1999 Johnson 25HP - Power/Planing issue

[jbjennings]

Re: 1999 Johnson 25HP - Power/Planing issue

I'm unsure which diagram you're referring to as to part #4. Which page? Carburetor?

Also, you have a tach on a 25hp? What is it, a tiny tach??
You may have a prop that's not the right pitch. If it's getting 4500 rpm's, I'd think it's getting spark on both cylinders. It should get about 5300 rpms at WOT, I'd think.
Last of all, your carb in the pic looks a lot different from mine, which is a '99 johnson 30hp. Mine doesn't have electric start or electric choke, so maybe since yours does it has a totally different carb.
Sorry I can't be more helpful,
JBJ

 

[Pecenje]

Re: 1999 Johnson 25HP - Power/Planing issue

My boat has a console and it has a tach on it... tach is a 7K Amega series (teleflex) on the 5P setting

my carb doesn't have a choke, only the primer?

#4 in this picture

 

[aerobat]

Re: 1999 Johnson 25HP - Power/Planing issue

what is the weight of the boat and how many persons on board during the test? maybe you do not have any problem with the engine but 25 hp are simply not enough to get on plane with this boat. getting 4500 at WOT sounds to me that both cylinders work but the boat struggels against the high resistance before planing the boat out.

 

[Pecenje]

Re: 1999 Johnson 25HP - Power/Planing issue

never weighed the boat...

16.5 foot aluminum with a side console...
3 batteries
2 people on board

thing is i get 5mph out of my 1 cylinder 4hp motor...

doesn't seem right that with 6x more motor (25HP) i'm only getting 11mph

 

[Cofe]

Re: 1999 Johnson 25HP - Power/Planing issue

Have you rebuilt your carb yet? I noticed in your motor pic that #1 has mix running out of it. I would find a single strand of copper electric wire and make sure Jets # 1 and your high speed jet #22 are not gummed up. #22 jet sits behind that flat blade screwdriver plug on the front bottom of the carb bowl. You can remove that plug and carefully poke through it with the copper wire while the carb is still attached to the motor.
Nice rig by the way......

 

[restornator]

Re: 1999 Johnson 25HP - Power/Planing issue

the boat is displacing too much water, that's why you see little speed difference with 21+ Hp. You need to check the flotation foam and make sure it's not saturated. It's not the motor, it's the boat weight/underpower.

 

[Cofe]

Re: 1999 Johnson 25HP - Power/Planing issue

You should get higher RPM's
Try this....with motor off, put controll into forward WOT.......then check the butterfly in the carb. It should be wide open and not tilted any.

 

[wmconway]

Re: 1999 Johnson 25HP - Power/Planing issue

Sounds like you might be a bit underpowered. Check the horsepower and weight load ratings for your boat. You might try unloading some weight and see if you can get it to plane. Have you noticed any cavitation while running full throttle?

 

[Pecenje]

Re: 1999 Johnson 25HP - Power/Planing issue

The boat is rated for a 50...
25 yes is underpowered, but it's all i can afford right now...

the boat is not water logged, i had the bow area opened up for re-riverting and checked it while it was open...
all the foam is dry...

the pic posted is an old pic... there it had a 20 suzuki tiller and a 4.5 evinrude
now it has the 25 johnson and a 4hp 4stroke yammy on it...

No way of removing any weight really... it's a fishing boat, and i need all the stuff in it...
2 of the batteries for the bowmount are under the side console and the other is in the port stern

I have not rebuilt the carb yet... i'm trying to find time for that

 

[Pecenje]

Re: 1999 Johnson 25HP - Power/Planing issue

Have you rebuilt your carb yet? I noticed in your motor pic that #1 has mix running out of it. I would find a single strand of copper electric wire and make sure Jets # 1 and your high speed jet #22 are not gummed up. #22 jet sits behind that flat blade screwdriver plug on the front bottom of the carb bowl. You can remove that plug and carefully poke through it with the copper wire while the carb is still attached to the motor.
Nice rig by the way......

no carb rebuild yet...
for #1 do i unscrew it and have at it? or how would i clean it?
same with #22 after i pull the plug out of it?

it is a good fishing boat...

 

[Cofe]

Re: 1999 Johnson 25HP - Power/Planing issue

Just leave them in place to clean them. Use the copper wire, and maybe a shot of aerosol carb cleaner.

 

[aerobat]

Re: 1999 Johnson 25HP - Power/Planing issue

never weighed the boat...

16.5 foot aluminum with a side console...
3 batteries
2 people on board

thing is i get 5mph out of my 1 cylinder 4hp motor...

doesn't seem right that with 6x more motor (25HP) i'm only getting 11mph

that seems right. before you get on plane the water resistance explodes above hull speed without gaining speed. the engine has to push the boat above the top and plane it out to reach a significant higher speed. your 4hp pushes the boat in displacement ride with low resistance and the 25 hp is not able to push it over the top to plane - so uses its more power mostly in raising the bow and now gaining much more speed. thats a pretty normal situation. the too low rpm at WOT also seems right since the engine surely is stock proped for a smaller boat than yours

i would be careful in repairing an in my opinion good but to little engine. with three batteries, two persons and a 16.5 ft aluminium boat you should look for a 40hp and sell your 25 to get the pleasure you expect.

 

[Pecenje]

Re: 1999 Johnson 25HP - Power/Planing issue

Ok, i did the spark jump test and it passed at 7/16" so spark is good...

I also rebuilt the carburetor, also removed the 2 welch plugs (1 on top and 1 in the float chamber) and cleaned out there...
cleared the jets, the only thing i didn't take apart was the needle valve... i did remove #11-14 as an assembly and changed O-ring #10
but did not open and diss-assemble 12, 13, 14

motor fired up good after everything was set and done... I plan on doing a water test tomorrow to see if it makes a difference (fingers crossed)

the welch plugs have a huge gap under them... Unless you smash it with a sledge hammer, there was no chance of damaging underneath it by any means... (atleast with my carb)

I'll post tomorrow after the water test

 

[wilde1j]

Re: 1999 Johnson 25HP - Power/Planing issue

If you can't get the boat on plane, the HP doesn't make much difference, BC you're only going to get hull speed (~ 8 to 9 knots) for most typical boats. Clearly, your boat is not getting on plane. A lower pitch prop that could get RPMs up to say 5500 might do the trick, otherwise a bigger motor is going to be needed. Sounds like the motor was fine all along. Shame you spent time on rebuilding, etc. when setup was the issue, not engine tuning.

 

[Pecenje]

Re: 1999 Johnson 25HP - Power/Planing issue

Took the boat out yesterday for a water trial and do some fishing...

also ended up taking out the 2 trolling motor batteries cause one is pooched...

boat was able to get up on plane (took a while, but it did)
managed to hit 19mph (took a while)
it got up to 12mph (4600rpm) then slowly bit by bit started increasing speed and rpm (i didn't give additional throttle)
i'd say it took about 2 or 3 minutes to get from 12mph to 19mph

also at 19mph the rpms got up to 5400rpm?

not sure why the rpms wouldn't increase right away at full throttle

played around with the tilt pin setting too...

any ideas? about the increase in rpm and why it would take so long to get on plane?

 

[Pecenje]

Re: 1999 Johnson 25HP - Power/Planing issue

also noticed this when rebuilding the carb...

the thing in the middle of the float chamber is not in the center? (not sure what it's called, but you can see it clearly in the pic...

 

[Tim Frank]

Re: 1999 Johnson 25HP - Power/Planing issue

Took the boat out yesterday for a water trial and do some fishing...

also ended up taking out the 2 trolling motor batteries cause one is pooched...

boat was able to get up on plane (took a while, but it did)
managed to hit 19mph (took a while)
it got up to 12mph (4600rpm) then slowly bit by bit started increasing speed and rpm (i didn't give additional throttle)
i'd say it took about 2 or 3 minutes to get from 12mph to 19mph

also at 19mph the rpms got up to 5400rpm?

not sure why the rpms wouldn't increase right away at full throttle

played around with the tilt pin setting too...

any ideas? about the increase in rpm and why it would take so long to get on plane?

Everything that you just posted confirms what everyone has already told you.

Your boat, with that motor, and that load and weight distribution is performing exactly as it should.
If it is not what you can accept, you have to re-power.

The RPM increase is also exactly what would be expected.

 

[wilde1j]

Re: 1999 Johnson 25HP - Power/Planing issue

Simply put, as pointed out above, motor is too small.

 

[Pecenje]

Re: 1999 Johnson 25HP - Power/Planing issue

if this is normal behavior for a boat that is under powered then okay...
( I've just never experienced this before... cause my boats were not under powered )

for the time being, i can't afford a bigger motor...
and this one will have to do...

 

[AlTn]

Re: 1999 Johnson 25HP - Power/Planing issue

that's the venturi tube < not sure that's the proper name > it's in the right position