Quadruple bypass? 7/24/13

[rover67]

While I was changing the oil in the 60 today, I took a close look at the fuel routing. Then I slapped my forehead. D'oH! There is only one line to the carb. There are two lines from the frame to the fuel pump (one with filter is obviously the inlet). Obviously the return is between the pump and the tank, not the pump and the carb. This would make the fuel in the line between the pump and the carb hotter, but it is under pressure so it shouldn't boil as readily as the inlet between the tank and the pump which is under negative pressure.

Yeah that's what Bruce and I were saying, the 60's have a return to tank from the pump.

The only issues I had on the suction side of my rigs fuel system was when i was running a high volume external pump for my fuel injection. It would cavitate due to the hot fuel vaporizing under vacuum on the suction side.

Went to in tank pump and problem solved.

My 40 with a similar fuel system (block mounted pump with return to tank) runs fine. It has not "vapor locked" on days when other people's rigs have. I am not sure what the difference is, but I do think that holding the fuel system at an overall higher pressure helps... so maybe it is a rig with a leaky fuel cap or vent system that won't allow pressure to build lets the fuel boil faster?

 

[Rzeppa]

Yeah that's what Bruce and I were saying, the 60's have a return to tank from the pump.

The only issues I had on the suction side of my rigs fuel system was when i was running a high volume external pump for my fuel injection. It would cavitate due to the hot fuel vaporizing under vacuum on the suction side.

Went to in tank pump and problem solved.

My 40 with a similar fuel system (block mounted pump with return to tank) runs fine. It has not "vapor locked" on days when other people's rigs have. I am not sure what the difference is, but I do think that holding the fuel system at an overall higher pressure helps... so maybe it is a rig with a leaky fuel cap or vent system that won't allow pressure to build lets the fuel boil faster?

I think the later 40 system is better than the 60 system. The later 40 system basically is constantly recirculating from the tank to the carb and back to the tank, keeping the fuel cooler. The system on 60s recirculates from the pump to the tank, but the end from the pump to the carb is a dead end and can get hot. The main thing it has going for it is being under pressure, so it has a higher boiling point.

Of course putting the pump in the tank solves one problem while creating another when it is time to replace it.

 

[subzali]

Carson, how is your timing? Sometimes if your timing is off it can affect how it starts.

 

[cbmontgo]

Carson, how is your timing? Sometimes if your timing is off it can affect how it starts.

Timing is set. She starts and runs perfectly except for this particular issue when it's hot.