[cheapNdisgusting]

I bought a used 1984 Mercury 50 hp serial #6540604. It surges at high speed and never really runs wide open. According to my repair manual it is probably one of the fuel pumps.

My question is this thing was built before ethanol. Now ethanol is in everything. To make this motor dependable what should I update? I'm going to rebuild the fuel pump with a kit. How much more do I need to do? Fuel lines? I don't want to get stuck somewhere. I've tried 89 octane, 91 octane, and 93 octane and no real difference.

Thanks in advance for any and all advice.

 

[cheapNdisgusting]

Forgot to mention I use sta-bil, and my carbs are the internal fuel pump kind with the round bowl on the bottom.

 

[Bubbakat]

Rebuild the fuel pump and replace all fuel lines. Keep on with the stabil green or sea foam. That is about all you can do for it. Use a good plug. I have found that a surface gap NGK plug works good in those merc 50

 

[cheapNdisgusting]

Thanks, I appreciate it.