Best setup for internal and external gas tank usage in a Tohatsu 4-stroke 4HP

[alberg22]

I've owned a 2009 MSF4BL (4 stroke, 4 HP, with dual tank) for a couple of years but still am unsure about the fuel **** and vent screw setups to operate with the internal and/or the external tank:

The fuel **** on the port side of the engine is closed when horizontal and open when vertical. Does this pertain or affect the internal tank? the external tank? or both? (I suspect it only pertains to the internal tank, which means that when operating the external tank it should be closed (i.e., horizontal?).

I noticed that when the stopcock is open (i.e., in its vertical position) and the air vent screw of the internal tank is open, the bulb in the fuel line can pump gas from the external into the internal tank. Is this normal?

If this is normal, then I suspect that when using the external tank with the stopck **** open (vertical), the air vent screw of the internal tank (i.e., the one on top of the engine) must be kept closed? (to allow for enough suction from the external tank).

When operating with fuel from the external tank should the air vent Screw at the top of the engine: closed or open (?) and the fuel **** closed (horizontal) (?) or could the Fuel **** be open and the air vent screw at the top of the engine closed (?).

Thanks.

 

[pvanv]

Re: Best setup for internal and external gas tank usage in a Tohatsu 4-stroke 4HP

The fuel **** is only for the internal tank. To run on the external, close it.

Yes, one could fill the internal tank from the external if the fuel **** is open.

If you are connected to the external tank, and the **** is open (and the onboard vent is open), you are set to run from the onboard tank, and will use up the fuel from the internal tank, then suck air and stall (as long as the external tank is below the motor's tank).

To run from the external tank, close the fuel ****. If not using a tank, close that tank's vent.

 

[alberg22]

Re: Best setup for internal and external gas tank usage in a Tohatsu 4-stroke 4HP

Excellent! so, if I understand correctly these are the possible setups:

a) using onboard (internal) tank:
Both fuel **** and onboard vent: open (fuel **** is open when vertical)
Vent of the external tank: close

b) using external tank:
Both fuel **** and onboard vent close (fuel **** s close when horizontal)
Vent of the external tank: open

To fill the onboard tank directly from the external tank:
Keep both vents and fuel **** open
Pump the bulb in the fuel line while being careful not to overflow the onboard tank (better done without the engine cover...)

Much appreciated.

The fuel **** is only for the internal tank. To run on the external, close it.

Yes, one could fill the internal tank from the external if the fuel **** is open.

If you are connected to the external tank, and the **** is open (and the onboard vent is open), you are set to run from the onboard tank, and will use up the fuel from the internal tank, then suck air and stall (as long as the external tank is below the motor's tank).

To run from the external tank, close the fuel ****. If not using a tank, close that tank's vent.

 

[pvanv]

Re: Best setup for internal and external gas tank usage in a Tohatsu 4-stroke 4HP

Yep. But be careful trying to fill the onboard tank that way, as it would be easy to overflow it. Most people will disconnect the fuel primer hose when running inly on the onboard tank, btw, even though the check valve should prevent the onboard tank from draining into the external tank.

 

[Sea Rider]

Re: Best setup for internal and external gas tank usage in a Tohatsu 4-stroke 4HP

Paul, is that info applicable also to 2 strokes 5 HP internal/external gas tanks ?

 

[pvanv]

Re: Best setup for internal and external gas tank usage in a Tohatsu 4-stroke 4HP

The M5B came as either internal tank or external tank. If you have modified one for dual tanks, yes, it would work the same, as long as you are running the check valve. Otherwise, having both tanks, and the fuel **** open, allows fuel to flow by gravity to the lower, external tank. Also, if you try to operate from both tanks with the **** open, you will do nothing but run from the upper (integral) tank until it is dry, then suck air and stall.

 

[WWWoody]

This helped me understand and run my external tank. Thank you all.

 

[Sea Rider]

During summer some fuel leakage has been reported on internal tank due to extreme pressure build ups inside tank when fuel **** valve and tank vent are completely closed.



If this condition occurs, remove internal gas hose from lower tank, wrap several generous rounds of teflon tape on tank's neck, slight lube teflon wrapping for smooth hose re insertion on neck, once hose is evenly seated, secure with 2 tie wraps or metal clamp well tight.

Happy Boating