1972 evinrude 50

Hello I have two questions,#1 my motor seems to be working good until the throttle is in wide open
position it gets up on plane and go's for a short distance and then begins to surge reving up and
down if I pull the throttle back to 3/4 position it works just fine. should I look at the fuel pump or
remove the carbs and inspect the high speed jets to see if there plugged?
#2 being this is a older motor should I mix the gas at 50/1 or play it safe at 40/1??????????

thank you John

First check that you have spark on all cylinders and that it is a blue fire, also check compression.Or sounds like yo need to adjust the air flow to your carbs,should be a screw on carbs for adjustment.If that dont work then yes i would rebuild carbs.That old of an engine see owner manual for fuel mixture on that year model.If you mix it with to much oil it will not run the same.im just not sure on mixture on an engine that old.

Hello I just removed carbs and they are in good shape very clean in side the only thing was the slow speed jets
were set at top carb 1/2 turn off seat and the bottom carb was 1 turn off seat so I set them both at 1 turn out,
as the sticker under the hood says 3/4 turn to start and then adjust as needed,next to do is the fuel pump as I
suspect it might not be keeping up with the demand.only other thing I can think of is it might be electrical (I hope not )

As far as the over-reving goes, it sounds like you have a spun prop. As you are putting max power on it, the rubber shaft holder is spinning inside the metal hub. It is very difficult to see, but remove your prop and look for tears along the edge where the rubber attaches to the metal hub. You can test it by using some paint or marking tool to mark a line where the rubber and hub match up, re-install the prop and take it for a spin until it over rev's, then remove the prop and see if the marks are still lined up. If not, then you will need to get a new prop or have that one re-furbished.

As for playing with the oil mixture. If I recall correctly the specs for any Evinrude built after about 1964 calls for 50:1. If you have a lot of hours on the motor, or you use it alot at WOT, then it seems that 40:1 would help preserve the rings and give a better seal. BTW - you should run that engine at WOT whenever it is safe to do so in order to burn out the carbon build up and keep a good seal on the rings.

Follow up. Next time you have an issue with this engine, you should post your question on the Johnson/Evinrude forum on this site. There are more folks with more experience with these engines on that forum.