Tohatsu M9.8B 2-stroke and Tohatsu EPA tank

[cprstn54]

Do I need a fuel line with the pressure device with this combo?

Why can't I just open the screw vent and use an existing line with a bulb like in the old days?

Ken C

 

[pvanv]

Thank your US EPA for the pressure/vacuum tanks. Theoretically, there will be fewer fumes evaporate into the atmosphere with them. No, the demand valve is not needed, but you MUST disconnect the fuel line when not running to avoid over-pressurizing the pump and carb when the tank pressure rises in the sun if you use the EPA tank without a demand valve. The old-style vented fuel cap/gauge is still available (hint hint). Likewise, some run the newer tanks, but leave the cap slightly loose to act as a vent.

 

[cprstn54]

No, the demand valve is not needed, but you MUST disconnect the fuel line when not running to avoid over-pressurizing the pump and carb when the tank pressure rises in the sun if you use the EPA tank without a demand valve.

Hi, Paul.

Thanks.

After an hour of additional web research, I think the manual vent on the new tanks is what gives you venting down to 5 PSI. Even with the vent open, there will be 5 PSI of fuel pressing on the float bowl valve, which is less pressure than most carb fuel pumps (6-8 PSI). It would appear that you are correct and don't need an FDV if the ,manual vent is left open.

However, Tohatsu says you *must* use an FDV with its 4-stroke engines and this tank. Are the 4-stroke float bowls different from the 2-strokes?

Ken C

 

[pvanv]

The thumbscrew on the new tanks merely closes off the vent "absolutely". Opening the thumbscrew does not vent anything, but allows the 5 psi vent to work. It's a terrible design (in all tanks of all brands) and sometimes the vents stick, allowing much higher pressures than merely 5 psi. They can also allow a significant vacuum to develop in the tank. These tanks can look like throw pillows, or appear to be crushed.

I doubt the fuel pump on a 9.8B will ever deliver more than 3 psi. It's always good practice to disconnect the primer hose when not running. In the case of 4-strokes, extra pressure can rupture the fuel pump diaphragm, and dump fuel into the crankcase. On the carb side of things, the float valve can weep, also flooding the intake with fuel, and possibly getting down into the crankcase.

Current production does not use a fuel demand valve at all, even on 4-stroke motors. When they went with an improved-sealing motor-side fuel connector in 2012, they deleted the fuel demand valve.

 

[Sea Rider]

Both are same and work same. Tohatsu does not endorse on new fuel tanks unscrrewing a bit fuel cap to release pressure building inside them. Much worse during use due to fuel spills that could eventually ignite and kabum. Will those tanks turn piggy round when at sun before vents down to 5 PSI ?

Happy Boating