1975 Evinrude 15hp throttle adjustment?

[Seawolf_504]

I have a 15hp Evinrude on a 14' fiberglass fishing boat. I recently got the boat from my Dad to use on the flats around where I live. After doing a carb rebuild it runs really well and cranks up on the first pull every time, but I am having a problem getting up on a plane with me and my Wife in the boat.

I weigh around 250lbs and my Wife is around 130lbs. When I go to open up the throttle to full the RPM run right up no problem and it sounds like it is at full throttle, but it can't quite get on a plane. If I play around with the choke and pull it out about an inch or two the motor seems to jump up a notch in RPM and it's usually enough to get up on the plane.

I've already rebuilt the carb, changed out the coils, replaced the plugs and even got a brand new fuel tank, fuel lines, and placed a filter on the line coming from the tank.

Now my Dad said he always just used regular unleaded (87 octane), but I was thinking maybe throwing some higher octane in there to see what happens. Is using 93 octane ok for older 2 stroke engines?
If not changing the fuel does anyone have any experience with adjusting the throttle on these and should I get more power from this motor?

I'm a big guy and I know weight has a lot to do with it, but I have seen this motor get up on a plane no problem with me and my Wife in it, but it takes playing around with the choke to do it.

Any help would be appreciated.

 

[AlTn]

Re: 1975 Evinrude 15hp throttle adjustment?

sounds like classic lean condition at high speed...the orfice plug in the carb must be spotless and the float level parallel with the carb body when inverted...the carb roller should be ~ centered on the timing cam mark when the throttle plate is just beginning to open;then this plate should be horizontal in the carb throat when the throttle is fully advanced and the roller at its highest position on the timing cam....shop2.evinrude.com will have the carb diagrams for your motor

 

[Seawolf_504]

Re: 1975 Evinrude 15hp throttle adjustment?

Are you talking about the roller cam that contacts the red bar when you twist the throttle? I checked that tonight and adjusted it out. Will see if that made a difference.

 

[AlTn]

Re: 1975 Evinrude 15hp throttle adjustment?

go to shop2.evinrude.com...find your year and model..go to carb&manifold diagram..part no. 34 is the carb roller..it rest against part no.37 in the magneto diagram..as you twist the throttle handle part no.37 moves with the armature plate as it is attached to it...as this timing cam moves, so does the carb roller...it rides on the cam and links the advancement of the timing with the opening of the carb plate <butterfly>...this increases air/fuel flow in the proper proportion to ignition timing...the first post gives the starting position on the timing cam for the roller...and the position the roller and timing cam should be in at wot < wide open throttle >...you'll see the mark on the timing cam..just adjust so that the carb butterfly is beginning to open when the roller is against this mark...gear selector in neutral...