Somebody educate me please

[Z-man228]

Are there any wear parts under the flywheel of a 1988 yamaha 150 that control timing advance/retard? I recently installed a new CDI and just ran compression on both my motors, motors now run fine. I warmed up both motors prior to checking compression and all cylinders were between 95-100 psi. Only reason I am asking is because I have noticed a slight drop in rpm over the last couple of years. The boat is a 1983 mako 254 (heavy boat) and I have only ever gotten 5000-5100 WOT over the 10 years I have owned it. I know the motors could be moved up a hole or two and I could change props to increase rpm but before I do anything I want to make sure there is not something else I should be checking first. Both motors give good electrical output and run very well. Just wondering if there is something else out there that could be causing a drop in the RPM's that I am not aware of.

[99yam40]

timing is easy to check if you think it is a problem

[DennisG01]

You mentioned that the RPM's have dropped. What were they before and what are they now? Did they drop immediately after the repair? Or, are you saying that they have always been lower than what you expect? If the later is the case, then from what you wrote I don't see a problem. Either raise the engine (depending on where it is now) or drop pitch. What is the MAX RPM range for your engine?

[Z-man228]

operating range is 4500-5500 rpm Always ran around 5000-5100. Now Only getting 4900 buy the guage. that's why I ma questioning if there are any parts (bushings) under the flywheel that need to be checked or could it be a simple sync and link.

How do you check timing? do you need a degree wheel or can you do it with a regular timing light

[DennisG01]

You still didn't mention when this drop started happening (see questions above). Knowing that could help in diagnosis.

What do your plugs look like? Wires?

Someone correct me if I'm wrong, but when I changed the stator on my engine, I don't remember seeing anything under there like bushings - the stator just pressed/bolted onto the crank. I'm only assuming yours is at least similar. Take a look at a parts diagram - that will tell you for sure.

[Z-man228]

I Just noticed it after I changed the CDI. I rarely run the boat WOT and If i do it is only for a short burst before loading on the trailer. Running in the Atlantic and out 30-40 miles in the gulf i rarely get good enough days to pour the coal to it. I will definetly check the exploded view (forgot about that). Then I may raise the engine a couple of holes and contact Prop Gods to see what they can come up with

[rodbolt17]

a MUCH better bet than praying to the boat and luck gods.
simply find a REAL dealership that has test wheel YB1626.
the beg bribe or steal it.

if that motor can spin YB1626 at 4900-5100, chase hull/rigging issues.
if it CANNOT chase engine issues.
yes Virginia, its that simple.

[Z-man228]

Thanks Everyone. I have always suspected I should be able to get some more out of it but rarely push the engines that hard. Would be nice to get it to be a little more efficient. I will raise the motors a notch or two and steal the props rodbolt referred to and go from there. I assume they make a counter rotator as well? Will post results when I get them

[99yam40]

You do realize that is just a test prop that you run in a tank or in water on trailer or tied off to a dock real well.
you could test one motor at a time even as the boat does not need to move

[rodbolt17]

and that test wheel can test both enginges

[99yam40]

That is interesting,
does not matter which direction it is turned?

[RayBersch]

99YAM - No one has answered so I will jump in.

Think thrust, not spinning direction. When a prop pitched to provide thrust with a clockwise spin is placed on a shaft spinning counterclockwise the thrust will be in the opposite direction, unless of course the run up is done in reverse gear which I am not sure would be wise - so, yes, that could indeed get interesting when testing for WOT rpm. Or, perhaps a test prop has some sort of neutral pitch - never used one, but would like to know if that is the case and if so, how does that provide sufficient load to test WOT rpm?

Ray

[rodbolt17]

pay no attention to the old man behind the curtain.

the test wheel gives negligible thrust, simply a KNOWN load.

and yea, TOTO got away

[99yam40]

Yea I knew no thrust,
just did not realize it would do it either way you turned it
I learned something new today so now I can eliminate some more brain cells

[RayBersch]

pay no attention to the old man behind the curtain.

the test wheel gives negligible thrust, simply a KNOWN load.

and yea, TOTO got away

Now you see, that's why I read these things (and seldom reply) because I like to learn - no thrust, known load - all makes sense. Thanks

Ray