How to fix a fuel cap vapor lock

[Engel6264]

Hello
Met this couple here in Maggie and they have a 99 Goldwing Trike.
They have a problem with vapor lock and seem to think it has to do with cap!
It gets to passed half a tank and starts having problem with fuel , almost feels like it can't get to where it needs to go. When they get to half tank he fills up and has alot of pressure release when cap opens.
Any of you dealt with this kind of issue??

Angel

[DenverWinger]

The most recommended fix is to soak the fuel cap in Seafoam 24 hrs.....

[MikeB]

Hello
Met this couple here in Maggie and they have a 99 Goldwing Trike.
They have a problem with vapor lock and seem to think it has to do with cap!
It gets to passed half a tank and starts having problem with fuel , almost feels like it can't get to where it needs to go. When they get to half tank he fills up and has alot of pressure release when cap opens.
Any of you dealt with this kind of issue??

Angel

It sounds like a fuel delivery problem. But wouldn't pressure in the tank only add to the ability to deliver fuel to the carburetors? I would think that built up vacuum in the tank would cause a lack of fuel delivery, not pressure.

Is the fuel pump not delivering fuel adequately? Or maybe the fuel auto-shut-off valve is compromised in some way.

[Rambozo]

A lot of people hear air rushing when they open the cap and think pressure, but fail to notice which way the air is going.

[LAB3]

When it happened on mine I took a small drill bit and put a hole in it, hasn't given me any problem since!

[WingAdmin]

Pretty common problem. There is a two-way valve in the gas cap that opens when too much pressure (from heat) builds up, or when too much vacuum (as fuel is used up) builds up. It lets air in or out as required when the pressure exceeds a given amount. Over time, fuel residue can clog the valve and cause it to stick shut, which means the vacuum builds up to the point where the fuel pump can't overcome it, and the engine quits from fuel starvation. Opening the fuel cap lets air rush in and fixes the problem - temporarily.

Drilling a hole in the cap will fix it, but it also means your tank is now open to the environment for every tiny little change in temperature, and is constantly sucking in air and pushing it back out. You'll smell fuel fumes, and moisture will condense into water inside the tank, rusting the tank from the inside.

The best solution is already posted - buy a few cans of Seafoam, pour into a small bucket and soak the gas cap in it overnight. If that doesn't fix it, then sometimes boiling the gas cap in water can do it - and if that does do it, you're looking at a new gas cap.

Incidentally, the Seafoam is still useful after using it for this - as long as it's clean with no debris, pour it into your lawnmower or whatever to clean out its fuel system!

[ct1500]

With a vacuum in a tank you literally have to pull the gas cap up to break the vacuum seal which likely is not the case in your situation.

[Dirtrack650]

Berrymans B-12 is much cheaper than Seafoam and is a more aggressive cleaner well suited for things like gas tank caps.

All of my bikes I ride are salvage or barn finds. Dropping the gas caps in the ultrasonic cleaner loaded with WD-40 is my preferred method.

[boomerang]

Don't forget that a common cause of fuel starvation is a weak fuel pump. As the level in the tank drops more effort is required to pump the fuel. The lower the level, the worse the erratic throttle responses, particularly under heavy load. There are great forums on economical fuel pump replacement that were a great help to me.