# Tiller fuel system basic question



## FlatCat (Aug 18, 2007)

I have a Merc 40 2 cycle. I think it has an air leak in the fuel line.
Portable tank, line, bulb, connections are all new.
Pump bulb, start, runs fine for a few min then it will only rev to bout 2800 rpm's. I can see air pocket in fuel filter.

Would a small air leak cause this type problem?


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## mark_gardner (Mar 18, 2009)

i would check all connections cause it sounds like she's sucking air from somewhere :-/


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## Flpt (Nov 11, 2007)

Check the fuel outlet on the tank, the black plastic outlets tend to crack at the threads where the brass fuel line connector screws in.


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## FlatCat (Aug 18, 2007)

I will thread tape and double hose clamp all connections to be sure.

I'm guessing an air leak would cause this type of issue, or is a small leak no big deal?


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## DuckNut (Apr 3, 2009)

Once upon a time I had a motor that acted the same way. After I replaced all of the hoses, priming bulb, etc. it still acted up at higher rpms. Ran great at low rpms.

Mine had a mechanical fuel pump attached to the engine (a small box looking thing) that the fuel line went into and then a line into the carb. Inside that box thing there was a plenum (thin rubber gizmo) that created a vacuum to pull gas from the tank as well as a pump to keep the carb full of fuel. After a guy showed me this and I replaced it the motor was perfect.

I was not able to see the fine deteriation of this with my eye, I had to use a magnifying glass. At high speed there was not enough rigidity to it for it to work properly and caused the pump to create turbulence to the fuel. I think the part was less than $5.


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