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 !

 

[jimmbo]

Also plan to clean out the jets on the carb.

The may entail removal of the Carb, which then a check and possible adjustment known as a Link and Sync, will likely be in order

However, have you verified that the Carb is opening Fully when the Throttle is mashed? In order to do that, You will need to put the motor into forward, but you will need to do that with either the Flywheel or the Prop rotating

When it comes to Engine Height, Normally the Rule of Thumb is Flush with the Hull, However on a Tin Boat, there is often a Protruding Keel running down the center of the Keel, and that can affect at what height the Engine needs to be mounted

 

[Tdunne96]

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

Have new water pump kit, carb gasket kit, and oem prop on the way. 135 top and 130 bottom for compression. Both cylinders confirmed good spark and firing. Only thing I noticed is boat will run on just bottom cylinder but not top cylinder. But both cylinders do fire when both wires are hooked up. Had to drill, tap and helicoil the bottom cylinder as the plug was cross threaded in place. This dealers handiwork is top notch I would say lol. I bought the boat as-is so it is what it is I’m not paying them another dime.

 

[Tdunne96]

The may entail removal of the Carb, which then a check and possible adjustment known as a Link and Sync, will likely be in order

However, have you verified that the Carb is opening Fully when the Throttle is mashed? In order to do that, You will need to put the motor into forward, but you will need to do that with either the Flywheel or the Prop rotating

When it comes to Engine Height, Normally the Rule of Thumb is Flush with the Hull, However on a Tin Boat, there is often a Protruding Keel running down the center of the Keel, and that can affect at what height the Engine needs to be mounted

When throttle is fully forward, the throttle linkage does max out but the throttle plate I can manually open a miniscule amount more by hand. I plan to do a full carb rebuild and clean with adjustment. As far as engine height, I have 2 sets of holes for adjustment. Other pictures of my boat online with the same motor are on the higher adjustment where mine is on the lower one. I plan to move it back up to the factory setting when I do the impeller. Hoping this all helps.

 

[racerone]

Need to determine issue with top cylinder.----Fuel pump diaphragm ruptured??----Reed valve issue?

 

[Texasmark]

I totally agree with what's shown in the picture as potentially being your problem. Let's assume that the mechanic that tested the engine did a thorough job and it runs fine. Let's say that the prop is original. Let's say that you have fresh 50:1 gas-oil mix in your fuel tank.

As "Airshot" mentioned, the engine it tucked in too far toward the transom and especially with the Whale's tail, just drives the bow of the boat down and into the water. This does 2 things: Increased drag severely limiting top end and loading the engine thus reducing RPMs and speed, and second, it makes steering cumbersome.

At speed (say 25-35 MPH) the bow (front of the boat) is supposed to be up at 15ish degrees above the surface of the water. The boat should be easy to steer, very responsive to engine direction. Spray should be strong and small droplets/mist. Engine should be heard running at a high, solid, RPM. With the tail and tilt position you currently show, none of that should be occurring.

So take the cheap, easy way out.......move your tilt pin out 2-3 holes away from the transom. Take the boat out and test it. Adjust the pin out one more slot and test it. Move it back in 1 slot closer than when you just started testing it and test it again.

If that solves your problem, find the sweet spot in the tilt position and go out and have fun. If it doesn't then get out your wallet, wrenches, and spare time and go after the problem.......and when you get all that done, move your tilt pin out when you get the engine running properly.

Good Luck.

 

[jimmbo]

Add a leaky Crankshaft Seal to the List of things that can cause Issues with the upper Cylinder