S150TXRU won’t rev past 4200

[JerEazy2]

Engine is new to me, as is boat. During the test run the engine didn’t go past 4200 either. But I attributed this to heavy load, a badly corroded prop (13.75x17) and a bottom that needed 3 hrs to clean the barnacles off.

Well the speed picked up after cleaning the bottom and installing a 4 blade 15x15 prop. But 4200 is still the number.

To deacribe the problem more exactly, the engine idles great at about 8-900I’m neutral, 7-800 in forward gear. Revs perfectly up through the RPM range. But the engine reaches about 4200 at 3/4ish throttle. Pushing the lever any further makes no change in tone, sound, RPMs or speed. I’ve been on boats before where pushing it down you would still hear the engine sucking air and trying to go, but just won’t. That’s not this case. While in the water, it did free rev past 4200 with the drive disengaged (carefully up to 4400 - could have gone higher but didn’t want to push it)

all filters changed, new plugs properly gapped, old plugs had some oil on them, but not bad.

my thoughts went straight to the carbs needing a rebuild and probably clogged jets. But, you guys are the experts and I wanted to float it out there for confirmation, and/or other ideas.

thanks!

[rodbolt17]

are you an idiot?
why EVER rev an engine with no load??????
now find a dealer with test wheel YB1626 and simply test it. that will tell you instantly whether you have a prop/hull issue or an engine issue.
not the first engine I have seen overpropped.
but please quit reving it with no load.
a Z200 will hit 4000 RPM with no load and only sparking 2 cylinders.
see what I am saying?

[99yam40]

I would try a different prop before anything else.
or a good Yamaha shop should have a test wheel to see if the motor is doing what it should so you could eliminate it being a motor problem if it runs at the spec RPM..
we have no idea what boat you have or the weight this motor is pushing

[robert graham]

Sounds like you're not getting power from one cylinder...like with a plugged injector/screen.....

[walleye1]

It is a carbed motor. Idle in neutral is to be700 +/- 25 rpm, in gear at idle 570 rpm. Wot is 4500 to 5500 rpm.
Carb mix screws are 1 1/4 turns out. This is out of Yamaha's tune up specs guide.

[robert graham]

Maybe a plugged carb jet....can cause loss of power, lean mixture, possible engine damage if not fixed. Have you checked/inspected each spark plug.?

[JerEazy2]

Rod: Yep - sometimes I am an Idiot. Wrong or right, it was done and things turned out alright. The rationale was to see if the engine COULD rev past that point. No point in explaining any further. But, yes. I will stop doing it.

The 150 is pushing a pursuit 2150 DC

It is a carb motor. And thank you Walleye for the specs. I set the idle based on previous experience and that is incorrect. I'll back off the screw next time i'm at the engine.

Mr. Graham: I'm thinking a plugged carb jet as well. But i think i have a spare lower pitch prop in the garage i can put on as well.

[walleye1]

Get you a plug wire pulling set of pliers, with the engine idleing in neutral pull each wire off one at a time
you should here a diff on eace cyld. If not clean them.

[JerEazy2]

I would try a different prop before anything else.
or a good Yamaha shop should have a test wheel to see if the motor is doing what it should so you could eliminate it being a motor problem if it runs at the spec RPM..
we have no idea what boat you have or the weight this motor is pushing

I did switch from the 17p that was on there to the 15p 4 blade. But i guess if i wanted to really test i should have kept with the 3 blade set up. The extra blade and diameter may have offset the pitch difference,

[JerEazy2]

Get you a plug wire pulling set of pliers, with the engine idleing in neutral pull each wire off one at a time
you should here a diff on eace cyld. If not clean them.

rgr that.

I ordered 3 carb rebuild kits - figuring worst case it's not a terrible repair just to do as preventative, but might also solve the problem.

Before i do the rebuilds, i'll pull the plug wires and see whats what.

[JerEazy2]

Maybe a plugged carb jet....can cause loss of power, lean mixture, possible engine damage if not fixed. Have you checked/inspected each spark plug.?

i inspected the plugs that i took out - but not after the last run with fresh plugs. I'll pull them as well and see if i notice anything of note.

[panasonic]

are you an idiot?
why EVER rev an engine with no load??????
now find a dealer with test wheel YB1626 and simply test it. that will tell you instantly whether you have a prop/hull issue or an engine issue.
not the first engine I have seen overpropped.
but please quit reving it with no load.
a Z200 will hit 4000 RPM with no load and only sparking 2 cylinders.
see what I am saying?

Rodbolt is there any need of calling the man a "idiot" Although he did not seem to take much offense to it is besides the point. You gave the man excellent advice not to be doing that to his engine. Could you not have done that with out calling him names?

Some others may come on here looking for advice and would take much offense to that and cause a pissing match or simply leave. I think responding in a respectable manner is part of a good forum.

Panasonic

[walleye1]

That is perty much the way harden techs take it and talk that way,, I'm one.

[JerEazy2]

Rodbolt is there any need of calling the man a "idiot" Although he did not seem to take much offense to it is besides the point. You gave the man excellent advice not to be doing that to his engine. Could you not have done that with out calling him names?

Some others may come on here looking for advice and would take much offense to that and cause a pissing match or simply leave. I think responding in a respectable manner is part of a good forum.

Panasonic

It's fine. I've been called worse. But thank you for the comment.

I'm just happy I wasn't the idiot who revved his engine that high while hooked up to muffs or the flushing attachment. At least i was in the water!

Everyone has different ways of approaching things - And knowing Rodbolt from not only lurking here, but other forums as well; I welcome a bit of a verbal beat down from him. His advice is normally spot on.

Though i will say in this case i'll be rebuilding the carbs and (attempting) a link and sync before i even think of taking it to a dealer here in Sarasota. Just one of them looking at it will cost me $500.

[ausnoelm]

How about a very simple, no cost check and see if the throttle is indeed opening fully? will take about 5 mins to do, without engine running of course!