Johnson 25 Prop size

[Tdunne96]

Good day everyone, I am currently troubleshooting low top speed and unable to get on plane with my Lowe Angler 140S 14’ side console aluminum boat. Has a Johnson 25hp long shaft engine which is the factory set up from the dealer. Currently has an aftermarket 10.3x12 3 blade unbranded prop on it and the engine rpm’s seem low when on the water. That size isn’t even in the factory parts manual. I assume I need to go lower and my options for factory are 10.5x11 and 11x9. Looking for any advice here as I have no clue what size the boat came with. The engine model is J25ELSOB 2005 model.

 

[racerone]

Doubt it is a prop issue.----Trouble shoot the motor.-----Might be running on 1 cylinder.----Post actual compression numbers.----Does spark jump a gap of 3/8" on both leads ?

 

[Tdunne96]

Doubt it is a prop issue.----Trouble shoot the motor.-----Might be running on 1 cylinder.----Post actual compression numbers.----Does spark jump a gap of 3/8" on both leads ?

I will do a compression test and check spark when I take it back out after it stops raining. I was only thinking prop issue because it runs great and revs up fine outside of the water. Bought from a local dealer and obviously they said they went through the motor and everything tested great.

 

[racerone]

It will rev up fine on a hose when running on one cylinder.----Take it back and insist they check it over.

 

[flashback]

Might try it without the whale tail.

 

[airshot]

Just based on the pic, it looks like the motor is trimmed in to far. Do you have a tach for the motor ? Whale tails are a last resort only for boats not trimmed out or balanced load weight

 

[Tdunne96]

Just based on the pic, it looks like the motor is trimmed in to far. Do you have a tach for the motor ? Whale tails are a last resort only for boats not trimmed out or balanced load weight

I have a tach on the way. The current trim gives me the highest speed and best ride. I’ve tried every position. I will remove the tail and test next time I go out. I believe it was the previous owners attempt at trying to get it to plane out rather than find the source issue.

 

[racerone]

Boat should run near 25 m/hr.-----Maje sure there is a new water pump impeller installed too.

 

[Tdunne96]

Boat should run near 25 m/hr.-----Maje sure there is a new water pump impeller installed too.

That is about what I expected 20-25. I get about 15-17 tops at the moment with only me on the boat. Supposed to clear up this weekend I will run a compression test on both cylinders and check spark. Also plan to clean out the jets on the carb. Once that is done I will lift the motor up onto the higher setting so the cavitation plate is closer to the bottom of the transom. I will then take it out and check rpms with a tach.

 

[airshot]

On initial setup I always trim the motor so the cav plate is parallel to the bottom of the boat using a long straight edge. Put it up against the bottom and adjust trim until the cav plate and hull are parallel. Now...is the cav plate above or below the bottom of the boat? Within a 1/2" either way is normal. Hook up your tech and make test run. How loaded is your boat weight wise ? With one person and safety gear you should be around 25 mph, use a GPS to measure speed. Check your motor operation first, you may have an engine issue !