2006 Yamaha F115 fuel leaks from VST

[Jim Kross]

My Yamaha 4 Cycle F115 leaks fuel from the area of the VST, runs rough at half throttle and stalls frequently when shifting into gear. The fuel tank has been cleaned, new filter on the engine, and new injectors. At idle the loss is a steady drip out of the lower cowling. I can't pinpoint where the leak is coming from.

 

[robert graham]

Probably a bad o-ring or gasket….but do not operate the motor until leak is repaired….a real fire hazard!!!

 

[Jim Kross]

As you likely know the VST is hard to get to requiring the mechanic to remove most of the throttle body and the fuel systems. Any recommendations?

 

[99yam40]

easiest way to find where it is coming from is to remove the cowling, clean everything up and let it dry.
have someone turn the key on and watch for any leaks.
if no leaks seen, have them fire it up while on muffs while you look for leaks.
fire extinguisher may be good to have handy just incase

the level in the vst should not get high enough to leak out of the top or gasket unless the float does not close off the needle into the seat

 

[Jim Kross]

easiest way to find where it is coming from is to remove the cowling, clean everything up and let it dry.
have someone turn the key on and watch for any leaks.
if no leaks seen, have them fire it up while on muffs while you look for leaks.
fire extinguisher may be good to have handy just incase

the level in the vst should not get high enough to leak out of the top or gasket unless the float does not close off the needle into the seat

I cleaned it up this afternoon and will let it sit overnight. In the morning I will look for leaks the turn on the key and inspect the VST and hoses and then start the engine and look further for leaks. It's a difficult area to inspect because the air intake an throttle body cover the VST. I purchased enough parts to rebuild the VST assuming it has no corrosion holes.

Thank you for the advice.

 

[Jim Kross]

I cleaned it up this afternoon and will let it sit overnight. In the morning I will look for leaks and inspect the VST and hoses. It's a difficult area to inspect because the air intake an throttle body cover the VST.

Thank you for the advice.

After the cleanup and sitting overnight I primed the fuel system with the fuel bulb. Using a borescope I inspected the VST and all the lines and fittings associated with it; no current leaks or indications of former leaks. However, when I got near the fuel rail the camera showed a small drip and an accumulation below the intake fitting on the bottom. The fuel system diagram shows that this fitting is attached to the fuel rail with two screws and is sealed with a large O-Ring. The fitting continued to leak until the pressure from the priming bulb ran out.

Removing the screws to replace the O-Ring requires removing the fuel rail and injectors. The attachment screws were tight but when the fitting was removed and the O-Ring exposed, it was slightly deformed. I was surprised to find that this O-Ring was bad. After I replace it I'll report back.

Thank you for the help.

 

[Jim Kross]

After the cleanup and sitting overnight I primed the fuel system with the fuel bulb. Using a borescope I inspected the VST and all the lines and fittings associated with it; no current leaks or indications of former leaks. However, when I got near the fuel rail the camera showed a small drip and an accumulation below the intake fitting on the bottom. The fuel system diagram shows that this fitting is attached to the fuel rail with two screws and is sealed with a large O-Ring. The fitting continued to leak until the pressure from the priming bulb ran out.

Removing the screws to replace the O-Ring requires removing the fuel rail and injectors. The attachment screws were tight but when the fitting was removed and the O-Ring exposed, it was slightly deformed. I was surprised to find that this O-Ring was bad. After I replace it I'll report back.

Thank you for the help.

 

[Jim Kross]

Even after replacing the O-Ring on the inlet to the fuel rail the fuel leak slowed dramatically, but I still have a small leak somewhere in the fuel system.

 

[99yam40]

Even after replacing the O-Ring on the inlet to the fuel rail the fuel leak slowed dramatically, but I still have a small leak somewhere in the fuel system.

all you can do is keep looking for where it is leaking