Johnson 115 running @ 4500 rpms @ wot .help.

[Maxum21]

Took my "new to me" boat out today for the first time. Seemed to run good, idled good, got on plane decently, but from 3/4 throttle to wot it wouldnt advance past 4500 rpm's. actually from 3/4 to full thottle it hardly did anything but gain a mph. Seemed very sluggish in that throttle range. Boat is a '98 18' Larson weighing in @ 1650 lbs and the motor is a '96 johnson 115. I ran it w/ 3 other friends aboard. My prop is a ss 13.25x19 in decent shape.no gouges/badly bent blades or anything. i was told that prop should be in the ballpark for this motor. With 4 people on, boat ran 4500 rpms @ 35 mph with a clean hull(no bottom paint) but i'm off about a 1000 rpms. Where should i go from here? start messing with props or look at the motor first? thankyou!!

 

[bob johnson]

Re: Johnson 115 running @ 4500 rpms @ wot .help.

you are way over propped......try a 15, or at least a 17...but my guess is a 15 pitch...13-3/4" X15 stainless steel prop should get you more rpm which will also get you more speed.....you got a lot of boat there for a 115 pitched at 19....

you want to run that motor at 5800 rpms...... 4 people is a load!!!

bob

 

[Maxum21]

Re: Johnson 115 running @ 4500 rpms @ wot .help.

thanks Bob, the boat is rated for 9 people, so i didnt think much about my 3 passangers. But your right, i guess for a 115 it is quite a load. The boat is rated for a 150hp, but i see alot of them with the 115's so they must do alright. My next prop is going to be aluminum, so should i still try the 13-3/4"x 15"? also forgot to mention, at wot the motor started to cut-out/drop rpms. Almost like it was starving for fuel. Just put in new fuel lines, water seperator, primer bulb. Anything specific i should be lookin at?

 

[Solittle]

Re: Johnson 115 running @ 4500 rpms @ wot .help.

See if you can borrow a 17" before you buy a new prop. Post back so we can see if Bob nailed it at 15" or my guess at 17".

 

[arthurj12]

Re: Johnson 115 running @ 4500 rpms @ wot .help.

pump your primer bulb when ur at wot see if fuel pump is keeping up worth a try

 

[Maxum21]

Re: Johnson 115 running @ 4500 rpms @ wot .help.

thanks for the tip arthurj. thats a good idea and will give it a shot.
solittle: i will updated posts after trying out props.
if i'm running 35mph @ 4500 wot, how fast should i be running when i'm propped right @5800 rpm's? boat is 1625lbs according to nada

 

[bob johnson]

Re: Johnson 115 running @ 4500 rpms @ wot .help.

thanks for the tip arthurj. thats a good idea and will give it a shot.
solittle: i will updated posts after trying out props.
if i'm running 35mph @ 4500 wot, how fast should i be running when i'm propped right @5800 rpm's? boat is 1625lbs according to nada

well the motor cutting out is a whole new piece of the puzzle....you need to have the motor runnign smooth before you can figure what prop...

if you go to aluminum and your motor is currently running ok..id say you will need a 13 pitch with that load you were carrying in that boat .

in SS you might not have to go lower than 15....do you ski or pull tubers at all????
if so...you REALLY want to be running 5800 alone in the boat......you have a range..and you are at the bottom....you will carbon up your motor if you are set up to only turn 4500 at WOT.....

plus you really dont know how much the boat weighs....weigh it on the trailer on day at a junk yard that buys scrap....its always a great idea to actually KNOW what your rig weighs... you can probably guess or look up what the trailer would weigh alone.

id go ahead and rebuild the carbs...to make sure you dont have any debris in the high speed orifices or passages...

you dont know how long it has been since the carbs were rebuilt....

there maybe be other issues causeing the stumble at WOT that are electrical in nature....

for th same pitch..a SS prop will trun more rpms usually than an aluminum one

bob

 

[Maxum21]

Re: Johnson 115 running @ 4500 rpms @ wot .help.

Bob, previous owner said he had carbs rebuilt this past year. After some reading & searching i think i have a fuel related problem, either at the fuel pickup in the tank or possibly a weak pump. The pump is a non oil injecting basic omc pump. Anyway to test the suction with a meter or something? I noticed at one point yesterday i hit a series of waves and thats when i noticed the motor cut out at wot. Brought it back down to idle and powered it up again and it seemed fine. It stalled out twice at wot. other than that it seemed to run really smooth. Maybe debris in tank blocking the fuel pickup filter? I am running premix xd-50 synthetic blend oil. Could that be causing any issues(i doubt it would be) but cant seem to find a clear cut answer whether or not its ok to use for premix as opposed to strictly oil injection. Bottle doesnt specify whether or not it can be used for premix but marina told me it can. as far as the prop i think i'm going to try aluminum first. i will give the 13 pitch a shot like you said and take it from there. i dont do any skiing but will be doing some tubing on average with 4 people onboard. Weight of boat according to nada, and iboats specs is 1625lbs. Not sure if thats including the motor or not?

 

[bob johnson]

Re: Johnson 115 running @ 4500 rpms @ wot .help.

Bob, previous owner said he had carbs rebuilt this past year. After some reading & searching i think i have a fuel related problem, either at the fuel pickup in the tank or possibly a weak pump. The pump is a non oil injecting basic omc pump. Anyway to test the suction with a meter or something? I noticed at one point yesterday i hit a series of waves and thats when i noticed the motor cut out at wot. Brought it back down to idle and powered it up again and it seemed fine. It stalled out twice at wot. other than that it seemed to run really smooth. Maybe debris in tank blocking the fuel pickup filter? I am running premix xd-50 synthetic blend oil. Could that be causing any issues(i doubt it would be) but cant seem to find a clear cut answer whether or not its ok to use for premix as opposed to strictly oil injection. Bottle doesnt specify whether or not it can be used for premix but marina told me it can. as far as the prop i think i'm going to try aluminum first. i will give the 13 pitch a shot like you said and take it from there. i dont do any skiing but will be doing some tubing on average with 4 people onboard. Weight of boat according to nada, and iboats specs is 1625lbs. Not sure if thats including the motor or not?

nada weight is suspect...dont trust them...but in any case it does not inclue that 320 lb motor!!!

is your motor an ocean runner or an ocean pro??

or is it a 115 special?

sure it could be debris in the pick up or a weak fuel pump that cant keep up with WOT needs....but that should be consistant...your inconsistant problem suggest, electrical heat influenced parts or fuel pick/tank issues.

so your tests shuld be considered ok when you thuink the motor is running fine at WOT....

what is the MODEL number of your motor?

or do you have a picture of it?

PS : id start with a 15 pitch first...they usually will take it back if itsnt the right one as long as you take a different

bob

 

[Maxum21]

Re: Johnson 115 running @ 4500 rpms @ wot .help.

i'm not sure what model it is. i do know it 'was' fuel injected at one time but the oil/fuel pump was removed and has been premixed since. ive attached a few pics below. the second pic is of the fuel pump. the fuel line that ran from the bottom of the fuel pump to the bottom of the plastic tubing(that then feeds the carbs) had a major kink in it. as you can see it has to make a sharp bend. i'm going to replace the kinked line with a more flexible, softer line.i'm not sure if that was my problem or not, but the kink was bad and could have easily been restricting fuel flow. what do you think?
i will start with the 15 pitch and let you know how it works out.

 

[bob johnson]

Re: Johnson 115 running @ 4500 rpms @ wot .help.

absolutely the kinked fuel line could restrict fuel flow...that would be such and easy fix

you have a J115TLEDA, unless you have an extra long gearcase which would be a J115 TXADA( dont know why they put the first A in that model number as it doesnt match the strandard model number pattern

good luck

bob

 

[Maxum21]

Re: Johnson 115 running @ 4500 rpms @ wot .help.

thanks Bob. i replaced the kinked fuel line with new and put in a new 'see-through' inline fuel filter. I primed the bulb, fired it up and let it idle a few minutes and noticed that the filter was near empty after a few min of idling. there was still a dribble of fuel still entering the filter, but most of the fuel was gone.i primed bulb again and filter was 90% full of fuel, but again same thing a few min later it was near empty. is this normal?
btw sorry for all the questions