1989 Yamaha 150 v6 rpms

[MadMax88]

Hey Guys,

Last season i had an issue with the motor not being able to turn over 3200 rpms....it would bog down etc...turned out to be a clogged carb...the motor runs very well now both at idle and full throttle the only problem is that it max's out at 4200 rpms. She runs great and is up on plane doing about 30mph at 4200 rpms, never bogs down, sputters or anything...i had noticed that there is a cam and a cam follower on this engine. the follower is worn out and when the boat is in neutral, the follower does not even touch the cam. infact, it sits about 1/8" away from the cam. Is it possible that this could be causing the motor not to turn 5500rpms at full throttle. SOmeone else had mentioned compression problems to me but i thought i would have noticed teh motor running funny (could very well be wrong though)

 

[99yam40]

Re: 1989 Yamaha 150 v6 rpms

You need to know what condition the motor is in any time you are chasing a unknown problem. Check compression and spark on all cylinders, it is easy to do and if all is good then look for the fuel problems.

Did this boat&motor ever run to normal WOT RPMs, if so when did it do that last? If you have run it with lean fuel conditions for any time at all you could have very easily hurt the pistons and cylinders

 

[MadMax88]

Re: 1989 Yamaha 150 v6 rpms

when i got the boat it was running at 4300-4400 rpms over the course of the year it had dropped down to 4200 rpms...when i took it in to have the carbs cleaned i told the shop about the boat not turning 5500 even before the carb issue...they fixed the carb issue and took the boat for a run with me...the mechanic said that the motor sounded like it was running at full and thought that my tack was off or possible a new prop might help it...tried the new prop (diff pitch) and had the same results...he said the motor was in great shape...i

 

[MadMax88]

Re: 1989 Yamaha 150 v6 rpms

the boat is a 19ft sea pro and with the 150 it is only pushing about 33-34mph with two guys in it...this is at 4200 rpms...i would think the top speed of this boat should be somewhere in the 40's which makes me think that the tack is on

 

[99yam40]

Re: 1989 Yamaha 150 v6 rpms

Rodbolt usually says to have a test prop put on and have the motor checked to see if it is putting out like it should. If it can not turn the proper RPMs with the test prop then fix work on the motor, if it can then look at the props and boat set up.

 

[rodbolt]

Re: 1989 Yamaha 150 v6 rpms

my 21 seapro with a second station and an F150 will turn 5700 at 42 MPH.
your engine is either sick or over propped.
use test wheel YB1626,back it down the ramp and see if it will turn it 4600-4800.
if it will chase hull problems, if it wont fix the engine.
any decent yamaha dealer will have that test wheel.
they may or may not loan it but they should have it.

 

[MadMax88]

Re: 1989 Yamaha 150 v6 rpms

Thanks alot guys,

When i had the engine looked at for the carb problem and had mentioned it not turning 5500, he took me out and ran it with me and said it that he felt that the engine was fine and sounding like it was turning full. he thought it might have been a prop issue as well...the prop i have on the boat is a 17 pitch and i was given another prop that was a 21 pitch...when i put the 21 pitch on i saw no difference...recently i was told that if the motor is turning low rpms that i should decrease in prop size and maybe go own to a 14 pitch which would increase rpms and speed...( i could be wrong) but it makes sense especially with yousaying it could be overpropped

 

[rodbolt]

Re: 1989 Yamaha 150 v6 rpms

if all you wish is RPMs then remove the prop, toss the prop in the creek, watch the RPMs for over speed.
if you wish to fix your issue you MUST run it on the test wheel with a known good tach,preferably an inductive model and see if the engine is capeable of spinning YB1626 at 4600-4800 RPM
if it can fix the hull or prop issue, if it cannot fix the engine.
its actually that simple.
my F150 on my 21 seapro is swinging a 13 1/4x18 pitch wheel.
yours should be close or slightly larger.

 

[MadMax88]

Re: 1989 Yamaha 150 v6 rpms

Ok Thank You

 

[rodbolt]

Re: 1989 Yamaha 150 v6 rpms

remember,my seapro is a 4 stroke not a two stroke, that and it has a hard top and second station steering and controls on the top.
lots of wind drag on mine.
either your tach is bad or your engine is sick or you have some serious hull issues.

 

[MadMax88]

Re: 1989 Yamaha 150 v6 rpms

what do you mean when talking about serious hull issues?

 

[erniefish]

Re: 1989 Yamaha 150 v6 rpms

probably the most common hull issue is a "hook" a hook forces the bow down and increases the wet area of the hull, therefore reducing speed , to check for a "hook" place a straight edge on the bottom of the boat, i doubt a "hook would reduce rpms that dramatically , but possible, good luck

 

[99yam40]

Re: 1989 Yamaha 150 v6 rpms

If you keep in in the water there could be a lot of growth on the hull.
It sounds like you have run the motor a long time with some type of problem, not hitting proper RPM, so I would start with basics and check compression and spark, use the test wheel and see where that leads you.

 

[omar3251]

Re: 1989 Yamaha 150 v6 rpms

I know this is an old thread, again..but how this issue ended, please don't forget to finished those threads, that way they could be more meaningfully.
Thanks