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2001 Kawasaki Vulcan 750
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Discussion Starter · #1 · (Edited)
Hi Vulcaners, love this bike so much, Had a nice cruise yesterday and today down Old Monterey Rd, and to Los Gatos/Saratoga.

I'm asking for more brain power to add what little I've got left, on this topic.

I filled gas tank for first time today, just below the filler neck. A few stop lights later, I saw gas trails dribbling down the front and back of the tank, and on the cap itself. Just for the record, the cap has been fully disassembled and cleaned and carefully re-assembled and the o-rings treated lightly with o-ring grease.

Rode long enough to bring the gas level down so it was just barely above the tank backbone, several inches below the filler neck. It still weeps gas down towards the seat. Photos attached.

When the cap is closed and the bike parked and off, I can hear air/vapor noises thru the cap. Don't know what they are.

Anyway, I did read a few postings on here, I don't see how the o-rings under the cap mounting screws would let out this quantity of gas (the tracks are pretty substantial)?

I don't know if a new gas cap flap gasket would help, it seems to seal ok, but can't be sure?

And finally, there is that hole in the tank itself under the rear of the gas cap. This is something to do with vapors and the canister. Could that be it? The vapor canister is spitting gas back up and out the cap there? The two vapor hoses from the back of the California tank are connected to where they should be.

Thanks for your thoughts, ride safe (I need to tell this old guy that every time I go out, its been long time since I've been on a bike...)

53016
53017
53019
 

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It's normal to get a bit of a whistle or squeal from the cap, especially in the sun.

The nipple in the center looks like it might be pushed to one side.
 

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2001 Kawasaki Vulcan 750
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Discussion Starter · #3 ·
It's normal to get a bit of a whistle or squeal from the cap, especially in the sun.

The nipple in the center looks like it might be pushed to one side.
There ain't no nipples on that thing. Should there be some rubber thing in that vent hole?
 

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There ain't no nipples on that thing. Should there be some rubber thing in that vent hole?
Yes, there should be a rubber tit sticking up to press over the corresponding hole in the gas cap.

If that's just an empty hole between the mounting screws, you're missing a piece.
 

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Discussion Starter · #5 ·
Yes, there should be a rubber tit sticking up to press over the corresponding hole in the gas cap.

If that's just an empty hole between the mounting screws, you're missing a piece.
Dam! All this talk of tits and nipples.. haha.. So its bad if the Vulcan is missing those! Thanks mucho, I will hit up the stealership and pay him his $6 for that thing and wait two weeks to get it, and that should do it fingers crossed.
 

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With the right size vacuum hose cut to the right length, you can probably make one.

Edit: Viewing your pics on the pc now, it's definitely missing.
 

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Discussion Starter · #8 ·
With the right size vacuum hose cut to the right length, you can probably make one.
"You just keep thinkin' Butch, that's what you're good at!" Thx for the ideas, i never would have thunk of it myself, now I can try that out tomorrow.
 

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"You just keep thinkin' Butch, that's what you're good at!" Thx for the ideas, i never would have thunk of it myself, now I can try that out tomorrow.
There used to be a great quote from that movie, but I think they cut it out for tv. I can't even repeat it on here.

None on ebay and bikebandit says 1-2 weeks shipping but wants you to login for price and availability.

If you can make the hose press snug against the gas cap, it should work.
 

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Discussion Starter · #10 · (Edited)
There used to be a great quote from that movie, but I think they cut it out for tv. I can't even repeat it on here.

None on ebay and bikebandit says 1-2 weeks shipping but wants you to login for price and availability.

If you can make the hose press snug against the gas cap, it should work.
Thanks Spockster. I got the gas tank vent hole seal, it was used but he still charged me $6 what the heck they need to make a living too, right?
53048

I put it in from the top of the cap, but it still leak badly, even though the tank is only 1/2 full.

I removed the cap and pressed it up into the cap seating hole from the bottom, and this obviously would seal the gas tank vent hole better, as the lower seal area would be pressed over the gas tank vent hole.

UPDATE: It still leaks, just as as badly. I will have to eliminate variables, so I will just cover over the gas tank vent hole with tape so no gas could possible come up from there.

Then, if it still leaks, I know that the rubber sealing ring built into the cap itself is not holding, and I can install a new rubber seal up there.
 

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Discussion Starter · #11 · (Edited)
Thanks Spockster. I got the gas tank vent hole seal, it was used but he still charged me $6 what the heck they need to make a living too, right?
View attachment 53048
I put it in from the top of the cap, but it still leak badly, even though the tank is only 1/2 full.

I removed the cap and pressed it up into the cap seating hole from the bottom, and this obviously would seal the gas tank vent hole better, as the lower seal area would be pressed over the gas tank vent hole.

UPDATE: It still leaks, although not as badly. I will have to eliminate variables, so I will just cover over the gas tank vent hole with tape so no gas could possible come up from there.

Then, if it still leaks, I know that the rubber sealing ring built into the cap itself is not holding, and I can install a new rubber seal up there.
UPDATE: NOT GOOD.

It is worse with the vapor hole in the gas tank taped over.

On today's fill up, it actually was as if the gas was under pressure.
It shoots up and out of the top of the cap where the key fits in, surprisingly.
It also streams out of the sides of the filler cap and all down the tank to the seat, very badly.

I thought the rubber filler hole seal or little vapor seal would be the cause, but those seem to look good.

And when I park the bike, the pressure is just wheezing out of the cap.

I can't even ride like this anymore, so much gas comes out I'm worried it will leak to the engine and catch on fire.

So,
1) Would getting a new cap solve this?

2) Is my vapor management system run amok? Those two CA-only hoses at the bottom back of the tank, one for vapor out and one for liquid return from the return/separator valve?

All hoses AFAIK are connected properly.

I would like to figure a way to test and locate the problem before I go buying a new gas cap. This is my highest priority thing to tackle now.

53067
 

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I was thinking maybe it's the gas cap. Make sure the charcoal canister isn't full of gas, just in case.

The tape over part of the vent will probably cause more pressure and might cause a different leak.

The vapor is supposed to flow through the cap, through the rubber nipple, and then to the charcoal canister. Unless I've misread the diagram.

The vacuum line to the separator is good?
 

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Discussion Starter · #13 · (Edited)
I was thinking maybe it's the gas cap. Make sure the charcoal canister isn't full of gas, just in case.

The tape over part of the vent will probably cause more pressure and might cause a different leak.

The vapor is supposed to flow through the cap, through the rubber nipple, and then to the charcoal canister. Unless I've misread the diagram.

The vacuum line to the separator is good?
Appreciate some thoughts. I'm kinda depressed over this but will get back at it tomorrow. I already took off the tape over the tank vent hole to let all that flow.

I was researching the Vulcan forums. One post said there is a tube that runs through the tank from that vapor vent hole. If so, then that is what is causing havoc, because I used a pressure wash and blasted the whole insides of my tank to knock off the rust scaling and clear out that gunked up mess from 8 years sitting.

The vapor diagram I posted in #11 shows two flow lines. I think one is for collecting the vapors and line #8 is the return line which the separator pump returns the liquid gas back that was extracted from the vapor. Are they physical lines inside the tank that I could have screwed up?

Hope that is not the case.

This gives me the idea of disconnecting that stinkin' return line from the tank altogether for now, and I could attach a "catch can" to it to collect any liquid. Or maybe the vapor out / gas return lines are somehow switched. I just want to ride, this is bumming me out some.
 

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One thought comes to mind, and if you mentioned this I apologize for being redundant. I clearly remember reading on the forum somewhere that you can only fill the California models a little over 3/4 tank of gas. This was one of the reasons people were stripping these systems out of the bike.
 

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With the cap open, try blowing air up through tank from the port that connects to the charcoal canister. I believe air should come through the rubber nipple at the cap.

Maybe also try this with the cap closed.
 

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One thought comes to mind, and if you mentioned this I apologize for being redundant. I clearly remember reading on the forum somewhere that you can only fill the California models a little over 3/4 tank of gas. This was one of the reasons people were stripping these systems out of the bike.
Haven't heard this, but it could be a workaround for the Cali bikes.

Bad news because she doesn't carry enough gas to start with. Normal fill-up is to the bottom of the neck without touching it. It's easy to get gas into the canister by filling completely to the brim, even on your car.
 

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Yeah I wish the tank was just a bit bigger, I’m searching for that thread for sanity. I’ll link it if I can find it. Supposedly there was a sticker warning of overfilling the bike on the tanks.
 

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Ok here is one of the threads, it’s not a super technical thread, more like bickering from a member that if you’re familiar with him you say “oh that guy” when you read his posts. But there are a few mentions about the caution stickers to not overfill the CA models. Again I’m not sure if this directly helps your issue, but as an engineer sometimes we say “worth a shot”

 

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Discussion Starter · #19 · (Edited)
Ok here is one of the threads, it’s not a super technical thread, more like bickering from a member that if you’re familiar with him you say “oh that guy” when you read his posts. But there are a few mentions about the caution stickers to not overfill the CA models. Again I’m not sure if this directly helps your issue, but as an engineer sometimes we say “worth a shot”

Tried it and haven't found the solution yet.

I thought it would be caused by incorrect hose routing from the return/separator pump, or the charcoal canister full of gas or some such.

So, using the diagram in post #11, and the one I am attaching here, I very carefully checked hose connections. They were all routed correctly and I double and tripled checked that.

I took out the return/separator pump and the canister, and all the lines were clear. No gas in the canister. There was a small amount of gas in the separator line that is the return to the gas tank - just as it is supposed to be if it extracts liquid gas from the input vapor line.
53072

I blew into the vapor out line and the gas return line on the gas tank, and got clear passage just as it should. The vapor out comes from the hole in top of the tank under rear of the fuel tank latch. The gas return goes somewhere up in the top of the tank, it did not blow bubbles, so it is above the fuel level itself.

The separator pump has two inputs and two outputs. At the top is the inlet of gas vapor from the tank, and the outlet of gas vapor to the charcoal canister. At the back of the barrel is the output of gas liquid back to the tank. At the bottom is the input from the vacuum air switch, which makes the whole thing work.

I could blow into or draw air out of the inlets and outlets and they seemed fine except I could not get any movement from the bottom vacuum air switch input. I haven't yet found any write-up on how to bench test the separator pump.

So to simplify, I eliminated the complete vapor management system.

At the back of the gas tank, i took a length of rubber hose (7/32" I.D.) and just connected the vapor out nozzle to the gas return nozzle.

I smugly hit the road. Rode to the post office all was good.

Then! Came out of post office and saw a drop coming out of filler cap. Started the bike, and it poured out again. <Insert curse words here>.

When I got home, I heard the cap whistling and wheezing. Opened it for a while, then closed it. After a few seconds the air sounds started again. Five minutes later it was still doing it.

So the cause is from the connections at the petcock! It kinda makes sense because the petcock pulls a vacuum and sucks the gas out into the carburetor float bowls.

So I yanked off the seat, and pulled off the gas return end of the hose that I had used to inter-connect the vapor/gas return lines on the back of the gas tank. One drop of gas, and the air whistling stopped instantly.

Put the hose back on, and amazingly it started wheezing again. Pulled off the vapor out end of my inter-connecting hose and the wheezing stopped instantly.

Ok, so I have to come up with a plan of action from here.

I have some good clues, and have to use them to solve this mystery. Your thoughts are more than welcomed.
 

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The whistling occurs on bikes without Cali emissions also.

Vacuum on the petcock opens the diaphragm, then the gas flows by gravity.

I'm guessing it probably needs a gas cap.
 
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