1971evinrude18hp runs 'extremely' rough

[jaws06]

Engine runs fine at idle and full throttle-planing speed. Problem is getting to full speed. Engine sputters and bucks for about 30-60 seconds until on plane and then runs fine. I've changed the plugs ,points and condensors so far. Anyone have any ideas on what else I can try?

 

[samo_ott]

Re: 1971evinrude18hp runs 'extremely' rough

Is the boat too heavy? Or loaded poorly? Is the high end speed normal once you get to it? It sounds like it's happening under load. Can you post a video?

 

[jaws06]

Re: 1971evinrude18hp runs 'extremely' rough

The boat is a 16ft aluminum mirrocraft. I believe it is a little underpowered because the previous owner of the boat had a 25hp on it. This motor was given to me for nothing. I've been on underpowered boats before, but never seen a motor react like this. Also cant tell if it only happens under a load because it spits the water out of the barrel too fast. cant post a video now,maybe in near future.

 

[jaws06]

Re: 1971evinrude18hp runs 'extremely' rough

High end speed is a little slow but it still planes out then runs perfect