1977 18' Ebbtide Ski Boat with Johnson 115. Top speed???

[bmax9443]

Hello everyone! Bought my first boat several weeks ago. It was sitting in a barn for the last 10 years. The old owner told me it would do 50-55 mph. I cleaned the carbs, changed the plugs, and it fired up. Took it out and it did pretty good until the throttle cable started splitting. Top speed that day was 38 mph. Then I changed the water pump assembly, changed the thermostat, got a new throttle cable, installed Boyeson power reeds, rebuilt the carbs, and added bigger jets. Took it out yesterday and again the top speed was 38 mph. Is that all I can get from this set up?

 

[mr 88]

Probably. How much does the boat weigh ? 18' boats usually have some weight to them unless there designed as a go fast set up, as in a almost flat bottom or a small 12"x 12" or so pad on the bottom of the stern that the boat rides on at speed. Did the PO use GPS or was it seat of the pants 50-55mph. What RPMS are you turning and what is the motor rated for. To get more speed you are more than likely going to have to get a jack plate,low water pick up and change props to a cleaver/raker . Changing jets is not going to give it any more speed unless its because of elevation. Without throwing a ton of money at it and making sure you don't have any water in the sub-hull [saturated foam ] I would say your tapped out. For what its worth I have a 150 hp//crank rated,not at the prop/ on a 15' tunnel hull boat that weighs about 400 lbs and rides on about the last 1" of the bottom and hits 54 mph GPS

 

[Scott Danforth]

when you rebuilt the carbs, did you perform a link-n-sync?

if your '77 is the Riviera, it weighs in at 2400# and is rated for a 175hp motor

38 may be all you get out of the boat with 115 crank rated hp.