1983 evinrude 90hp

I just bought this 1983 evinrude 90hp from a guy on craigslist it runs fine but sometimes sputters. I have good gas and rebuilt carbs. When it is idling in runs great then it idles real slow and sometimes cuts off, it surges up and down like someone was revving the throttle. Can someone help me with this?

Check the throttle butterfly linkage between the carburetors as follows....

Back the throttle off so that the scribe mark on the metal cam DOES NOT touch the throttle cam roller of the carburetors.

Remove the carburetor plastic face plate so that you can observe the throttle butterflies as well as the outside linkage connections.

Adjust that vertical throttle butterfly connection rod that links the two carburetors so that both butterflies start to open at the same time... and also close completely and open fully at the same time. You DO NOT want one butterfly closed and the other ever so slightly open or the condition you state will take place.

Now, adjust the sync so that the scribe mark on the cam aligns dead center with the throttle roller when the throttle butterflies just start to open.

Did this cure your problem?

Yeah buddy! That fixed the problem. Thank you once again.

Good for you... Happy boating.

Deep in my mind............ (Yea, finally fixed one!)