vapor lock/ poor ventalation

[blackbomber]

Hey guys,, its me Jason, and the old 84  bomber,,,   First of all,  what exactly is vapor lock...second,, how does my gas tank vent on the truck....and third,,   is it easier to get vapor lock with only a few gallons in the tank.... thanks guys .. :thumbup:

[datzenmike]

Vapor lock has nothing to do with the gas tank. Classic vapor lock is when the fuel in the lines, the pump or the carb boils into a vapor. The pump is designed to pump a solid not a gas and fuel pressure will drop, the carb may empty and the engine quit or not re start. It's much more common that engines that vapor lock simply refuse to re-start. The good news is that since the mid '70s a fuel return line is used to circulate cool gas from the tank past the carb. There is much less chance of vapor lock with this set up.

 

Modern gas tanks are sealed by the gas cap. Any vapors from evaporation are vented through a tube into the engine compartment into a charcoal canister filter and stored. On the next start up, engine vacuum draws these stored fumes into the intake where they are burned. During running, as the fuel level drops, air is drawn into the tank to replace the fuel removed by the same vent line.

[blackbomber]

Thanks mike... yea I thought it had something to do with that canister on the front driver side.... its original canister...  can I test it ...clean it ....or replace it maybe... and what is the actual name of the canister... thanks.      Jason..... 

[datzenmike]

Everything is called the evaporative emission control system. It's to reduce evaporated hydrocarbons escaping into the atmosphere. The system consists of...

 

The fuel tank with positive sealing cap

Fuel check valve. Prevents fuel escaping out the vent pipe if in a roillover

Vapor vent line

Carbon canister*

Vacuum signal line. Sucks fumes into intake

Canister purge line. Vacuum signal that open the cannister purge line.

[Charlie69]

Vapor lock is a thing of the past mostly unless some one modifies a new fuel system. 

 

The new fuel systems have a fuel return line and the pumps run continuously and the unused fuel either from the carburetor or the fuel injection system returns to the fuel tank and this fuel is then cooled in the tank by the fuel in the tank.  This helps to keep the fuel being delivered to the carburetor or the injection system cool for better vaporization of the fuel.  The result of this is no more vapor locking.

 

If some one blocks off the return line the there is a chance of vapor lock on a newer vehicle.

 

Mike what year did Datsun/Nissan ad the fuel return lines.  I have seen one on a 1976 Datsun 620 with an L20B

 

720 fuel delivery and return line

 

620 fuel delivery, fuel return line, and vacuum line

[datzenmike]

Definitely on all L20Bs so '74 was the earliest one on the 610 I believe. They were on the 240z cars because.... SUs. Perhaps others.

[MikeRL411]

When all else fails, replace the filter element on the charcoal cannister!  It's usually on the botom and can clog with crap stirred up from the road and front tires.