Fuel line setup 4xx

   / Fuel line setup 4xx #1  


Platinum Member
May 4, 2010
Jessup Mill, NC
Rk55HC 4n1 fel/bh, Power-Trac 1850, 425d, Terex pt30, Kubota kx033, bx1880, yanmar 8x8 dumper, Magnatrac mh5000 w/ loader, six way blade & backhoe, Dew-eze ATM72LC Slope Mower, Terramite t6 4wd, DR Power brush mower
Hi gang

On my older mystery pt the fuel tank is integral to the engine shroud and there are 2 fuel lines ports piped and 1 drain. Any one with this config able to show/tell how those are supposed to be connected to the filter? One looks straight forward, the other is pipe that is just open and directly under the gas cap...

I'm having mystery shutoffs that sound fuel starved...
   / Fuel line setup 4xx #2  
Sound like one might be a vent? I don't have that setup, so I can't help.
   / Fuel line setup 4xx #4  
I'm having mystery shutoffs that sound fuel starved

Two possible causes:
1. The elbow on the bottom of the fuel tank with the hose that goes to the fuel tank has some plastic debris in it. Almost every single PT4xx owner has reported this. The collection of debris can block fuel flow.
2. You are having problems with vapor lock. The fuel hose is routed near the exhaust manifold. The fuel pump is mounted on the upper left side of the engine near the muffler and gets too hot. The fuel pump is driven by pressure pulses from a tube connecting it to the crankcase, and you can mount the fuel pump anywhere you want; just buy some more 1/4" vacuum hose. I would recommend moving it away from the exhaust manifold or muffler.
   / Fuel line setup 4xx
  • Thread Starter
Thanks for the quick inputs. I think you confirmed that it should be plumbed as a vent. I did that and it's better but still struggling. I'll try to eliminate the heat with some shielding... I think tm is right on the vapor lock.

On my newer pt425, yeah plastic in the tank elbow... +1. In the 4xx mystery machine (predator repowerd) the fuel tank is fabricated in the metal housing...i totally get why they changed that...

This issue is a result of a repower I did to a machine that was doctored (civil war Era doctor) by the prior owner before he realized that he had a cylinder problem, not a fuel problem...

I'll update post tinker...
   / Fuel line setup 4xx #6  
The predator has a carb, and not fuel injection, correct?

I mention that because if it had fuel injection, there'd probably be a fuel return line.
   / Fuel line setup 4xx
  • Thread Starter
Yep MR carbed. It's exactly like any honda v twin in lawn equipment.

Seems like a 3 strike situation, need to complete the vent loop, isolate heat and the 3rd strike still to be called is either need vented cap and / fuel filter change
   / Fuel line setup 4xx #8  
It never hurts to change the fuel filter and it's cheap.

On your mystery shutoff fuel starvation issues....

Your tank is in the engine cover. My tank is the plastic one inside the engine compartment. I had an issue with the engine dying, and quickly determined it was when the fuel level in the tank got lower than the level of the carb. It was my fuel pump. It developed a pinhole in the diaphragm and lost vacuum.

That can't happen in your situation because your fuel tank is always higher than the carb, correct?

Anyhow, the fuel pump is just one more component to consider.
   / Fuel line setup 4xx
  • Thread Starter
Hey Mr thx for scratching your head on this issue...

I've been through the scenario you described. And you're right due to the setup it's unlikely BUT it would take very little change in pressure to eliminate the differential...

The engine is a predator... So anything is possible!