 4 holes. The 2 smaller outboard holes are for the screws, the two larger inboard holes are inlets for venting and pressure relief. While the springs are holding the "keyhole" plate tight to this plate, no venting or pressure relief can occur. Springs depress, the 2 larger holes allow pressure to vent, and all is good. Good, unless your springs are too stiff and the thing never vents.

See on picture#2 in the top center, the wear marks of the latch mechanism? Drill the smallest hole you can half in and half out of the wear mark. The smallest hole is all you need. Think 1/64 or less if you have it. This is seen clearly in picture #1. In hindsight, I drilled WAY too large a hole. When its hot and I'm moving fuel forward from the cell, I can smell gas. It's nowhere near strong enough vapor to ignite, and at speed I can't see it being a danger.

I have NEVER had liquid fuel come out the cap EVER.

I MUST advise that this information is provisional only, and that I have since replaced my drilled plate back to an un-drilled stock plate.

George Zelenz

March 17, 2007

Very, very interesting. I've been to the stage where I took things apart and stood there sort of dumfounded with my father the long-time farmer. The 2002 makes a lot of sense and the description of the pathways makes sense.

I'm glad you put it back to stock. The mothership will be so happy

Gonna take another looksee myself.

Thanks my friend!

beeroux said:

Drill the smallest hole you can half in and half out of the wear mark. The smallest hole is all you need. Think 1/64 or less if you have it.

Click to expand...

Hi George,

I'm in on Skyway's aux cell group buy, so your topic definitely caught my attention.

Perhaps an alternative approach would be to file or scribe a shallow scratch in the top side of the plate you show in the second picture, between one of its venting holes to a position beneath the mating key hole in the plate above it. This would let you make an arbitrarily small channel to vent the pressure.

You didn't mention how things have faired with your aux cell since you've gone back to the stock gas cap plate. Are you still having venting problems? Or has the replacement plate somehow "fixed" it?

Cheers...

I think this filing idea is great. Go for it.

Like I said though, I myself have returned the cap to stock, got rid of my cell, quit riding, and am becoming a bible salesman.

GZ

OK, gotta ask. Couldn't a feller just remove the orange grommet and eliminate all over pressurization issues? The pressure would simply vent out the hole at cap bottom, (bottom of where grommet used to be) and not have to force the mango springs up to get through the cap? Wouldn't it simply vent excess pressure down the vent/overlow for 49 state bikes or to the charcoal cannister for Kali bikes?

Oh, GZ, it's good to hear you returned the cap to stock (15% restocking fee?), elimated your cell phone, quit riding the exercise bike, and have become a successful salesman for Gideons! :yahoo:

beeroux said:

I think this filing idea is great. Go for it.
Like I said though, I myself have returned the cap to stock, got rid of my cell, quit riding, and am becoming a bible salesman.

GZ

Click to expand...

Bible salesman I'll believe. Got rid of your cell, that I don't buy. Besides, the 11.4 gallon GS tank doesn't fit on the FJR....

Say, would it be possible to trim a coil or two off the spring that holds the plate 'closed'? I should add that during Spank, when I was sitting in the blazing hot sun waiting for Doug C. to get the Tagliagliphs (sp) bonus, I could hear my tank vent briefly, then a minute or so later, vent again, etc. Mine is working, but not quite as well as I probably could to avoid the occasional dreaded back pressure event, which I have only experienced once after riding 40 miles of gravel road and on a 100F+ day. (I also have a Tanji cell, fwiw.)

dcarver said:

OK, gotta ask. Couldn't a feller just remove the orange grommet and eliminate all over pressurization issues?

Click to expand...

DCarver, an excellent question.

Unfortunately, the answer is no.

For those of you willing to be discouraged, not only take your cap off, but remove the lower plate and get straight to the tank. When I did this, I was AMAZED at how much dirt had collected there. Granted, I've been in the bowels of Anza-Borrego, ridden almost 1K "Off-Road", and live off a dirt road, but criminy was there a LOT of dirt gathered under the "seal" and cap assembly.

Sadly, with the orange nipple removed, all that dirt would be going into your tank, and only so much of that will be caught by the filter before it fails.

In effect, you'd be circumventing the benefits of the intricate gas cap, and just sucking dirt straight from the get go. Drill or grind a slot and reap the benefits of pressure transfer without the downside of debris collection.

GZ

beeroux said:

dcarver said:

OK, gotta ask. Couldn't a feller just remove the orange grommet and eliminate all over pressurization issues?

Click to expand...

DCarver, an excellent question.

Unfortunately, the answer is no.

For those of you willing to be discouraged, not only take your cap off, but remove the lower plate and get straight to the tank. When I did this, I was AMAZED at how much dirt had collected there. Granted, I've been in the bowels of Anza-Borrego, ridden almost 1K "Off-Road", and live off a dirt road, but criminy was there a LOT of dirt gathered under the "seal" and cap assembly.

Sadly, with the orange nipple removed, all that dirt would be going into your tank, and only so much of that will be caught by the filter before it fails.

In effect, you'd be circumventing the benefits of the intricate gas cap, and just sucking dirt straight from the get go. Drill or grind a slot and reap the benefits of pressure transfer without the downside of debris collection.

GZ

Click to expand...

I must be missing the big picture... thought that the tank 'vents' via the charcoal filter for Kali bikes, or via the straight-to-atmosphere vent tube for 49 state bikes. I think. If it can vent vapors via that path, then it should also allow atmospheric pressure to reach the top of the tank, above the liquid gas fuel level, thus preventing vacuum/vapor lock?I thought the path from the tank via the orange grommet through the cap was only for overpressurization relief and not for allowing atmospheric pressure to the air portion of the gas tank? e.g. a one way path to relive pressure, not vent the top of the tank? I tried to 'blow' pressure through the cap, and it was sealed tight. More than my lungs could provide. So, if sealed, how would it 'vent' the top, non liquid volume of the tank?

I really need to look at mine tomorrow. My feeble cranium scareabelllium is venting excess smoke now.. No wonder I'm not an enJinR.

DCarver,

It's gonna take me an hour to decipher your last post.

But mere minutes for the Stone IPA to lay waste to yet another billion cells.

Ahhhhhhhhhh.<G>

I'll get back to you soon.

GZ

beeroux said:

DCarver,
It's gonna take me an hour to decipher your last post.

But mere minutes for the Stone IPA to lay waste to yet another billion cells.

Ahhhhhhhhhh.<G>

I'll get back to you soon.

GZ

Click to expand...

LOL. Understand fullly GZ! I think I'll be purchasing a new cap myself since I ruined the orange grommet and apparently you can't buy it alone.. But I will say that since I tossed the grommet, and bypassed the Kali charcoal filter, my 2006 Kali bike is running MUCH better at slow speeds / throttle settings. No surging, no stalling, etc. Recall that at Beatty, it actually simply quit running. Had to keep r's at >3k to keep the fire lit. As a reference point, on my scoot, it takes more pressure to 'vent' via the cap than throgh the charcoal cannister. I'm very surprised at how much pressure it takes to vent via the charcoal cannister route..

..and now I gotta ask.. what the heck is a 'Stone IPA'??

LOL. Understand fullly GZ! I think I'll be purchasing a new cap myself since I ruined the orange grommet and apparently you can't buy it alone.. But I will say that since I tossed the grommet, and bypassed the Kali charcoal filter, my 2006 Kali bike is running MUCH better at slow speeds / throttle settings. No surging, no stalling, etc. Recall that at Beatty, it actually simply quit running. Had to keep r's at >3k to keep the fire lit. As a reference point, on my scoot, it takes more pressure to 'vent' via the cap than throgh the charcoal cannister. I'm very surprised at how much pressure it takes to vent via the charcoal cannister route..

..and now I gotta ask.. what the heck is a 'Stone IPA'??

Click to expand...

Yowza.

So what takes more pressure to vent, your cap or your canister?

Don't tease a drunk man.<G>

Your Cali-Can is NOT the problem. I'll bet a testicle it's a fuhqed gas cap.

Seriously. You posit that the orange nipple is to blame, yet removing it didn't solve your problem.

<waiting for that thought to shift into gear>

I like you Carver, but you're being lapped by an IPA toxified fool. Not good. ( for you )<G>

https://www.stonebrew.com/tasting/ipa/index.html

GZ

Well, fascinated by the problems listed here, just liking taking shit apart, and since Frank is all over the basement in chunks anyway, I pulled his cap and disassembled to see whats what. First off, a re-affirmation that 3M 08880 Brake Cleaner is orange grommet safe, soon to be prominently displayed on the can and in future ad campaigns The roll pin used at the cap pivot is plain, rustable steel, so pulling the rubber cap seal (large black surround) may reveal to you what I found: yucky rust staining the area. Trusty 3M to the rescue, all better now. Upon disassembling the cap, I found a few interesting things. First off, the spring loaded rubber sealing ring George mentions doesn't appear to have anything to do with venting-it's purpose is twofold-1 to seal the cap against the tank opening, and 2 to ensure the cap is fully shut to allow key removal. It's part of the interlock within the cap in that regard.



Depress that ring, and the key can be removed with the cap assembly off the bike. This is the spring you feel resisting cap closure. In any case, shooting the brake clean through the vent hole at the back of the cap asm showed the fluid flowed regardless of the position of that ring-extended or depressed (as if the cap were closed). Another thing I found was a piece missing in Georges pic and description-a steel check ball in the well pictured-



When the cap is closed, this ball falls, opening the passage to allow venting. Turn the cap (or bike) over,this ball seals the passage, preventing fluid from leaking out the passage. In any case, it would seem the big culprit in venting problems seems to be that which affects a lot of components on the bike-crud, rust, and the like. If that ball gets enough junk on it, or in the small well, it's conceivable that the check ball could stick at the top of the well, effectively sealing the passage, and getting ever tighter as pressure builds. Even a bumpy road could possibly pop it up into the well, with a little tank pressure doing the rest. Anyway, just another take on the issue-could be that removing that ball and ensuring the passages, both in the cap and the vent system beyond, are clean, that the grommet isn't distorted, swelled, or otherwise damaged so as to block the passage and prevent venting, is the key to avoiding problems in this area.

Note: If you disassemble the cap, and have the key removed, be aware that when reattaching the latch mechanism (final step) the key must be in the lock and the latch released, so that everything once again lines up. Ensure the plate just below the latch is flush with the base. Key in ensures this.

Radman,

DOH!

I TOTALLY forgot to mention I removed the ball at the time I drilled the hole. It's been awhile. Mine was stuck very tightly in place, being jammed from so much pressure. No gunk was found there.

And you're partially wrong about the springs intended uses. They ARE partly being used to vent, how else would you transfer pressure through the ball bearing oriface?

Hmmm?<G>

Thanks Rad for catching my mistake, back to the editor.

GZ

Excerpts from an earlier post where I had dissembled my gas cap:

This past weekend I pulled off the filler ring assembly and found an amazing pile of road spooge that I cleaned out.

Should anyone consider dissembling the gas cap assembly, be aware that there are 4 small springs and a check ball that are fabricated with Alakazam's fourth dimensional vanishing capabilities. If you take out the three screws that hold the lock assembly together, take great care not to let Alakazam disappear your parts.

beeroux said:

Radman,
DOH!

I TOTALLY forgot to mention I removed the ball at the time I drilled the hole. It's been awhile. Mine was stuck very tightly in place, being jammed from so much pressure. No gunk was found there.

And you're partially wrong about the springs intended uses. They ARE partly being used to vent, how else would you transfer pressure through the ball bearing oriface?

Hmmm?<G>

Thanks Rad for catching my mistake, back to the editor.

GZ

Click to expand...

Fluid flowed through the vent regardless of the position of the sealing ring the springs tension. They are there to position that ring so that an even, constant pressure is applied against it. I would imagine the pivoting of the cap assembly necessitated this, as a solid ring would eventually distort and refuse to seal. As it is only a vent, with minimal flow needs, the route need not be large. In fact, there appear to be multiple paths to the vent hole, the well is slotted to allow flow regardless of the plate position. The check ball doesn't depend on anything but gravity for it to allow flow-it sits in the well lying on the plate that covers it, doing nothing until a tipover allows fuel to push it against the orifice, stopping flow. The flow through the small opening at the latch base (the actual lock tab housing) is plenty . I have not examined any of the aux cells folks use, but it would seem that they should have a vent system of their own for the system to work properly-if they depend on the tank system, then the same path used for fuel flow would also have to vent the aux tank, I don't think that would be a good plan. But then, as I said, I haven't checked one out.

Note- I should emphasize one thing-once any influence has seated that check ball against the vent orifice, nothing is going to dislodge it until the internal pressure of the tank is relieved. Once in place, it ain't moving. Those who have experienced tank problems would probably be best off removing it altogether. It is the only mechanical block in the entire venting system,at least on 49 state bikes.

About the little ball. I heard from an expert that the ball is only there to stop fuel flow if the bike ever lands perfectly upside down.

Yea, that'll happen. :yahoo:

Rad, I'm a bit confused by your last description about getting fluid through certain passages, but I trust you know what you're doing.

That wouldn't happen on my cap. Go figure.

GZ

I can hardly wait to get my new cap in so I can tear the old one apart. In the meantime, I need my bike for transportation.. so this project will have to wait a bit.

It's hard for me to comprehend all that ya'll are typing without seeing the parts up close and personal.

See? This is just another example of where my simple-assed, agrigucultural-based Harley Davidson is truly superior. The cap is stinking cap, just like the one your old 1964 Malibu used to have. No venting, no springs, no pressure relief balls, and CHEAP!

beeroux said:

About the little ball. I heard from an expert that the ball is only there to stop fuel flow if the bike ever lands perfectly upside down.
Yea, that'll happen. :yahoo:

Rad, I'm a bit confused by your last description about getting fluid through certain passages, but I trust you know what you're doing.

That wouldn't happen on my cap. Go figure.

GZ

Click to expand...

I can only guess then that something is blocking the passage somewhere in your cap assembly. IIRC, you do have quite a few more miles on than I do. I checked several times, both brake cleaner and compressed air flowed easily when shot into the small hole at the rear of the cap. It also came out from multiple areas, not just one, which led me to believe the cap allows entry into the check ball orifice from many small openings in the part of the cap exposed to tank pressure once closed. Once closed, the ring rises against the 4 springs, exposing a gap of about 1/8", I think this is the main channel for tank venting through the check ball orifice. The hole you drilled was a good plan, but the real problem I think is downstream on your cap assembly. You others, a quick check to see that the ball is indeed free is to remove the cap and just shake up and down-you can hear it rattle. If it doesn't, disassemble and find out why. Also, using brake cleaner and a wand/nozzle, spray the cleaner into the back hole on the cap. The cleaner should flow out from around the seal ring etc.

radman said:

I checked several times, both brake cleaner and compressed air flowed easily when shot into the small hole at the rear of the cap. It also came out from multiple areas, not just one, which led me to believe the cap allows entry into the check ball orifice from many small openings in the part of the cap exposed to tank pressure once closed. Once closed, the ring rises against the 4 springs, exposing a gap of about 1/8", I think this is the main channel for tank venting through the check ball orifice.

Click to expand...

This is how my gas cap seems to be operating. :huh:

Also, don't forget to trim the vent hose under the bike to prevent serious crud build-up in the gas cap area.

My guess with the venting issue of the cell is caused by excessive heat and expansion of air and gas in the main tank. The vent in the gas cap is not as efficient as the vent in the cell (blocked, dirty, too small, whatever), so when rapid air/fuel expansion occurs, fuel just heads to the back of the bike via the path of least resistance.

Since the Tanji is low lying cell, maybe back flow could be a bigger issue in this situation?