Evinrude 1961 10HP won't idle

[takitaki]

Hello everyone,

I have recently finished restoring a 10HP, which included rebuilding the carb, water pump, replacing the thermostat and lower unit service.

While testing it on a tank, it runs good, but won't low rpm idle. I tried to adjust the jets (started with 1-1/4 low speed, 3/4 high speed), and the response to the adjustments was erratic - sometimes it would run better with the low speed jet completely seated, and sometimes opening it to 2-1/2 turns would still behave like it was lean.

Both cylinders firing - the motor would run on both of them separately. No air leaks as far as I can tell.

Edit: verified that the throttle timing is set correctly.


I'm attaching a video below as an example. Would appreciate your comments.

 

[racerone]

Make sure throttle plate is closed at idle.----Open low speed mixture screw 1/8th turn at a rime.----Likely the classic low speed sneeze will go away.

 

[takitaki]

Make sure throttle plate is closed at idle.----Open low speed mixture screw 1/8th turn at a rime.----Likely the classic low speed sneeze will go away.

After all the usual remedies didn't work, and the motor still refused to idle and ran like it had an air leak, I took a closer look at the carburetor and discovered that the top welch plug got blown out somehow, and was just laying upside down on top of the cavity, so I didn't see the problem at first. That would explain the erratic behavior and an uncontrolled air leak. Re-seated and sealed with some permatex #3.

All good now:

 

[takitaki]

UPDATE: might be useful to some - idle continued to be choppy and unstable, no amount of adjustment helped. Otherwise run great, WOT with plenty of power. I decided to go into the carb, and discovered that the orange rubber bowl gasket got swollen, probably from over-tightening the screws and/or gasoline and was partially blocking the idle passage. Replacing the gasket with a regular non-rubber gasket solved the problem.