I am pretty sure my Charcoal canister is Clogged!

[Gpaw44]

I am thinking I am getting a vapor lock caused by my 40 year old fuel canister being clogged.
It is a 1986 GMC/Chevy truck, 305 V8 with a carburetor. On the fuel pump there is an inlet for the line coming from the tank and an outlet for the metal line going to the carb. The third outlet on the pump I'm asuming it is the vent, where a rubber hose connects it to the charcoal canister. I'm I right?
My truck would not start with a new rebuilt carb till I bleed the metal line coming from the pump to the carb. After bleeding the line the truck was runnin
great! Today it was cool and after driving for about 30 minutes it would not start again. The engine was not that hot to cause a vapor lock. I have never had a vapor lock before, It was getting dark so could not see into the carb to see gas squirting. I will look in the morning but I think there is no gas in the line from the pump and in the carb and I will have to bleed the line once again. Yes the tank is full and the fuel tank and filter are new along with a newly rebuilt carburetor. Has anyone else had a vapor lock caused by a clogged canister. Thanks for your help!

 

[Ricko1966]

I am thinking I am getting a vapor lock caused by my 40 year old fuel canister being clogged.
It is a 1986 GMC/Chevy truck, 305 V8 with a carburetor. On the fuel pump there is an inlet for the line coming from the tank and an outlet for the metal line going to the carb. The third outlet on the pump I'm asuming it is the vent, where a rubber hose connects it to the charcoal canister. I'm I right?
My truck would not start with a new rebuilt carb till I bleed the metal line coming from the pump to the carb. After bleeding the line the truck was runnin
great! Today it was cool and after driving for about 30 minutes it would not start again. The engine was not that hot to cause a vapor lock. I have never had a vapor lock before, It was getting dark so could not see into the carb to see gas squirting. I will look in the morning but I think there is no gas in the line from the pump and in the carb and I will have to bleed the line once again. Yes the tank is full and the fuel tank and filter are new along with a newly rebuilt carburetor. Has anyone else had a vapor lock caused by a clogged canister. Thanks for your help!

The 3rd pump line is just a return to the tank,not to the vapor canister. The vapor canister does vent your tank,if its not venting you can't pull fuel,but easy enough to diagnose. Run with the gas cap off see if the problem is gone.I'd be more inclined to think you have a weak fuel pump.Because the vacuum would still be in the tank whether you cracked the fuel line or not. Another possibility is a leaky fuel hose,fuel line or tank switch allowing the pump to suck air,theyll suck air but not leak fuel,theres no positive pressure on the inlet side of the pump only negative pressure* vacuum)
Check your pump pressure. Also on a 3 line pump,quadrajet,if you have a tiny leak in the needle and seat and the wrong fuel filter in the carb inlet or no fuel filter in the carb inlet. The carb will bleed all the fuel in it back to the tank through the vent line so you are trying to start with an empty carb and empty line to the carb.

 

[Gpaw44]

Thank you Ricko1966 for your response. This morning I will remove the gas cap as you suggested. The reason I suspect the Charcoal canister, about 6 weeks ago my truck stoped running an has not been reliable since. All the fuel system has be changed. New tank, new sendiing unit, new hoses, new fuel pump, new filter after the pump, and new rebuilt carb. I even eliminate the 2 tank switching valve by connecting the new hoses from the tank directly to the metal fuel lines that go to the fuel pump. The truck might run great for a while and then it will die or not start!
WHEN I removed the carb to have it rebuilt there is a larger hose that is connected to the front of the carb near the top that goes directly to the C.C. When I pulled that hose there was gas in that hose. The person that rebuilt the carb suggested that I cap that at the carb and leave the line going to the C.C. open. I did cap the metal stub leaving the top of the carb but I did plug the hose going to the C.C. thinking gas might leak out there. This morning along with removing the tank cap I will uncap that hose.

How do you test the fuel pump when the there is a metal line coming from the fuel pump and goes directly into the carb? Thanks

 

[PrairieDrifter]

How do you test the fuel pump when the there is a metal line coming from the fuel pump and goes directly into the carb? Thanks

Remove the line from the carb and get a rubber hose and shove it in a bottle. I think it's like 5-6 pumps should fill a 16 ounce bottle.

Parts store fuel pumps are complete junk these days. I went through 6 of em.

I would recommend the Edelbrock mechanical pumps, they seem to work good, only thing is you have to modify the pump to carb line.

 

[Ricko1966]

Thank you Ricko1966 for your response. This morning I will remove the gas cap as you suggested. The reason I suspect the Charcoal canister, about 6 weeks ago my truck stoped running an has not been reliable since. All the fuel system has be changed. New tank, new sendiing unit, new hoses, new fuel pump, new filter after the pump, and new rebuilt carb. I even eliminate the 2 tank switching valve by connecting the new hoses from the tank directly to the metal fuel lines that go to the fuel pump. The truck might run great for a while and then it will die or not start!
WHEN I removed the carb to have it rebuilt there is a larger hose that is connected to the front of the carb near the top that goes directly to the C.C. When I pulled that hose there was gas in that hose. The person that rebuilt the carb suggested that I cap that at the carb and leave the line going to the C.C. open. I did cap the metal stub leaving the top of the carb but I did plug the hose going to the C.C. thinking gas might leak out there. This morning along with removing the tank cap I will uncap that hose.

How do you test the fuel pump when the there is a metal line coming from the fuel pump and goes directly into the carb? Thanks

That hose is the bowl vent,and gasoline will ruin a charcoal cannister. If you have fuel coming it out of that I suspect a bad float,a leaky needle and seat or in correct float level.I wouldn't plug a bowl vent.

 

[Broken85]

Thank you Ricko1966 for your response. This morning I will remove the gas cap as you suggested. The reason I suspect the Charcoal canister, about 6 weeks ago my truck stoped running an has not been reliable since. All the fuel system has be changed. New tank, new sendiing unit, new hoses, new fuel pump, new filter after the pump, and new rebuilt carb. I even eliminate the 2 tank switching valve by connecting the new hoses from the tank directly to the metal fuel lines that go to the fuel pump. The truck might run great for a while and then it will die or not start!
WHEN I removed the carb to have it rebuilt there is a larger hose that is connected to the front of the carb near the top that goes directly to the C.C. When I pulled that hose there was gas in that hose. The person that rebuilt the carb suggested that I cap that at the carb and leave the line going to the C.C. open. I did cap the metal stub leaving the top of the carb but I did plug the hose going to the C.C. thinking gas might leak out there. This morning along with removing the tank cap I will uncap that hose.

How do you test the fuel pump when the there is a metal line coming from the fuel pump and goes directly into the carb? Thanks

You said you eliminated the switching valve and hooked the tanks directly to the fuel line??? I am curious to hear how you did this, as the switch valve also switches the return line to the correct tank, not to mention switching what tank you draw from.

 

[PrairieDrifter]

You said you eliminated the switching valve and hooked the tanks directly to the fuel line??? I am curious to hear how you did this, as the switch valve also switches the return line to the correct tank, not to mention switching what tank you draw from.

Not all of them had returns, even on dual tank trucks.

Just connect one tank supply to the main supply, valve is bypassed to confirm it's not the issue while pulling directly from the tank. Perfectly normal for testing.

It should return fuel to one of tanks anyways. Or you could connect the return hoses together as well.