Boat won't hold speed

[Dersu Uzala]

I have a 1988 Sunbird 170 with a 88 hp Evinrude. It is impossible to hold a steady speed. When it slows down and I increase the throttle slightly, it holds the speed for 10 seconds or so then the boat keeps speeding up. When I slightly decrease the throttle, it is fine for 10 seconds or so, then gradually keeps slowing down. I can't get it to hold a speed. Any ideas?

 

[alldodge]

Speeds up until its slowed down then starts slowing down

Don't see this as a control issue, most likely a motor/carb issue

 

[Bondo]

Ayuh,...... Welcome Aboard,...... At 'bout what speeds is this happenin',..??..??

If it's as it breaks over onto plane, it could be that ya just gotta go alittle faster, or alittle slower,.....

 

[Scott Danforth]

agreed, if this is in the window from just getting on plane to just under cruise (about 15mph to 24mph depending on the hull planing speed of your boat), you may not be able to

 

[Dersu Uzala]

I am usually trying to hold the speed at 18-20 mph. Its slips to as low as 14 and as high as 25.

 

[Scott Danforth]

your boat probably wont plane at the 18-20 without trim tabs. it slips as low as 14 because you fall back in the hole.

try holding 23-25