1998 Yamaha 115 2 stroke - Running on portable 6 gallon tanks

[BOAH]

I have an older boat with no internal tank so I have to run this motor on portable 6 gallon tanks. I have two older Atwood tanks and one old Sea Sense tank. All three tanks have the vent screw in the gas cap. I don't have any problems with the Sea Sense tank. That one works great. With the Atwood tanks, (one especially) when I'm running at a high speed for a period of time, I've been getting a vapor lock. Meaning that the primer bulb gets sucked flat and the engine stalls.

Trying to diagnose it on the water yesterday, I ran it for a few minutes at a higher speed and noticed that the bulb wasn't hard so I cracked the gas cap to let more air in and the bulb immediately sucked all of the way flat and the motor stalled.

Apparently I don't understand how this should be working am completely baffled. I would think that letting more air into the tank would have helped. Any clue?

Thanks for your help.

 

[hemi rt]

Sounds like the pickup in the tank is either plugged or it is sucking something off the bottom of the tank thus plugging the pickup; a good rad shop should be able to clean the tank so it is spotless inside

 

[99yam40]

Bulb collapsing is a sign of restriction before the bulb not vapor lock

 

[robert graham]

The later model, EPA mandated tanks are designed without vents to prevent fuel vapors releasing into atmosphere....leave the cap cracked open just a bit while running to help vent tank.....

 

[BOAH]

Thanks! I ended up buying a couple new Moeller tanks and at the same time purchased a couple new gas caps with the manual vent.

 

[99yam40]

did that fix your problem?

I would not think that opening the cap could cause the bulb to get sucked flat if the tank vent was a problem

 

[BOAH]

I agree. Kind of makes sense to me if the pickup is partially clogged. To take that out of the equation, I ended up buying 2 new moeller tanks. Got them today and am happy to report that they came with the manual vent in the cap. Very happy with that. Will run it this weekend and report back.

 

[BOAH]

Speaking of the new tanks, what do you use on the threads of the new tank when installing the hose connection. Can I use plumbers tape?

 

[99yam40]

need to find some made for gas

 

[BOAH]

I ran the motor for two solid days and the new Moeller tanks worked very well with the motor.