Post Break in Performance

[Whitedog]

A question on Performance during and post break in. I am presently breaking in a new Yamaha 3cyl 90 hp 2 stroke. I am running 50:1 premix along with whatever the oil injector provides. My question is: can I expect any difference in performance when I go to straight gas along with oil injection. Specifically will there be any change in RPMs?

 

[Perfidiajoe]

Re: Post Break in Performance

When I broke in my Merc, I noticed very little difference, & I did my 20 hour service(required) at the same time I stopped mixing gas & oil, including replacing the plugs. So I say not much, but it ran great then, & still does. It sounds to me as if you are not happy w/ your performance, if that is true, let your dealer know. Good Luck, Joe

 

[Perfidiajoe]

Re: Post Break in Performance

One more thought Whitedog. Did dealer install the engine, maybe the prop is wrong for your boat? The right prop can make a world of difference, especially in the R.P.M. department. Again, Good Luck, Joe

 

[Whitedog]

Re: Post Break in Performance

Joe,<br /> Yesterday was the first outing on the boat. The tach was setup wrong. It read 2200 on idle and 7000+ @ WOT. I removed the tach and set it to the correct setting. Yesterday it sounded like the motor wasn't making the right rpms and hole shot was lacking. Today the tach read 4500 @ WOT with 38 mph by speedo. So I am assuming my ear was right. The prop is a 13.25X17 stiletto with cup. This is the prop recommended for this boat. I checked the throttle linkage and it fully opens the butterflies @ WOT setting. My dealer told me if I wasn't satisfied with my rpm range he would exchange the prop as long as I didn't plow up any oyster reefs. I'm thinking about requesting a 13.25X15 cupped prop. Any suggestions?

 

[Solittle]

Re: Post Break in Performance

What is the max RPM at WOT called for in your owners manual? Most OMCs call for 5500 rpms.<br /><br />What boat do you have this on? Where is the cavitation plate relative to the bottom of the hull? The pitch of the prop is only part of the performance equation.

 

[Paul Moir]

Re: Post Break in Performance

Just to fill in some details on this post, the gear ratio is 1:2, and the WOT range is 4500-5500. Running the numbers, the 4800RPM seems accurate so long as that speedo is close (38.6 w/ 0 slip).

 

[Whitedog]

Re: Post Break in Performance

The hull is a Nautic Star 1800 Bay. Hull weight is 1200+/-. Cavitation plate is approx 1" above absolute bottom of the V. Last boat I had was a 16 ft Hydro Sport Center console. Boat was 300# heavier and had a more pronounced V. Motor was a <br />Johnson 90 hp with a 13x17 prop. This combination would top out @ 42 mph before the rev limiter would kick in and shut me down @ 5750 rpm. My dealer tells me I should be pushing 5500 or higher with this motor. Rev limiter is about 61-6200 rpm (dealer tells me).

 

[Dhadley]

Re: Post Break in Performance

The 17 sounds about right for that boat. If youre that far off on rpm and its a new motor, why not let the dealer deal with it? It should be under warranty. And dont let him just throw props at it. Youre looking for 1000 rpm. Thats more that a prop change.

 

[Perfidiajoe]

Re: Post Break in Performance

Is this a 3 cylinder yam. 90 Hp? Look in your owners manual, it should give you a wot Rpm range. Generally 1" of pitch is worth about 200 Rpm's, if this is new, as i believe you said it was in the first post, go back to the dealer, don't try to tell him what's wrong, just that something is wrong. Let him handle it you already paid him for that. Ask him what he thinks, & why, everybody will be happier your boat will run as it should, & he won't have to guess at what's been done. Not to say that you don't know, or can't fix it, but that's why you bought NEW. IMHO, Joe

 

[Whitedog]

Re: Post Break in Performance

Swapped Prop today for a Stiletto 13.25X15. Little motor woke up, lake was rough so I did't push the issue to much. I gained about 600 rpm and 2-3 mph bouncing through the chop. As soon as the wind either settles down or switches to a more favorable direction I'll get a better idea what the new prop will really do. As for my dealer, he has been great. He brought the prop 30 miles from his shop to me, he also said whatever it takes to get it right he'll do. He even said he'd upgrade the boat to a 115 hp if we can't get the 90 dialed in right.

 

[XcellR8]

Re: Post Break in Performance

Originally posted by SoLittle:<br /> Where is the cavitation plate relative to the bottom of the hull?

What effect does this have? I'm having a similiar problem with a 91' 90 hp Merc that appears to be over propped (on a 15'6" FG boat). My cavitation plate is even with the bottom of my stepped V hull (mounting holes are the second one down from the top).

 

[XcellR8]

Re: Post Break in Performance

Originally posted by Whitedog:<br /> Swapped Prop today for a Stiletto 13.25X15. Little motor woke up, lake was rough so I did't push the issue to much. I gained about 600 rpm and 2-3 mph bouncing through the chop. As soon as the wind either settles down or switches to a more favorable direction I'll get a better idea what the new prop will really do. As for my dealer, he has been great. He brought the prop 30 miles from his shop to me, he also said whatever it takes to get it right he'll do. He even said he'd upgrade the boat to a 115 hp if we can't get the 90 dialed in right.

FWIW I'm having a similiar problem with a 91' 90 hp Merc on a 15'6" FG boat. It came with a 13-3/4" x 21 Trophy Plus SS 4-blade prop. 4400 rpm at WOT with a top speed of 39 mph (on it's speedo). I noticed with this prop the rpms don't seem to climb as quick as they should and the motor appears to lug along when in gear with barely any throttle applied. <br /><br />I borrowed a 13-1/2" x 19 std 3-blade aluminum and with that it runs at 5200 rpm at WOT with an increase in top speed of 2-3 mph. I found the boat is able to build rpms much quicker and as a result planes easier so it appears it's a step in the right direction. I also noticed the torque steer is a lot less with the aluminum 3-blade.