40 hp 1966 Evinrude full speed problems

[Squaresailor]

My 1966 40 hp Evinrude Lark will run well up to about 3/4 throttle, then dies. Checked the fuel bulb and is still pressured. Starts again no problems. I noticed the slow speed idle adjust is loose but that should not affect high speed. Non adjustable high speed jet. Any ideas?

 

[racerone]

A very good motor , worked on lots of them.----I can not see , feel or hear your motor.-----So post your compression test values.-----And does spark jump a gap of 1/4" or better on a test device, yes or no ?-----Sounds to me that it might be running on 1 cylinder.-----Have you had the flywheel off for inspection ?-----How did it run for you last year?

 

[oldboat1]

There's a jam nut at the low speed needle -- snug that up so the needle can be adjusted, but doesn't flop around with engine vibrations.

Try running with the choke on the manual setting, in case that is an issue.

 

[Squaresailor]

Tha

There's a jam nut at the low speed needle -- snug that up so the needle can be adjusted, but doesn't flop around with engine vibrations.

Try running with the choke on the manual setting, in case that is an issue.

Thanks. Will try

 

[Squaresailor]

A very good motor , worked on lots of them.----I can not see , feel or hear your motor.-----So post your compression test values.-----And does spark jump a gap of 1/4" or better on a test device, yes or no ?-----Sounds to me that it might be running on 1 cylinder.-----Have you had the flywheel off for inspection ?-----How did it run for you last year?

I only just bought the motor so I have no history. It runs so smoothly I would not suspect a single cylinder problem. I assume the only way to check would be to pull plugs and see if one is wet?
Also can you help me out by letting me know what I might look for if I pulled the flywheel. Thanks

 

[racerone]

Oh well----Most folks start on these motors by cleaning the carburetor.----So give that a try.-----If that does not get the results you are hoping for then take a stab at something else.---I think there are many tutorial videos on u-tube that cover this popular series of motors.--------Sorry.

 

[Squaresailor]

I did a clean before it went in the water, but I will recheck. Thanks.

 

[racerone]

Your motor needs certain things to run correctly.----It has 2 ignition systems ( one for each cylinder )-----It needs fuel and not too much fuel.----Spark at the right time.----Compression in the cylinder.-----Compression in the crankcase.----Correct propeller fitted to match the type boat you have.