Fresh motor rebuild, but not sure what to expect???

[NEKFORCE]

So thanks to everyone on here I finally got a chance to take the boat out with my fresh motor rebuild i just did. The thing started, idled and ran great as we cruzed around, i tried not to push it to hard until i break it in, and i am running the gas mix really rich right now just to be safe. I don't know much about boats and dont know what sort of power it should have. Its a 1989 Force 125 on a bay liner capi, I believe its 20'. I don't really understand the tilt and planing the boat at the minute, so with the motor all the way in the down position it made the nose of the boat really point up, and i really could only do what the speedo said was 10 - 15 mph. does this sound correct? I have been told by the previous owners that it will do 40mph. Was this just because I don't know how to run the tilt, or do you think something is wrong? Running and sounding wise everything seemed excellent. I did discover when i stopped and was just floating with the motor off, when I wanted to restart it I needed to tilt the motor up some, not all the way down or it would stall when first putting it into gear. I think this is normal, and normally when running off the hose , it goes into gear just fine and will not stall. It idles quite low (rather nice really), but i have my idle screw turned all the way up. I know two stroke motors, but not boats in general, and i want to make sure this all sounds like its doing what it should power and speed wise. I have attached a picture.

 

[pnwboat]

Do you have a tachometer? Knowing what your RPM's are really helps in determining performance, tuning, setting idle speed etc.

 

[NEKFORCE]

You know, I really need to pick up a cheap one. Typically i am working on cars and things that have their own tach.
did you see my photo, the thing went pretty darn good, i think i just dident do the tilt correctly.

 

[Jiggz]

Tilt and Trim are two different things when it comes to these motors.

Tilt, basically it is used to raise the motor off the water when launching or recovering to prevent grounding it on the ramp or shallow waters. Finally, if you are trailering, you want to tilt the motor all the way up to prevent hitting bumps on the road.

Trim, it is used to keep the boat at plane with the water as much as possible. It is adjusted based on the loading of the boat, its speed through the water and also sea state (height of waves of the water) It is not an exact science but here's the simple rules to follow to max out boat speed through the water.

Basic rules:

Trimmed out - means the trim piston is extended all the way out. When fully trimmed out, the reaction of the bow of the boat is to go up. Depending on sea state or waves, loading or speed, the boat tendency is to jump up and down like a porpoise or dolphin jumping out of the water, hence the term, "porpoising"

- You do not want too much porpoising as the boat loses speed by directing the forward force of the motor up into the air instead of through the water.

Trimmed in - means the trim piston is retracted all the way in. The reaction of the bow of the boat is to push down on the water. When waves are high, you want to trim in the boat to keep the bow down for a smoother ride and avoid overturning the boat.

- However, you do not want too much trimmed in for the boat will instead be "plowing" through water hence directing all the forward force of the motor in "pushing" water instead of running through it. Hence, slowing the boat speed through the water.

Important to note, at full speed, the trim cylinder can barely push out the motor to trim it out. On the otherhand, it is very easy to trim in the motor during underway. In short, you always wanted to start with all the way trimmed out and as soon as you get on a plane adjust to trim in to max out forward speed. Lastly, you cannot tilt the motor while doing speeds in excess of certain speed or anytime the boat is in a plane. The tilt cylinder is just not strong enough.

 

[ShaneB23]

Thanks for that Explanation Jiggz. It's actually super helpful

 

[Jiggz]

You are welcome. Trim adjustment as I mentioned is not exact science. It's an experience thing. It's always the big discussion between me and my daughter when she's driving the boat. At WOT she can barely get 30 mph while I can do 40 mph, on exactly the same configuration and sea state. However, she drives the boat so smooth it barely gets the bow off the water, not realizing she's plowing heavily hence slowing the boat down. But then she's still in her learning stages.

Personally, I find the sweet spot to be where the bow porpoise or get off about 1~2 times every 5~15 seconds.

 

[NEKFORCE]

Thnk you, I beleive my boat is running correctly i just dont know what to do.
I have the motor like all the way down, and the bow pointing way up, had a huge wake and could only do about 10mph top speed.
at one point i lifted some and seemed a bit faster.. like 15 I bet i was just plowing cause i had the motor all the way down.... i dont wanna race around i just want to know the boat is runnning operating correctly. Honestly 10mph was fast enough for what i want but i just want to know its right

- However, you do not want too much trimmed in for the boat will instead be "plowing" through water hence directing all the forward force of the motor in "pushing" water instead of running through it. Hence, slowing the boat speed through the water.--------this is what i think i was doing?

 

[jerryjerry05]

Look at the motor when the boat is out of the water.
​The cavitation plate.
​It should be at 90d from the back of the transom.
That's a starting position, get it going and apply more power.
​Than as you speed up, raise the trim a little at a time.

Does the motor rev up and just not go anywhere?

 

[Jiggz]

As previously mentioned you need a tach to diagnose your problem accurately. The rpm will indicate whether the motor is not able to come up to speed, or if it does then it could be a spun prop or maybe even an undesized prop (if you changed it).

 

[NEKFORCE]

It revs and runs fine, i don't think i have any problems other than I dident really understand how to run trim tilt, and have never seen this boat drive before so i didn't know what to expect. I have never even been on a boat like this before this.

 

[Jiggz]

I see. Enjoy and have a great boating season.