Vapor Lock?

[JSinMO]

That's exactly how my 442 behaved when vapor lock happened. The vapor locking causes a fuel shortage, and by choking it you can increase your fuel "suction" to keep the engine running, albeit poorly. This sounds precisely like vapor lock to me.

Bob

Seems to me this is what’s happening. Even with full choke it barely runs. If you try to do anything other than keep it running it will die.

To update this I ran it some today and it happened again. I didn’t have a lot of time to dig into it, but I did check a couple of things.

I checked the fuel pump and it is working fine.
Then I moved the gas line and took the curve out of it to the carburetor as much as possible. Tractor started up and ran better with no choke. This is new fuel line but I don’t think it can handle the heat. The line right at the carburetor feels very soft, I can pinch it shut with very little pressure. This would explained what happening.

So as soon as I can get to a store I think I’ll look for some copper line to replace the rubber hose and run it out of the engine compartment as quickly as possible.
On the old tractors guys used to make a couple of coils in the line to try to keep the fuel cool on the way to the carburetor, I might try that too as there really seems to be quite a bit of heat build up under the hood.

I’ll update this when it get it changed.

[propane1]

Still not making sense to me. As I’ve said. I have no experience with this. But, if it’s a vapour lock, that means a space some where in the system has vapour not liquid in it. If the carb bowl was down on fuel, that would mean the needle is open and fuel should run in. The bowl in the carb has to have a atmospheric hole in it to allow gas in to the bowl while vapours get pushed out. The electric fuel pump should be able to do that. It’s pressurizing the fuel to the carb and should be able to push fuel into to the carb bowl. If the atmospheric hole in the carb is not plugged. Then the needle will close to stop fuel coming in.


Jumpins. That was quite a ramble. Beat that Eugen.


Noel

[thebuildist]

So as soon as I can get to a store I think I’ll look for some copper line to replace the rubber hose and run it out of the engine compartment as quickly as possible.
On the old tractors guys used to make a couple of coils in the line to try to keep the fuel cool on the way to the carburetor, I might try that too as there really seems to be quite a bit of heat build up under the hood.

I’ll update this when it get it changed.

If you go with a copper line, you might sheath it in rubber hose down near the engine, so the rubber acts as insulation to keep the copper from heating up.

Bob

[JSinMO]

So as soon as I can get to a store I think I’ll look for some copper line to replace the rubber hose and run it out of the engine compartment as quickly as possible.
On the old tractors guys used to make a couple of coils in the line to try to keep the fuel cool on the way to the carburetor, I might try that too as there really seems to be quite a bit of heat build up under the hood.

I’ll update this when it get it changed.

If you go with a copper line, you might sheath it in rubber hose down near the engine, so the rubber acts as insulation to keep the copper from heating up.

Bob

That’s what I was thinking too.

[JSinMO]

Still not making sense to me. As I’ve said. I have no experience with this. But, if it’s a vapour lock, that means a space some where in the system has vapour not liquid in it. If the carb bowl was down on fuel, that would mean the needle is open and fuel should run in. The bowl in the carb has to have a atmospheric hole in it to allow gas in to the bowl while vapours get pushed out. The electric fuel pump should be able to do that. It’s pressurizing the fuel to the carb and should be able to push fuel into to the carb bowl. If the atmospheric hole in the carb is not plugged. Then the needle will close to stop fuel coming in.


Jumpins. That was quite a ramble. Beat that Eugen.


Noel

Your thinking of it correctly. So the carburetor is working as it should. The needle is opening and calling for fuel to the bowl. The problem is the gas line is partially restricted because its collapsing in the bend in it just before the carburetor. The fuel pump is pressurizing the system, but when the fuel gets to that part of the line, the restriction plus heat is vaporizing the fuel before it makes it to the bowl. In this situation the fuel keeps turning to vapor and never fills the bowl.
That’s why it’s a vapor lock liquid fuel can’t get past it.

I alway worry I’m not explaining things very well, so I hope that makes sense.

[JSinMO]

Still not making sense to me. As I’ve said. I have no experience with this. But, if it’s a vapour lock, that means a space some where in the system has vapour not liquid in it. If the carb bowl was down on fuel, that would mean the needle is open and fuel should run in. The bowl in the carb has to have a atmospheric hole in it to allow gas in to the bowl while vapours get pushed out. The electric fuel pump should be able to do that. It’s pressurizing the fuel to the carb and should be able to push fuel into to the carb bowl. If the atmospheric hole in the carb is not plugged. Then the needle will close to stop fuel coming in.


Jumpins. That was quite a ramble. Beat that Eugen.


Noel

Your thinking of it correctly. So the carburetor is working as it should. The needle is opening and calling for fuel to the bowl. The problem is the gas line is partially restricted because its collapsing in the bend in it just before the carburetor. The fuel pump is pressurizing the system, but when the fuel get that part of the line, the restriction plus heat is vaporizing the fuel before it makes it to the bowl. In this situation the fuel keeps turning to vapor and never fill the bowl.
That why it’s a vapor lock liquid fuel can’t get past it.

I alway worry I’m not explaining things very well, so I hope that makes sense.

This is why the engine will try to idle with full choke, it’s literally trying to run on fumes.

[propane1]

Ok, I got it now. Thanks.


Noel

[DavidBarkey]

@JSinMO Instead of copper line , what about fuel injection hose . Double walled stronger hose.

[propane1]

Here’s another ramble for you. If you use copper line, and cover it with another line, rubber, plastic or what ever. I would get the covering line much bigger than the copper line. That way you have an air space. And leave it open on both ends. Have the end farthest away from the carb as low as you can get it. This will cause a venting action in the covering hose. As things get hot the hot air will rise and draw cooler air in from the bottom to help cool the copper pipe. If you have the covering line tight to the copper, the copper will draw the heat in from the covering pipe.


Noel

[DavidBarkey]

After reading what he found , I don't thing heat persay is the issue . There are many here with these 646/8 that are not having the same problem . I have side panels on Frankie's hood and work him hard and don't have that issue with a P220 onan . I think that the quality of line just is not up to scratch for this application . I have had to use fuel injection hose instead of lose pressure hose in some applications due to the poor quality hose these days kinking or collapsing . My 2 cents , You may keep the change .