I cant get this merc 40 to idle low any thoughts

[MERC40]

I have 96 40 horse it runs sweet at high RPMs but wants to die when i idle down to shift I took the carbs off put in new gaskets and blew them out,I de-carbed, I put in a new fuel filter, new plugs, fuel sys cleaner, I ajusted the air screws to 1 1/2 turns out (they were pretty close to that) I am thinking about buying a new tank the pick up is rusty but when i push in the ball it blasts fuel out. I bought a fuel pump rebuild kit and I am going to try that.. do I need to replace the low speed jet is that hard. any thoughts.

 

[Bob_VT]

Re: I cant get this merc 40 to idle low any thoughts

Two things could be happening

The low speed circuit in the carbs is partially blocked which means a full cleaning. The low speed jet is normally a needle valve. If you unscrew it all the way you can looks for signs of wear (ie shoulders worn on the tapered portion of the shaft)

The timing on the low end could not advancing soon enough causing an unbalanced fuel to timing ratio. This is normally linkage related and the advance is not picking up early enough.