Originally Posted by Franklin2

You never did say if your truck is completely stock. Exhaust is stock and in the factory spot as well as the fuel line. If any of that has been changed, it can aggravate the vapor lock problem. If you have a long piece of hose somewhere under the truck that was put in place of the stock metal fuel line, that can be a problem also.

The usual place for problems is the drivers side frame rail where the fuel line comes up and approaches the fuel pump. A old piece of heater hose over the fuel line can help insulate it.

Originally Posted by FuzzFace2

ONLY I RUBBER LINE?
Better look again there should be 2 with only 1 tank and 6 with 2 tanks unless you have EFI then no rubber lines.
you should have a rubber line at each tank to metal line.
3 at the switch valve and 1 from metal line to pump.
That is on a 300 six duel tank truck.
Dave ----

Originally Posted by kr98664

Sounds like it's time for a new sender. About $30 or so, avoid the cheap brands:

https://www.rockauto.com/en/moreinfo...t=4588&jsn=939





Glad to hear the performance is back. The hissing is still a problem. That's not normal. Time for a new brake booster, even if the vacuum leak doesn't seem to affect performance.



Ah, good ol' vapor lock. Careful, because that's a catch-all term for several heat-related fuel issues. There are many things you can do to minimize the effects. Just remember to keep in mind the situation isn't really just one problem. Several factors are at play.

1) The mechanical fuel pump, up at the front of the engine, can have a hard time drawing warm liquid fuel all the way from the tank clear in the back. Note I said "liquid". As fuel heats up (high ambient temperature and adjacent exhaust), it easily turns to vapor, especially due to suction from the pump. The pump ends up drawing vapor, not liquid. This is the old-fashioned vapor lock you may hear mentioned. The carb runs dry because the pump is moving vapor, not liquid fuel. The fix for that is to insulate the lines and switch to an electric pump back by the tank. With the line pressurized, fuel doesn't turn to vapor:

https://www.ford-trucks.com/forums/1...tallation.html


2) The other big issue is fuel heating up in the carb float chamber. This causes hard restarts when the engine is warm. This is known as heat-soak. I'm not sure of the exact fault sequence, but after you shut off the engine, the underhood temperature spikes up. Twenty or thirty minutes after shutdown is the worst. The fuel sitting in the float chamber gets hot and foamy. I don't know that it necessarily boils over, but it might. But no matter the exact cause, the carb is not happy with this hot foamy fuel (or lack thereof if it boils dry). You have to crank and crank and crank the starter to get cooler fuel to replenish the float chamber, and then finally the engine will start. For this heat-soak issue, the main fix is to limit heat reaching the carb. A phenolic spacer will help. I kept that and added a large heat shield extending out from the base of the carb. On my '84 351W, I even went so far as to fabricate a shroud around the carburetor, cooled by the AC system. You can read lots more details here, starting with post #6. Read that, and you will see I even had heat-related issues while driving until I blocked off the exhaust crossover passage. The problem would start shortly after the engine had been working hard, and was just loafing along:

https://www.ford-trucks.com/forums/1...l#post16083555

This next link has more details about blocking off the crossover passage on a 351W. Obviously the specifics don't apply to your 300-6, but some of the general ideas will. I'm not sure what you can do to limit the exhaust heating the intake manifold on your engine:

https://www.ford-trucks.com/forums/1...r-passage.html


The next thing you can do is be careful what fuel you are using. Specifically, with modern fuels, you want to run the lowest octane fuel possible. Way back when, it used to be higher octane fuel was more heat resistant, but not so anymore. It's just the opposite today. Lots of good info at this link:

https://www.ford-trucks.com/forums/1...g-and-you.html


As far as fuel, I have found some brands are MUCH more heat resistant than others. Personally, I have found Chevron brand to be the most heat resistant. On several occasions, when I've used other brands, I've had heat-related issues almost immediately. This has happened both with my truck and one of my Jeeps.

From my experience, there was no one magic bullet to fix all problems. It was a little bit here, a little bit there, and so on. I think blocking off the exhaust crossover passage made the biggest improvement, but everything else certainly helped, too.

Originally Posted by xenophone

Everything is stock as far as I know. I mistakenly said there is only one rubber line, but there are two. One from the tank to the metal line on the frame. The metal line runs all along the frame up to the engine compartment, connects to a rubber line which goes to the fuel pump, then metal from there to the carb.

Originally Posted by Franklin2

When they change the formulation of the fuel in your area, that will help also. When the weather gets cold they make the fuel more volatile for better winter starting. Then they change it back when the weather gets warm, but sometimes a warm winter day makes for problems...

Originally Posted by xenophone

Can anyone recommend a brake booster? I'm looking at this one from Power Brake Exchange on Rockauto: https://www.rockauto.com/en/moreinfo...JJ4rUoVxYGY%3D

I prefer to buy American/North American when possible.

Originally Posted by Franklin2

You don't have a autoparts store near you? I see Autozone hs one for $98.00 Shipping is going to start to kill RockAuto. Autozone will give you a lifetime warranty also.

Originally Posted by xenophone

Can anyone recommend a brake booster? I'm looking at this one from Power Brake Exchange on Rockauto: https://www.rockauto.com/en/moreinfo...JJ4rUoVxYGY%3D

I prefer to buy American/North American when possible.

Originally Posted by Franklin2

You don't have a autoparts store near you? I see Autozone hs one for $98.00 Shipping is going to start to kill RockAuto. Autozone will give you a lifetime warranty also.

Originally Posted by xenophone

I see a Duralast on Autozone. I'm happy to pay more for American made, which I believe Power Brake Exchange is.