only 3800 RPM at WOT - loss of power under load -- please HELP

[jrousell]

I have a 115 HP Johnson Outboard.

Ran great up until last week. I have replaced plugs and fuel filter. It starts up and runs very smooth. accelerates a little moer slowly than it used to and now will only get up to 3800 RPM at full wide open throttle. it does not sputter or skip or anything- it just doesn't go as fast as it should now.

It runs very smooth and sounds great all through the rmp range. It goes all the way through the rpm range when not under load of course...

I did use some carb cleaner on it and it didn't seme to have any impact at all.

What shoudl be my next thing to look at?
The
Should I try running of a small auxiliary fuel tank maybe? ( does this sound fuel related?)

VRO and power pack were both replaced last year by the previoous owner- and this ran great all spring...

This is a 1993 115 HP johnson V4 with VRO

I really relaly relaly appreciate your time and help!!!

 

[licketdsplit756]

Re: only 3800 RPM at WOT - loss of power under load -- please HELP

DONT USE CARB CLEANER. 2stroke engines you will dry out the cylinder walls. and create wear.my 115 i had to rebuild my carbs to get the performance out of it.due your basics first compression check/fuel filter/tcw3 oil in your vro.plugs/wires. make sure theres no water in the vro system.unless you have the knowledge to rebuild the carbs your self. its about 120 $ for each carb..i always run a high octane gas also. seams to help alot. ive heard run seafoam but others can explain that to you better as i have never used it. heard good things about it. BE RESPECTFULL AND LISEN BUT DONT BUY ALL THE ADVICE YOU GET.

 

[ezeke]

Re: only 3800 RPM at WOT - loss of power under load -- please HELP

Thanks JB

 

[reeldutch]

Re: only 3800 RPM at WOT - loss of power under load -- please HELP

what do you mean by it goes trough all rpm ranges not under load.

never never rev your motor up in nutral to high rpm ranges.
more than 2000 rpm in neutral is asking for problems.
and it doesnt tell you anything.
i can rev up 1 cylinder in neutral to 5000 rpm.

so now back to your problem.

you replaced the inline fuel filter or the water seperater?

first thing to do before trouble shooting is check the compression.
should be even within 15psi from highest to lowest.
if you have 3 cylinders of 115 and 1 of 100 you should be fine but might give you an indication if you have a history of equal compression.

if your compressin is fine you got to check spark.
make shure all 4 plugs are firing 7/16 gap.

the spark could also be a intermitted problem and drop a cylinder at 3800 rpm.
you could check that with a timing licht.

make shure that you link and sync is good.

last bud not least is the fuel.

since you replaced a fuel filter gives me reasons to believe there might be a fuel delivery isseu.

before you replaced the filter it was all running fine.

when you hit wot at 3800 and it doesnt get any higher hit the primer see if it picks up.
if it does its probbebly the fuel system thats will need our attention.

so do the following:

compression
spark.( spark tester)
spark intermitted test. (Timing light at wot)
fuel (hit primer at wot)

tell us what the results are and we might be able to help you further.

 

[jrousell]

Re: only 3800 RPM at WOT - loss of power under load -- please HELP

I did a compression test and they are all almost identical at about 115.

How do I do a spark test at 7/16. The gap on the sparkplugs I have right now is set to .030(owners manual spec). Do I have to make some sort of test plug with a larger gap and try and do this at night to see the spark? if I do- how do I ground the side of the spark plug for this test? ( wire clamped to the block or something? anyone have a picture or instructions?

shoudl I have the gas line disconnected and just turn it over a few times for this kidna test?


A friend-of-a-friend suggested going out on the lake at WOT and disconnecting one sparkplug wire at a time- to see if I get a further drop? and if I get no drop then I have a cylinder with an issue( posisbly ignition related) -- this sound like a good thing to try also?


I do not have a timing light( nor any idea how to use it)

I am VERY thankful for your time!

 

[iwombat]

Re: only 3800 RPM at WOT - loss of power under load -- please HELP

For the spark test you need to make or buy a spark tester (about $10 or so at the autoparts store). It's just an adjustable air gap with a clip to attach to the block - nothing fancy. 7/16" over air simulates the conditions of a spark plug in the combustion chamber during operation.

You can also make one with a board and some nails.

 

[ezeke]

Re: only 3800 RPM at WOT - loss of power under load -- please HELP

Thanks JB

 

[reeldutch]

Re: only 3800 RPM at WOT - loss of power under load -- please HELP

i would not atempt to remove the plugs at wot.
you are hanging over the transom to unplug the wire and the motor wil cut one cylinder what do you think wil happen?

you will be off balance with a fluwheel next to your arm or neck.

dont do it.
get a cheap timing light for 40 bucks and you will see if the cylinder cuts out.

i suspect you are cutting out before the 3800.
you stated that its not as fast planing?

it might be as stupid as a bad spark plug/wire
or a airleak at your fuel filter.

just do the tests. and you will find out.

 

[jrousell]

Re: only 3800 RPM at WOT - loss of power under load -- please HELP

Just one quick question before I make one( or make the 30 minute drive to the nearest auto store...)

If the motor is starting and running so smoothly - is it very likely that one of the cylinders is not getting spark at regular turn-over rpm that I would perform a spark test at?

From my little experience with similar in car engines I would sense a rougher running at idle wouldn't I?

just curious...

THANKS for your time!!! Really appreciate everyone's help!

 

[ezeke]

Re: only 3800 RPM at WOT - loss of power under load -- please HELP

Thanks JB

 

[jrousell]

Re: only 3800 RPM at WOT - loss of power under load -- please HELP

Captain

You menatioend I would nto feel "it"
Not feel what-- rough running? if that is what you meant- I shoudl probbaly have clarrified. teh boat is in teh water rigth now- and under load it is running very smooth.

When I am at full load in the water it is not rough at all- very smooth. Had My father and brother (both seasoned outboard owners) and they agreed it was running very smooth at both idle and full throttle ( which was only 3800 )

 

[reeldutch]

Re: only 3800 RPM at WOT - loss of power under load -- please HELP

what rpm does it idle in gear?

 

[jrousell]

Re: only 3800 RPM at WOT - loss of power under load -- please HELP

idle in gear? --- I didn't even notice- same as always it seemed to me. I can check and get you exact number.

 

[reeldutch]

Re: only 3800 RPM at WOT - loss of power under load -- please HELP

it should idle around 750/800 rpm

the sparktest you do beacause if you have a coil thats breaking down it will give you weak spark.
the spark should be nice crisp bleu.

or you might have no spark at all at higher rpm and fine at idle.
that why you need the timing light.
you just hook the timing light to a positive and negative from the battery and the signal wire to one of the spark plug wires.
it wil wrap around the wire.
so every time your plug is firing the timing light will fire/flash also.

you have to check all 4 plugs/wires this way.

that for shure will tell you if you have an ignition problem.

fuel

if you have a airleak it might not be pressant at idle (low vacuum).
at wide open throtle that fuelpump puts more vacuum on the fuelsystem that you could suck in air.
you will not notice any sneezing/coughing because of the higher rpm.
you are running lean in that scenario.
it will cause major engine problems.
when you are running lean you have not the right fuel air mixture of 14.7 to burn.
lack off power .
if you hit the primer at wot or whenever its lacking power and you pick up rpm's, that means that you where starving for fuel.

in that case there are more things to trouble shoot.
start with the simple things first.

 

[jrousell]

Re: only 3800 RPM at WOT - loss of power under load -- please HELP

MANY THANKS for takign your time to explain this in such great detail to me.

I really do appreciate your time!

I do not have a timing light. Is this what I woudl need to get( below)?
http://www.amazon.com/Actron-CP7527-Inductive-Timing-Light/dp/B000BSY9J4

 

[reeldutch]

Re: only 3800 RPM at WOT - loss of power under load -- please HELP

yep something like that.

glad to help you

hope we can fix it.

good luck

 

[iwombat]

Re: only 3800 RPM at WOT - loss of power under load -- please HELP

If you can find one . . .

Get a timing light with a built-in tachometer. A bit spendier, but a pretty handy tool to have.

 

[jrousell]

Re: only 3800 RPM at WOT - loss of power under load -- please HELP

ok- I went out and bought a timing light. At idle all four spark wires seem to work well. Sounds like I have to get a friend and try this at WOT to see if one is missing out right?


I also went out and tried running off a small auxiliary tank with new gas lines just in case there was some small ait leak on the main older lines.. it didn't make any difference... nor did giving the bulb an extra squeeze.... So it looks liek I am ruling out gas line issues.

That leaves ignition at WOT which I will check with my handy dandy new timing light, and carborator.. -- that sound right?

 

[reeldutch]

Re: only 3800 RPM at WOT - loss of power under load -- please HELP

did you push in the primer at wot?

see if it picks up when you push in the primer.

you are going to find it.
dont rule anything out yet.

 

[jrousell]

Re: only 3800 RPM at WOT - loss of power under load -- please HELP

I tried pumping the primer bulb at WOT -- no effect. tried it on main fuel setup as well as off an aux tank with new fuel lines...

( i had prevously replaced fuel filter becasue I suspected it might needed it and might be related...and the hoses inside are all in good condition and tight too.)



in response to previous poster who asked what idle rpm was ---> right about 700 or 800