1963 Evinrude 75HP Low Speed Jet Carb Adjustment

[candiaoh]

Symptom: While at idle or low speed, the engine "surges" off and on, as if it is moving between 2 and 4 cylinders kicking in. A quick acceleration typically results in a stall. Once at high speed/WOT, runs like a champ. Decrease speed to idle from WOT and runs rough and needs a little choke to accelerate again.

I do not want to break the carb down due to lack of parts availability, gaskets, etc. I've run a Seafoam mixed in with my fuel mixture twice. I typically run at 40:1. Due to its age a little extra lubricant just means more frequent spark plug changes.

Changed last season: Coil, Points, Condenser, Fuel Line, Spark Plugs. I've a strong spark to all four plugs.

I've read some strings on adjusting the carbs. I know it needs to be in the water, in gear, choke off. Does clockwise give more or less fuel? Do both knobs adjust in the same direction?

 

[Crosbyman]

needles are like faucets.... CCW left is more CW right is less fuel

 

[racerone]

Why do you say parts availability is a problem ?---Where have you looked for parts ?----Smooth surging is usually fuel related.----Perhaps test run with another tank and hose.----Check o-rings in fuel connecters.--Check / install fuel pump repair kit.---High speed jets confirmed clean ?-----Thermostat in place ?---Throttle plates opening at the right time.-Plugs do not foul these days , unless there is an issue with the motor.----40:1 does not foul plugs any more than 50:1 mix.----All suggestions for you to study , look into.

 

[candiaoh]

Thanks guys for your input! I was think about trying another tank. The one on board now is home made thing the PO installed 20 years ago. He ran it on Lake Erie and wanted lots of fuel capacity.

 

[oldboat1]

Seafoam won't cure bad fuel in the tank. Switch to a portable tank with new line/pump/connectors -- or borrow a known good one. Empty old gas. Fill with a gal or two of fresh gas for testing. 2.56 oz 2-cycle per gallon.

 

[candiaoh]

While do my low speed carb adjustment I noticed something interesting. The "surge" that I spoke is always precipitated by a volume of water exiting the exhaust hole. So it appears that the "surge" is caused by the opening of the thermostat. Is this addressable at all?