M40D Fuel Line Size

[scout-j-m]

I have Tohatsu M40D carbs on my 1988 Yamaha 30. Until recently they had the thick black fuel line connecting them together with the fuel pump. I threw it away and put on some 1/4" ID Tygon translucent yellow line. It is now leaking at the connection to the elbows on the two carbs without the fuel pump. The inlet/outlet of the fuel pump is not leaking, however, nor is the connection between the fuel filter and quick connect in the lower cowling. I found some 1/4" line like I removed and it goes on much more snug and probably wont leak. Just wondering if indeed 1/4" is the correct size? If so, maybe since the Tygon is more flexible with a thinner wall I should drop down to a 3/16" line. I really like to see the fuel flowing on multi carb motors so if there is an issue on the water I can verify that one carb isnt starving for fuel and running lean.

Also, the 90 degree elbow is a little loose where its threaded in the carb. Will any fuel resistant RTV from the auto parts store be ok to seal that up with?

 

[pvanv]

The fuel line is supposed to be 5mm (3/16).
The elbow does not thread in. If it is leaking, you will need to either replace the carb (ouch$), or cobble up a weatherhead or other brass fitting to go on the carb. Those plastic parts never were available separately.

 

[scout-j-m]

The fuel line is supposed to be 5mm (3/16).
The elbow does not thread in. If it is leaking, you will need to either replace the carb (ouch$), or cobble up a weatherhead or other brass fitting to go on the carb. Those plastic parts never were available separately.

Thank you Paul. I have some 3/16 line in my shop I can swap it out with.

Not good news on the fitting lol. It definitely has a little play but I'm not certain it is actually leaking....could just be fuel from the oversized hose on the barb. Hopefully it is not. However, if it indeed is I'll do a little more digging and try to maybe replace with a bress one. I know I have seen similar Yamahas with these Tohatsu carbs where its been done since they are restacked with the fuel pump in the middle vs the bottom.

 

[scout-j-m]

Thank you Paul. I have some 3/16 line in my shop I can swap it out with.

Not good news on the fitting lol. It definitely has a little play but I'm not certain it is actually leaking....could just be fuel from the oversized hose on the barb. Hopefully it is not. However, if it indeed is I'll do a little more digging and try to maybe replace with a bress one. I know I have seen similar Yamahas with these Tohatsu carbs where its been done since they are restacked with the fuel pump in the middle vs the bottom.

Well, the 3/16 I had was incredibly hard and I didn't want to break the plastic elbows so I didn't force it. Ordered 3/16" Tygon and will try that. On top of the fitting leaks, the carb with the fuel pump has a sticking float so there is fuel going everywhere at the moment lol. But also ordered 3 new float valves and bowl gaskets. Hopefully I get all of this resolved in the next week or so.

 

[pvanv]

Yeah. Regular Tohatsu or Yamaha line is pretty flexible.

 

[scout-j-m]

Yeah. Regular Tohatsu or Yamaha line is pretty flexible.

Is there any OEM line that is clear or is it all black? I've never had this much trouble getting the clear line I use to seal. I may end up putting solid lines between the fuel pump and carbs and using clear line immediately before and after the filter. At least that way I can trace air bubbles and monitor fuel flow to the fuel pump.

 

[pvanv]

No outboards use any clear fuel lines.