150 hp Four Stroke Loss of Power

[Jerry Schaefer]

I have a 150 hp Four stroke outboard which would not go over 3200 rpm at full throttle. I had the injectors cleaned, drained the old gas, and put in new 93 octane gas with Sta-Bil and Yamaha Ring Free added. Initially, the boat hopped right up on plane and the engine would run at 5000 rpm at full throttle. However, after approximately 1/2 hr of operation at high speed (35 mph) the engine had lost power so that 3500 rpm full throttle was all it had and it was difficult to get the boat up on plane. Additionally, the engine had a rolling idle (motorboating). Any Ideas ?

[99yam40]

need to check to make sure all cylinders are sealing properly (leak down test) and are getting proper spark.

Then check rail pressure

If all is good the you may have injector problem

[Nautical]

After cleaning the injectors did you clean the filters, VST, all the way back to the tank .You may have fuel restriction if a piece of dirt got through and clogged an injector after the injector cleaning.Sounds like a restriction but like the man above says..check the fuel pressure under load when the symptoms occur.

[TownsendsFJR1300]

Drain the VST and catch what comes out. It may give you some clues. If crap comes out, use the primer and pump until you get clean fuel.

Sometimes, simply blowing back into that drain (by mouth, making bubbles) loosens up crap on the bottom too..

Rod has posted you can stick a carb cleaner hose into that drain hose(open) and the carb cleaner will clean that filter as well.

[Gregg @ PCB]

I have twin 2002 LF115's well maintained never had any problems at all 1275 hours and I am having the same problem. This is what I have done since April 2015

Discard old gas cleaned tank replaced all separators and filters multiple times
Inspected cleaned both VST tanks
replaced all injectors on both engines
replaced all fuel lines
Tune ups replaced both thermostats
Yamaha computer diagnostics 3 times shows nothing
Good compression
All work done by Yamaha Master Mechanic does not know what else to do!

Leave the dock runs perfectly 5000 rpms for 15-30 minutes then without touching the throttle will bog down to 3000-3400 rpms run at low speeds and rpms for 15-30 minutes then pick back up and run perfectly as if nothing was ever wrong. If you rev the engines up in neutral they will reach 5500 rpms no problem.

Let me know if you resolve your problem!

[rodbolt17]

two ways to test/troubleshoot it.

stand 15 ft away and throw wads o cash at it.
OR
get up close and actually test things.

what is the rail pressure at the failure RPM and load?
what is the ign coil primary voltage on all 4 at the failure RPM and load?
what is the TPS and intake pressure readings at the failure RPM and load?
see how easy this is?

and if your normal wot is 5000 RPM replace the prop as your 1000 turns off to start with.

[Gregg @ PCB]

Twin 2002 LF115's

rodbolt17 thanks for the information. I will get started on your recommendations. 5000 RPMS was just what I was running most of the time on trips boat will reach 5900-6000.

Thanks again

[rodbolt17]

59-6 Ill buy.
the rest is suck,squeeze bang and blow.

if it were a mechanical failure it would not come and go.
typically its fuel.

remember YDS can show in range failures they don't throw codes the tech has to know what it means.
Baro and intake air are prime examples.

[99yam40]

Greg, it is not cool taking over someone's threadabout a different motor.
you need to start your own.
This one if for a F150