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"Vapor Lock"

Old 01-05-2013, 04:41 PM
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"Vapor Lock"

Has anyone else had issues with the VTR stumbling and dying in the rain? I know its not electrical because I have carried a spare key and popped open the gas cap (while still rolling!) and it clears itself and runs fine until it happens again. Long ago I remove the plastic T fitting that I believe connected the fuel tank breather hose to another hose, with the single hose from the T running down (which was purposely kinked in such a way to create P-trap in the hose) to behind the chin fairing along with the coolant recovery tank and fuel tank overflow hoses. I tried running the fuel tank breather hose directly (without the P-trap) to the chin fairing via various routes; and now have it run down to between the alternator cover and clutch slave cylinder to a level below the bottom of the engine (and even cut the end of the hose at a bias with the hole to the rear) in an attempt to create negative pressure on the hose as it runs in the airstream. But even in a moderate rain, the dam fuel tank "vapor locks" until I open the gas cap!!!???

Helpful input with this problem will be much appreciated!
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Old 01-05-2013, 05:02 PM
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It is usually caused by a low spot in the vent line which allows water to get trapped in the line.

On mine I just made sure the line was straight with no place for water to get trapped and the issue went away.
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Old 01-05-2013, 05:32 PM
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Originally Posted by 8541Hawk View Post
It is usually caused by a low spot in the vent line which allows water to get trapped in the line.

On mine I just made sure the line was straight with no place for water to get trapped and the issue went away.
Mike, I have the fuel tank vent hose as straight, direct and short as possible but it still gives me fits in the rain??
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Old 01-05-2013, 05:36 PM
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Well at that point I would first check the line and make sure nothing is stuck in it (try blowing through it) or remove the line completely and see if the problem still happens.
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Old 01-05-2013, 06:22 PM
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Check that the front plug isn't getting drowned in the rain - as there is a small hole that should allow water to drain from the deep recess and if that gets blocked it can cause problems - as I found out on one very wet ride it causes symptoms very similar to PVLIR.

I've also applied silicone grease around the rubber seal on the spark plug cap to keep it water tight.

Last edited by Wicky; 01-05-2013 at 06:25 PM.
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Old 01-05-2013, 06:35 PM
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Originally Posted by Wicky View Post
Check that the front plug isn't getting drowned in the rain - as there is a small hole that should allow water to drain from the deep recess and if that gets blocked it can cause problems - as I found out on one very wet ride it causes symptoms very similar to PVLIR.

I've also applied silicone grease around the rubber seal on the spark plug cap to keep it water tight.
Don't think this is the issue in this case as the problem clears up when he opens the gas cap.
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Old 01-06-2013, 09:25 AM
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Originally Posted by 8541Hawk View Post
or remove the line completely and see if the problem still happens.
I've thought about trying that but with a short hose kept out of the wind. Can the vent line leak gas, as there is no check valve?

Originally Posted by 8541Hawk View Post
Well at that point I would first check the line and make sure nothing is stuck in it (try blowing through it) or remove the line completely and see if the problem still happens.
Did that 1st thing with compressed air with the gas cap open; it is clear and flows well.

Originally Posted by VTRsurfer View Post
I had that problem once. Try cutting the bottom of the vent hose at an angle, facing the rear of the bike. That worked for me.
If you review my post, I tried that too.
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Old 01-06-2013, 10:14 AM
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Originally Posted by 8541Hawk View Post
Don't think this is the issue in this case as the problem clears up when he opens the gas cap.
skokievtr asked "Has anyone else had issues with the VTR stumbling and dying in the rain?"

My problem seemed to clear up after a while while I stopped only to keep reoccuring a few miles down the road in heavy rain. So IMHO something to consider along with all the other vaild answers offered. But if you don't think its worth inspecting in a minute or two to rule out then the OP can choose to ignore my suggestion offered in good faith and from experience.
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Old 01-06-2013, 10:23 AM
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Originally Posted by Wicky View Post
skokievtr asked "Has anyone else had issues with the VTR stumbling and dying in the rain?"

My problem seemed to clear up after a while while I stopped only to keep reoccuring a few miles down the road in heavy rain. So IMHO something to consider along with all the other vaild answers offered. But if you don't think its worth inspecting in a minute or two to rule out then the OP can choose to ignore my suggestion offered in good faith and from experience.
No disrespect meat but he also started that he has carried an extra key and opened the tank while the bike was running and the issue cleared up which would make the issue sound vacuum related not an ignition problem.

So while the problem could be from the cause you have listed I would not think it is the likely problem.
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Old 01-06-2013, 10:29 AM
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Originally Posted by skokievtr View Post
I've thought about trying that but with a short hose kept out of the wind. Can the vent line leak gas, as there is no check valve?
There is no check valve and I have worked on a few of these bikes where the lines have been removed completely with no issues, well other than the vent and\or overflow dumping fuel on to the top of the airbox.

It does sound like a strange problem.
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Old 01-06-2013, 05:12 PM
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Skokie, I have only ever had that problem when I filled the tank too high, and not in rain, but it could be related. If you cap is not venting when wet then that could kinda be the same issue.

I had that issue on a race bike & checking all the gas cap venting (disassemble and clean/blow out) solved it.

It seems obvious its liquid related. If you are sure the vent hose is perfectly clear try looking upstream. Like the drain hole that allows overfilled gas to drain out to the ground.

Just some lateral thinking two cents.
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Old 01-06-2013, 07:15 PM
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Try putting another tee in much lower in the vent tube, like behind the lower cowl.
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Old 01-08-2013, 11:50 AM
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Originally Posted by 8541Hawk View Post
There is no check valve and I have worked on a few of these bikes where the lines have been removed completely with no issues, well other than the vent and\or overflow dumping fuel on to the top of the airbox.

It does sound like a strange problem.
I know there is no check valve but I recently bought a fuel cell check valve on sale at Cycle Gear for $5 (TRACKSIDE Parts & Accessories - Gas Cap Vent Tube with Check Valve - Cycle Gear I plan to connect to a shorter vent hose under the tank.

Originally Posted by smokinjoe73 View Post
Skokie, I have only ever had that problem when I filled the tank too high, and not in rain, but it could be related. If you cap is not venting when wet then that could kinda be the same issue.

I had that issue on a race bike & checking all the gas cap venting (disassemble and clean/blow out) solved it.

It seems obvious its liquid related. If you are sure the vent hose is perfectly clear try looking upstream. Like the drain hole that allows overfilled gas to drain out to the ground.

Just some lateral thinking two cents.
I believe the gas cap does not vent (which is why there is the tank vent). I've thought about buying a venting cap (i.e., Honda Rapid Lock Tank Cap Silver) but they are a bit pricy at $135 if not also very cool.

Originally Posted by Hawkrider View Post
Try putting another tee in much lower in the vent tube, like behind the lower cowl.
Greg, see above and what would adding a T do (there is none now), and where should it go?
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Old 01-08-2013, 02:44 PM
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I am pretty sure the tank vents...BUT, is that drain hole on the filler neck rim clear? That is venting. If you over flow the gas tank the surplus should go down that hose(and onto the ground). If it is clogged then it willl cause vapor lock. Blockage could also cause water to build up there & seal off venting.
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Old 01-08-2013, 02:58 PM
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Originally Posted by smokinjoe73 View Post
I am pretty sure the tank vents...BUT, is that drain hole on the filler neck rim clear? That is venting. If you over flow the gas tank the surplus should go down that hose(and onto the ground). If it is clogged then it willl cause vapor lock. Blockage could also cause water to build up there & seal off venting.
The gas cap does not vent. There are 2 hoses from the bottom of the tank. One is for the filler overflow "ring" drain, the other is the tank vent. The tank vent hose connects to the smaller "nipple" under the tank. This nipple is the end of a steel tube that extends up to the underside of the hollow "doughnut" that is below the overflow drain ring.

If you read my prior posts more carefully, I've checked the vent hose & tube for blockages. Next up is a shorter hose, possibly connected to a check valve. I may also try installing my spare gas cap assembly (which is on my modified OE fuel tank I enlarged to 5.2 gallons).

The problem is simulating riding in the rain (at speed) to verify if the "fixes" worked! Any suggestions for that guys?
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Old 01-08-2013, 04:25 PM
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Originally Posted by skokievtr View Post
Greg, see above and what would adding a T do (there is none now), and where should it go?
It would provide an additional vent path which would prevent sucking water up into the line. I would put it a couple inches above the end, where you can't see it.
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Old 01-08-2013, 05:08 PM
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Originally Posted by Hawkrider View Post
It would provide an additional vent path which would prevent sucking water up into the line. I would put it a couple inches above the end, where you can't see it.
OK, I get it. I just don't see why the vent hose can't be short and just be left up under the tank. Could it leak?

However, the check valve (see prior post) I have must be pointed up up, so I could attach a short piece of hose to the vent nipple (which points down) under the tank, then connect a T to it. From the bottom of the T a long hose would extend down to the chin fairing as OEM or somewhere more directly downward below the engine), and from the T's side-spigot a short piece of hose would connect to the check valve; with the check valve secured to the petcock so it was vertical. This way on the odd chance the vent did drip gasoline, it would drain to the ground and the check valve would prevent gas from spilling up under the tank.
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