Power and RPM falls off in full throttle

[saltlife50]

Hello all, this is my first time writing in the forms but I have been reading for a while now. First some background my motor is an outboard 1992 OMC v115slend from what I understand it?s the same as the Johnson/Evenrude of that year. The problem I am having is that when I am running at full throttle the motor runs great for 3 or 4 minutes, and then it just starts loosing speed and rpm. It will slowly go all the way down to just above an idle speed. If you pull the throttle back to neutral and leave it there for about 30 seconds it works fine for maybe a min and then the same thing all over again. I have rebuilt the carbs, new fuel lines, fuel filter, running on a new fuel tank. My compression check are all within 4psi and I did a spark check that also seems fine. I think the previous owner upgraded the VRO pump because it has the removable attach points or the fuel line and the pulsar has a blue ring around it. Could this be the fuel pump?
Thanks in advance for the help.

 

[jonesg]

Re: Power and RPM falls off in full throttle

Never enough info eh?

Engine history, new to you?
Has it ever run good?
Does it run rough when it cuts back?
Does the alarm system beep when you key the ignition on?
What alarms are you getting when it cuts back by itself.
The alarms tell us what is happening.
Are you running on pre-mix or VRO oil tank?
Running 3-4 minutes then bogging down sounds like the carb bowls are going empty, have you tried pumping the bulb to keep the bowls fed?
Does the bulb go flat?
Is the arrow on the bulb pointing AT the engine?
needs more info !

 

[saltlife50]

Re: Power and RPM falls off in full throttle

No I bought the boat from a guy that had it sitting up for a year and it did not run at all when I got it. After I cleaned the crab and replaced the fuel components it started running. It?s been running ok but the engine dyeing down is new (last 2 times out). It doesn?t run rough when it dies down it?s like I throttle down. Sometimes the alarm will sound a steady tone when I turn the key. No alarm when it cuts back. Still running the VRO and I have been monitoring the oil tank and the oil level is going down. I have not tried to pump the bulb while moving. The bulb does not go completely flat but it does not stay hard either. Normal? The arrows on the bulb are pointing at the engine. Also the Tac stopped working and I don?t think my battery is charging. I had a hard time starting it yesterday after I was fishing. Haven?t had times yet to check the Tac.

 

[jonesg]

Re: Power and RPM falls off in full throttle

Bulb going soft is normal.
Order the factory service book.
I wouldn't take it out until its fixed properly, its so easy to melt a piston if something is faulty.
The alarm system has to be fixed, its your lifeline.
Does it beep once when ignition is keyed on, yes or no
It sometimes beeps constantly when turned on ok, but do you get the test beep the rest of the time?

You need,
compression guage.
Adjustable spark tester (NOT neon type)
simple multimeter.

Do a compression test and a spark test with a 7/16th inch gap on tester.
Take a volt reading at battery, and again with engine running.
Write down results and post back.

Get service manual below, best money you can spend on boats.
Don't waste money on seloc or clymer service manuals.
www.outboardbooks.com

 

[saltlife50]

Re: Power and RPM falls off in full throttle

Ok so I finally got time to check.
Spark is good, bright blue now. At first number 3 had no spark butt after cleaning the groung it works.
Compression is 110 to 115 on all 4.
Battery is at 12.73 motor off butt now when I try to start the motor the starter just spins and dosent engage the flywheel. Any ideas.

 

[mikesea]

Re: Power and RPM falls off in full throttle

Your problem could have been the dropping of that coil,but Im thinking 2 problems.the throttle down is sounding like a fuel restriction somewhere.Sounds like you get up OK ,but then the bowls start to empty and dont fill fast enough ,or ,the floats may not be right.You say new tank,is it venting properly,if its possible its not venting,simply open the fill cap and see if it corrects.Definatly try the squeeze the ball trick ,you basically over ride the fuel pump,if it picks up,it very well could be the pump.As for the battery,you could still have voltage ,but no amperage.Will the engine crank on a known to be good battery ,or with a boost.If so you could have a bad battery,but ,once running ,test at the battery posts with the idle up a bitnote what your getting for voltage,it should be about 14 ,if not,you may have a blown rectifyier.To save my fingers ,search the forum for one of the many easy tests.Its the triangular part with 2 yellow and a red wire.

 

[saltlife50]

Re: Power and RPM falls off in full throttle

Ok so I did some more research on the forums and found a good trouble shooting tree for my problem and what do you know it works. Cleaned all the grounds and battery cables and it worked the first time. I think it is still missing when it runs I still need to test the rectifier. It seems to be intermittent can the rectifier do that or is it a go no go part? Still not ruling out the fuel pump I?m taking the boat out tomorrow and will check the pump and post back. O and I do get a beep from the alarm on engine start.

 

[saltlife50]

Re: Power and RPM falls off in full throttle

I was poking around on the motor testing resistant?s on the stator 1.3 ohms and found 2 potential problems. 1. The priming bulb would not get all the way hard so I swapped it out with another one and now it gets hard as a rock. 2. Now that the primer works and is putting pressure on the fuel pump I found a small fuel leak coming from a split in the screw hole where the fuel supply hooks up to the bottom of the pump. It is very slow one drip every few pumps. And I removed the pump and looked inside and there is no damage. So does anyone think that this could be enough to cause my problem?

 

[saltlife50]

Re: Power and RPM falls off in full throttle

Engine running I have 12.73 volts at the battery. Tested the red wire coming from the rectifier and it was 12.73 under several RPM ranges. And trying to touch the gray wire from the tac to either of the yellow wires results nothing. Blown rectifier?

 

[emdsapmgr]

Re: Power and RPM falls off in full throttle

Any leak in the fuel system can cause problems. If fuel leaks out when priming the hose bulb, air will leak in when the engine is running-reducing the fuel supply. Good you got the leak fixed. Charging issues (battery voltage and the rectifier) are separate issues from the ignition side of the engine. Typically the rectifier/regulator does two things, recharge the battery as well as a provide a signal to run the tach on the dash. Usually when the tach starts to act up, a discharged battery may be next.

 

[saltlife50]

Re: Power and RPM falls off in full throttle

Tach is defiantly not working but I was holding my multimeter to the battery today and it did charge but only to 12.73. On a side note when I was running today on the muffs I noticed the pee stream was pretty week. Is it possible that my problem the entire time was the engine was getting to hot and retarding down?