Fuel Tank Vapor Canister 521

[brodster]

Okay, I have spent the last hour looking at posts regarding this, and I am left with two questions:

 

1. Are there any perforamce negatives to removing that vapor canister thing on the wheel well?

 

2. If I were to disconnect all of that and chose to vent the fuel tank, what is the proper method?

 

I normally would really care about pulling it, but I recently spent some time troubleshooting an interesting problem. Basically, after running the truck (immdiately after buying it) the engine started choking as I would climb hills or do anything but an idle. Anytime I demanded more it would crap out. It would progressively get worse until it would even die at idle.

 

I went through all the typical checks: air leaks, fuel filter, etc. Replaced all of the rubber hoses forward of the hard fuel line coming into the engine bay. Replaced the fuel filter.

 

I discovered that after the truck rested for a significant amount of time, more than about 30 minutes it would run like a champ again. Then it would symptoms after 30 minutes.

 

To make a long story short, I decided to see if there was excessive vaccuum in the fuel tank. I figured that little pump couldn't really perform under huge vaccuum. When the symtoms reappeared, I removed the gas cap. It was somewhat hard to twist. When the seal broke, WHOOSH. Huge inrush of air. All symptoms dissappeared. Now I just have to remove my gas cap every half an hour of steady driving. :D

 

Anyways, not sure where the clog is. As I have read, I probably drop the tank and clean it out, replace all rubber hoses, etc. But that vapor canister seems to be completely unnecessary. I wondering if I could just vent the tank with sometype of filter or something to keep debris out.

 

Thanks!

[DanielC]

There is a valve in the engine compartment, Approximately between the carburetor, and the windshield washer bag, with three hoses attached to it. One hose goes to the engine crankcase, with a little pipe on the side of a bigger pipe below the manifolds. One hose goes to the underside of the air cleaner, and the third hose goes to the "cannister". The cannister is not a charcoal cannister. it is a vapor- liquid separator.

 

The gas tank is vented through the separator, by two hoses. One goes to the fuel filler neck, the other goes to the gas tank. There are three hoses connected to the separator.

 

Make sure the hoses between the separator are clear. Make sure the hose from the valve in the engine compartment to the separator are clear.

 

The valve allows air to flow from the clean side if the air cleaner, back to the tank.

[gene knight]

i am running a L18 in 521 and a weber 32/36 maunual choke carb and i am not planning to use extra vent tank

so is there a way to plumb up fuel system without it?

[DanielC]

An evaporative emission system is a good thing. It recycles the gas fumes back into the engine, where they are burned. Theoretically, you should get better gas mileage with it hooked up, than with out it.

[brodster]

There is a valve in the engine compartment, Approximately between the carburetor, and the windshield washer bag, with three hoses attached to it. One hose goes to the engine crankcase, with a little pipe on the side of a bigger pipe below the manifolds. One hose goes to the underside of the air cleaner, and the third hose goes to the "cannister". The cannister is not a charcoal cannister. it is a vapor- liquid separator.

 

The gas tank is vented through the separator, by two hoses. One goes to the fuel filler neck, the other goes to the gas tank. There are three hoses connected to the separator.

 

Make sure the hoses between the separator are clear. Make sure the hose from the valve in the engine compartment to the separator are clear.

 

The valve allows air to flow from the clean side if the air cleaner, back to the tank.

 

Sounds good. I will try to clear all the hoses before I start ripping stuff out. Thanks

[DanielC]

I found some more information on the valve. the three ports are labeled "A", "F", and "C"

"A" goes to the air cleaner.

"F" goes to the fuel tank cannister.

"C" goes to the engine crankcase.

 

This is how you test it.

Disconnect all the hoses.

 

Blow low pressure air into the "F" port. Air should come out of the "C" port.

Blowing into the "C" port should not have air coming out of the other two ports.

 

Blowing air into the "A" port should blow out of the "F" port and it can also have air blowing out of the "C" port. It is not necessary for air to come out of the "C" port, but it can.

 

Applying a slight vacuum (.4 inch HG) on the "F" port should cause air to be drawn through the "A" port.

 

The system uses the engine crankcase to store the fuel vapors. When the engine is not running, pressure from the gas pushes fuel vapor in the "F" port, and it goes out the valve to the "C" port, and into the engine crankcase.

 

When the engine is running, The engine crankcase develops a vacuum from the PCV valve, and the vapors in the crankcase go into the intake manifold. Fresh air can be drawn through the "A" port, and go into the fuel tank, and in some cases, also be drawn into the crankcase.

[brodster]

Excellent. Was going to test this weekend. That helps a lot