Yamaha engine question

[Halfhitch]

A few months back I bit the bullet and repowered with a new 4.2 liter F225XB. I would have liked to have the electronic model but it would have been another thousand bucks. Anyhow the old F225 had a 2:1 ratio in the lower unit and the new engine has a 1.75:1 ratio. That 12.5 percent of increase in shaft speed made the 15 1/4 X 19 prop off the old 225 too rich for the new engine. I'm too old to be a speed demon anymore but I want stuff right so the last time out fishing and as we got back inside the ICW, I opened her up for a bit and ran about a mile with the hammer down. The rpms ran right up to 4800 and sat there the whole time. Right off I got to thinking that I needed a different prop and that belief is still with me but before I start trying out a different prop, I want to make sure the engine is actually going full throttle. I noticed after the engine change that there was more travel on the binnacle lever after gear engagement before the rpms started to pick up than there had been on the old engine. That got me to thinking that I should check the cable adjustment at the throttle lever. When I checked it out, it was obvious it was a different animal than I am accustomed to. I am hoping some of you guys have some knowledge about this that you could share. The question I have is...should the full throttle position be when the little hash mark is lined up with the arrow or should full throttle be when the stop on the lever contacts the stop?

This is at idle position...

This is where the throttle stops at this time and where it was when 4800 RPMs was the best it would do...

This is at the full stop when I unhook the throttle cable and push it till it actually hits the stop like the old ones. Is this where the binnacle lever should be taking the mechanism to get full throttle?

 

[Gianni]

I dont have an answer to your question but seeing the boat you have and that size motor, she must boogie!!

 

[Halfhitch]

Yes, it gets right with the program but only turning 4800 WOT tells me something is not right. I was just hoping someone here knows about this style throttle mechanism.

 

[DennisG01]

I don't know that engine, but the part where you said "there was more travel on the binnacle lever after gear engagement before the rpms started to pick up than there had been on the old engine." leads me to believe that you are saying that you shift into FWD idle, then as you advance the throttle you don't get any RPM increase when you would normally expect to... taking more throttle movement before the RPM's start to increase. "Logically" thinking, I believe you answered your own question. Adjust the cable, but make note of where you start in case you need to put it back the way you found it. I don't see any way that you're going to hurt anything by trying.

Maybe pick-up a service manual?

 

[SkunkBoat]

Not familiar with the model but if you are only turning it to ten, you aren't turning it to eleven
Eleven!

 

[Halfhitch]

I have a service manual but under the rigging section it only explains how to install the end of the cable housing in the clip and how to unscrew the clevice until it will slide onto the throttle pin. As you can see, item #9 simply states "check the throttle cable for proper operation" with no mention of determining a full throttle position of the mechanism. I was hoping to be able to determine this without having to remove the air box assembly. I was hoping someone might have this model engine and would be willing to have a look at theirs when their binnacle lever is at full throttle to see if it only rotates that mechanism part way. Just seems strange. I have no confidence in the job the rigger did because he botched the trim tilt indicator calibration completely and when I called to talk to him the salesman that I had just handed an $18000 check to wouldn't let me talk to the mechanic about it. I won't be contacting them again.

 

[DennisG01]

It looks like you do all of the adjustment at the idle position and then the WOT takes care of itself. Try doing/double checking what it mentions in #6 & #7.

 

[Legend]

Not an answer to your throttle question but a thought. I had F225's with 15 1/4 x 19 props. When I went to 4.2L f250's I had to change the props to 15 1/2 x 17 to get 5,800 RPMs. With the old props on the new engines I was only getting 4800 RPMs.

 

[Halfhitch]

That's good to hear Legend, That's the same RPMs I'm seeing with the 19s. So maybe this thing is cranking out what it is supposed to. I will move on and drop a couple inches of pitch and maybe drop an inch in diameter. I can get a really good deal on a Power Tech 14 1/4 X 18 no cup. Do you think that would be enough difference to get my RPMs up?

 

[Legend]

Worth a shot, any way you could borrow one before buying to see if it works?

 

[wrxhoon]

18" won't be enough, you have to go to 17" pitch . In your old 3.3 with 2.0 box at 5800 RPM and 19" you have 2900 prop revolutions . With the new 1.75 box at 5800 and 17" you have 3314 prop revs. Very similar speed with both so that would work about right the new engine will give you about 1 mph extra speed.

 

[Halfhitch]

I think you are right. I also just found this by Grady White. This is my boat model. I was surprised at the prop diameter.

 

[SmokyMtnGrady]

Wow, if that's the case, you're a good bit out of specs on the prop. Call Ken at Prop Gods and he will do you a solid and get you hooked up with the right prop. I recall reading some where for every half inch you drop in size your RPMS go up 500? Maybe it's an inch? Either way ,you are looking at least 1,000 RPM by dropping down in size.

 

[Ky Grady]

I'll have to agree with Smokey on contacting Ken at Prop Gods. At a minimum you should have been spinning a 17P prop. What hole is your motor mounted in? Have seen cases where couldn't get good RPM's because motor mounted to low. I hope that's a typo on hub diameter on the Grady report, that small of hub you'll be getting exhaust flow around outside of the hub affecting your bite in the water, i.e.; turbulence in front of the blades affecting the grip, if you will, of the blades in the water for forward thrust.

 

[SmokyMtnGrady]

I thought the same thing KY when I read the Grady performance report. I was like that's a small prop. It could be mounted too low too. We discovered my repower was mounted too low. We being KY Grady when he was looking at my boat. My 4.2 won't turn north of 5,500. I am moving the motor up 1 hole. I would call Grady and then call Ken.

 

[Ky Grady]

The gearcase housing is the same diameter on the 3.3 and the 4.2. 15 1/4 is usually the standard diameter and a 15 1/4 x 17 is usually the go to prop for the F225 and F250. I'm spinning a 15 1/4 x 16 4 blade on my 3.3 F225, removed a 15 1/4 x 17 Yamaha prop. 13 3/4 diameter is to small for the gearcase for either 3.3 or 4.2.

 

[SmokyMtnGrady]

The gearcase housing is the same diameter on the 3.3 and the 4.2. 15 1/4 is usually the standard diameter and a 15 1/4 x 17 is usually the go to prop for the F225 and F250. I'm spinning a 15 1/4 x 16 4 blade on my 3.3 F225, removed a 15 1/4 x 17 Yamaha prop. 13 3/4 diameter is to small for the gearcase for either 3.3 or 4.2.

Typo then?
I am thinking dropping down to 15 1/4 x 16 4 blade or 17 3 blade would help get those RPMS north of 4,800. I am also inclined to speculate the motor is mounted too low. It's the internet, that's what it was built for , speculation and boat porn.

 

[Halfhitch]

The guys that rigged this engine used the Grady recommendation of hole #2 mounting position. You can see on the bulletin above, three lines down from HP is mounting hole position they used for the test.

 

[Ky Grady]

Correct hole then. I'd be looking at prop pitch.