Disconnected line 1986 FJ1200

[chocker]

Hi,
I was working on the bike and when I removed the battery I noticed there was a disconnected tube or line on the lefthand side of the bike right where the end of the battery over flow tube was. The line must be about 1/4 inch. It has two clamps, one on either side of where it seems to be disconnected. There seems to be a metal tube within the line. It doesn't look like it is broken but just disconnected. It doesn't seem to affect anything but I would like to know what it is and reconnect it if necessary. I will try to post a picture as soon as possible.

Thanks,
Mark

[Arnie]

Mark,

It sounds like the fuel tank overflow tube.  Check to see if there is a bare nipple at the back of the tank.

Arnie

[chocker]

Mark,

It sounds like the fuel tank overflow tube.  Check to see if there is a bare nipple at the back of the tank.

Arnie

The overflow hose is transparent and it is still in place on the tank. This is a black hose running on the lefthand side and below the battery.

[56 CHEVY]

Could it be the battery vent hose?

On my 86 the fuel overflow tube was black and the battery vent hose was transparent. Possibly mixed up?

[chocker]

Could it be the battery vent hose?

On my 86 the fuel overflow tube was black and the battery vent hose was transparent. Possibly mixed up?

Actually I found it because the battery breather hose was touching it. It is running alongside the lefthand side of the bike.

[56 CHEVY]

 The only other hose that I can think of on that side, around that location, would be the vacuum line to the ignition box.

On mine there are no other hoses in that area.

[chocker]

The only other hose that I can think of on that side, around that location, would be the vacuum line to the ignition box.

On mine there are no other hoses in that area.

What exactly would it do if it is disconnected. I am able to start and run the bike. I see there maybe a little bit of backfire lately.

[56 CHEVY]

 If I understand correctly, it works like the vacuum advance can back when cars had distributors. At cruise or light load (high vacuum) the TCI unit will advance the timing an additional 10 to 15  degrees over the advance curve programmed in the unit. This helps fuel economy and throttle response. Heavy acceleration/load, (low vacuum) the unit will not provide the additional advance in order to prevent detonation.

The bike will start and run without it hooked up, but you will have a vacuum leak if the hose is not capped. That could cause a backfire?

[chocker]

If I understand correctly, it works like the vacuum advance can back when cars had distributors. At cruise or light load (high vacuum) the TCI unit will advance the timing an additional 10 to 15  degrees over the advance curve programmed in the unit. This helps fuel economy and throttle response. Heavy acceleration/load, (low vacuum) the unit will not provide the additional advance in order to prevent detonation.

The bike will start and run without it hooked up, but you will have a vacuum leak if the hose is not capped. That could cause a backfire?

Thanks for the help everyone. I will try to reconnect it and see what happens and if there is an issue I will disconnect and plug it so there is no leak.

Thanks,
Mark

[andyb]

Start the bike and stick your finger over the end of it.  That'll tell you right away if it's a vacuum line or not!  More likely it's just a drain/vent that's been routed someplace unusual.

[chocker]

Start the bike and stick your finger over the end of it.  That'll tell you right away if it's a vacuum line or not!  More likely it's just a drain/vent that's been routed someplace unusual.

It's wierd though. It has a clamp on either side of where it is disconnected and within the hose there seems to be a metal insert. It is clean where both ends meet. I will try block it when it is running to see for sure.

Mark

[fj11.5]

sounds like the vacume advance line, they have a plastic joiner in the middle    , 

[chocker]

sounds like the vacume advance line, they have a plastic joiner in the middle    , 

I was able to inspect it more clearly this morning and it is the vacuum advance. I see that it runs into the ignition box and I felt the air being pulled in. Should I plug the end that goes to the carburator.

[Mark Olson]

try to hook it back up to the advance unit.

[SlowOldGuy]

Do you have an aftermarket ignition?

The diaphragm in the ignition box may be blown out.  See if you can pull a vacuum on the ignition side before you plug it back in.

Also, I think the plastic "joint" you are referring to is a vacuum check valve.  It's purpose is to prevent an intake backfire from rupturing the vacuum diaphragm in the ignition box (it isn't always successful).

If the ignition won't hold a vacuum, plug the line going to the carb to stop the vacuum leak.

DavidR.