1965 mercury 9.8 hp idle issues

[Ted Riley]

Here’s what I have done thus far.... cleaned a plastic fuel tank made sure the vent is proper. New fuel lines including inside the engine cowl. New primer bulb.New fuel pump diaphragm. Rebuild carburetor. Installed new points and gapped them at 30k.runs fine at high idle or starting position and in neutral. Lower the idle a little and it spits and sputters then dies. I hate giving up on this girl, but I’m close to it. Any help would be greatly appreciated. Thank you

 

[RCO]

Points gap on that motor is .020, not .030. Carb completely disassembled and cleaned? Is it running in a barrel or on the back of a boat?

 

[Ted Riley]

Yes to the carburetor. Ran engine both ways. After rebuilding the carb and new points. It ran nice in a tank.low idle just perfect I thought.But I noticed a gas leak in one of my fuel pump lines. So I decided to replace both hoses off of the fuel pump and that’s when things changed. I could not find the pre-fabricated hoses so I had to make my own. i used 3/16 ID fuel line for the fuel pump.I put a new primer bulb on correctly.Now the engine will start and will run fine at high idle when I lower the idle it starts to spit and sputter and eventually dies.

 

[Ted Riley]

Would increasing the fuel lines to and from the fuel pump help? Like a 1/4” ID?