Fuel Vent lines

[RMEVET]

Good morning -

I have a 1962 M151. The previous owner cut the forward most vent line on the fuel tank.

I believe (might be wrong) this might be the culprit to what’s causing the engine to shut off after about 5-10 mins of driving (not idling), vapor lock? After the engine cools down a bit, it fires up and starts the entire process all over again.

The line runs from the carb, to the air filter, through firewall to the very front of the fuel tank.

Questions, can I bridge the cut out piece with rubber tubing?

Kirk

[rickf]

Welcome Kirk. There are no vent lines that go from the carburetor to the tank or from the carburetor to the air cleaner. So someone has done some modification on there. Now, with that said, there is a line from the tank to the air cleaner. Two things you need to check before getting into the vent lines since it sounds like the vent line that needs to be there is actually there. Did you check the gas cap to see if it is the right cap for the early style tank? Most will have a valve inside the cap that can be turned 90 degrees to open the vent or close the vent for fording. Make sure it is open. Late emissions tanks used a cap with no vent. Also check the fuel filter to make sure it is not clogged. Since this is a straight 151 it should have the electric pump in the tank. If you take the fuel line off of the carb and hold it in a can and crank the engine with the switch off you will make the pump run while cranking. See if you get a strong flow of gas from the line. If you do then you need to check the filter. I am assuming this has all the factory equipment on it, If the filter is screwed directly into the carb body then you have an issue, let me know and we will discuss that further. Does this have the Zenith or Holley carb?

[Hambone]

You could pull the fuel line when it shuts down and make sure it is getting fuel, fuel problems don't fix their self after 10 mins. The coil will act like that also, hope it's fuel but don't rule out the coil if you're getting fuel, can you see rust in the tank?

[rickf]

You can also loosen the gas cap slowly and listen for air to suck in when it shuts down. If you hear that then there was a vacuum in the tank which means no vent. Wrong cap or valve set wrong or valve not working.

[RMEVET]

Thank you, everyone! I truly appreciate the help.

CORRECTION - the line runs from fuel pump, bypasses the top of the Zenith carb (not connected to it), to air filter, the line then runs along passenger side fender well to the firewall then down into the drivers side along the other fuel lines to the front of the fuel tank.

I’ve rebuilt the carb, changed out the fuel filter, engine idles fine well up to operating temps, take it for a drive, and it will loose power, and shut down. Cool down and start over, or tow it home.

vent line.jpeg

[RMEVET]

You could pull the fuel line when it shuts down and make sure it is getting fuel, fuel problems don't fix their self after 10 mins. The coil will act like that also, hope it's fuel but don't rule out the coil if you're getting fuel, can you see rust in the tank?

Thank you, Sir! Great point, I will try this!

[rickf]

Ok, Pictures!!! They tell a lot about what is going on. So your vent line is correct. The line from the fuel pump to the air cleaner is kind of correct, it should be a hard line to a "T" at the air cleaner meeting at the same place as the other vent line. I see three fan belts and you mentioned the fuel pump so we are working with an A2 engine, also with the 60 amp alternator I see. I see the factory fuel filter is screwed directly into the carb, this is not good since the original fitting for the carb has straight threads and the filter has tapered pipe threads. If you tighten that filter to tight it will split the opening and the carburetor is instant junk. I do see the extra inline filter and that is good since it will catch anything before that stock filter. When you do your fuel flow check do it before and after the inline filter, only take the stock one out if you suspect that one may be an issue. What I have done on my vehicle is I ran a drill through the stock filter so it is hollow and nothing in there to clog and I run an inline filter as my primary filter. That way I still have the original equipment look and the better inline filter efficiency. When the vehicle shuts off does it backfire a few time as it is dying? or does it just shut off dead? If it is backfiring that is a symptom of a coil or electronic module going bad. More likely a coil.

[rickf]

Ok, I was just looking closer at your picture and I see you are running the A2 carb vapor return line back through the firewall. I assume you have that plugged into the tank and if you do and if it is the original early and then the only place to plug that in is the port for the vent to air cleaner line, which is not connected in this picture. This, in effect, makes it a closed system and can be causing your problem if the cap is not venting. In your setup for an early 151 that vapor return needs to be plugged off. You do not have anyplace in the tank to put it ant it is really not needed anyway. Can you show a pic of the tank so I can see what tank is in it? I am thinking this vehicle has had a lot of things changed around in it.

[RMEVET]

Sir,

Again, thank you! I appreciate all your input!

It does not backfire when I shut it off.

Slide1.jpeg

Slide2.jpeg

Updated pictures attached.

Kirk

[rickf]

Ok, You have an emissions gas tank with a bunch of the emissions stuff blocked off and a non vented gas cap. The gas cap is definitely going to be one of your problems. I am not sure if what that vent line is connected to is a vent or not, I will have to look up the diagrams for the emissions system tank.
You said this is a 1962? I am seeing an A2 engine and charging system and an A2 gas tank. If this is a 62 man have some changes been made! You will need to get an early vented gas cap since all of the emissions equipment has been removed from the tank and blocked off. And as far as my question on the backfiring, I was asking if it backfired when it died while you were driving it and then would not start until it cooled off. I see on your picture notes you say filter is drilled out, did you do that before or after I mentioned it? Please tell me you did not do it while it was installed on the carb?! If so there will be all kinds of crap in the carb now.

[Horst]

I can't imagine that the gas cap is the issue as the tank is vented through that new rubber line connecting it to the air filter. But as said before, quick check to exclude it is to test without the cap at all.

[rickf]

Horst, I have been told, but I have never verified, that the vent line from the tank to the air cleaner is one way. It will only vent excess pressure from the tank to the air cleaner. With an emissions tank I am pretty sure that does not even happen since all vapers are routed to the charcoal canister and then stored there until the engine is run and recycled back through the intake, air cleaner in this case, but through a different line routing. So the port he is using may or may not be a vent. It would be easy enough to check by taking the gas cap off and blow some air back into that rubber line. If it comes out in the tank then vent issue is moot point. Have to make sure the vapor return from the carb is routed into the correct port on the tank also.

The actual best way to do this would be to get the correct tank for the early vehicle or even an early A2 tank. The early A2 tank is exactly the same as the straight 151 and A1 tank but without the electric pump. Just a different top cover. Those tanks are getting hard to find and expensive.

[RMEVET]

Thank you both, for all the information.

I only say 1962 because the data plate on the inside reads 4/62.

So you recommend testing it with the fuel cap off or loosened?

I drilled out the fuel filter when I rebuilt the carb (not attached to the carb).

Kirk

[rickf]

How about a couple pics of the vehicle itself? Front, back and engine compartment and at least one side shot. from that we should be able to determine what you actually have. the data plates are changed a lot on these when people need a title and they have a plate with a matching title. Since there are no serial numbers on the vehicle the data plate is all there is. I can tell you where to look for the body tag but it would help if I knew what vehicle we were starting with. And yes on the loosened gas cap.

[RMEVET]

Sir - again thank you!