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Fuel issue, '12 HPX Micro


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Hello! First post, I'll try to make this as brief as possible!

2012 Maverick HPX Micro, Yamaha F40LA, fuel injected.

Bought the boat used in September. I've had issues running premium gasoline (E10) through it. It will bog down and act like theres no fuel, I have to pump the bulb and idle for a while for it to act normal again. Does it every time I take the boat out.

Called the guy I bought it from, said he ran ethanol free in it, and it wont act up. In Houston, you can't get ethanol free. Have had 2 certified Yamaha technicians at 2 shops look at it. Changed fuel pump, anti-siphon valve, cleaned nozzles, the works. Still messed up.

I guide in Louisiana during the winter, where I can readily get ethanol free. This immediately solved the issue, boat ran like a champ. However, after 3 months, it started doing the same thing again, on the ethanol free fuel! I found that along with pumping the bulb and idling, sometimes it would help to open the fuel cap.

A few weeks ago, i also started experiencing problems when I fuel up at the station. I may have half a tank, but as soon as I start fueling, the fill hose will catch and trip the gas pump to stop filling. I may need to put 7 gallons in, but i can only get 1 gallon or less. If i shake the boat a little, or drive around the block, sometimes it would fix the issue.

This leads me to believe my fuel related issue is more of a ventilation problem. Has anyone run into this sort of thing?

Sorry for the long description. I'll call Maverick if i need too, thought I might be able to get some feedback from somebody with a similar issue or someone that has heard of this.

Thanks in advance!

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Sounds like a kinked overflow line...or clogged..

Sometimes critters get up in them and die, or you have a kink in the line....

Also, ***uming they changed out the fuel ball and used only an OEM Yamaha?

Is there anything different in the fuel lines...nothing restricting it or a turn, etc.?

Take the overflow valve line off and blow it out to be sure....


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no restrictions at all, all smooth turns. i've blown on the vent / overflow before, no problems. plus fuel regularly squirts out the side when i do get a full tank.

also wondering if the anti-siphon valve ball bearing is getting stuck and restricting fuel flow of some sort.

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In your original post you say someone changed the anti-siphon valve already, so it's not likely it's bad already.

Seems like you have two different problems; a fuel restriction and a vent problem when fueling. Have you tried filling very slowly. Do you have a fill/vent combination or is the fill and vent two separate items?

What type of water separator do you have? Some are too restrictive for smaller motors. Has to do with the microns.

Does you fuel line plug into the motor or is the fuel line continuous from the bulb to the fuel pump?

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