F225 loss of 500 RPM/13 MPH

[Cape Cod transplant]

I'm stumped. I have a 2004 F225 on a 22' Key west center console. WOT was 50 mph @ 6,000 RPM. When I moved the boat from Cape Cod to Lake Michigan, I lost my top end. Last year started with the need for a new fuel pump, so I had all of the internal and external filters changed, new pump etc. Boat ran great, but I couldn't get the same top end.

This past winter I brought the boat to a Yamaha dealer and explained the problem. They went over the whole fuel system and found the compression was not ideal (not real bad but not ideal) and differed from the two banks. Everything else fuel pressure etc. was fine. Likely cause was carbon build up, so they de-carbonized the engine and the compression was great. I thought the problem was solved. The max RPM is still 5,500 and I cant get past 37MPH.

The bottom is clean, I've made no change in props, engine runs smooth and strong with no other issues. I mentioned the move from Cape Cod to Lake Michigan only because salt water is more buoyant than fresh, but that should have no impact while on a plane.

Any ideas? Could the throttle cable have stretched and just needs to be adjusted?

[TownsendsFJR1300]

IMHO, I'd pull off the cowl, (engine off) and put the throttle to full on. Then check the throttle bodies/linkages to make sure the butterflys are opening fully.

When you said you lost the top end, was that in reference to running RPM's dropping?

[Cape Cod transplant]

Thanks....Yes I meant RPM's when I wrote top end. I'll check that.

[Cape Cod transplant]

dumb newbie follow up question....where are the butterflies? It's not a carbureted engine.

[ohsoslow]

Umm, I think you should stop looking at the engine as the problem, theres no way losing 500rpm should lose you 13mph!! That just doesn't make sense at all. I'd be looking at something like a whole lot of extra weight onboard, ( I say that because I had a mate who was complaining of loss of performance, and it turned out his boat was full of water under the floor!) something wrong with hull, change of motor height, trim tabs etc etc. Which would then account for the loss of speed, and loss of rpm due to motor struggling!

my 2c

P.s. You should still have butterflies at the front of your motor just the same as a carb.

[TownsendsFJR1300]

+1 on the above, 500 RPM and the loss of 13 MPH is a bunch of speed for a small amout of RPM drop.

The butterflys are in the throttle body and function the same (also look the same) as carb butterfly's.

The only difference is the throttle body doesn't mix fuel and air together to the engine.

The throttle body butterfly allows air in (same as a carb) BUT DOES NOT ADD FUEL, the fuel injectors do that (thru a fuel rail very near the head farther down the line). There's a "throttle position sensor" atop the butterfly shaft (along with some others) that tells the computer how far open the butterfly is and how much fuel to add thru the injectors. Much more efficent when working properly, much more complicated involving electronics, sensors, injectors mulitple fuel pumps, etc...

[Cape Cod transplant]

OK, the butterfly's are short of opening fully. Do I adjust at the engine or binnacle (Yamaha 704)?

[TownsendsFJR1300]

You disconnect the throttle cable from the engine itself and cycle it forward and back a couple of times at the binnacle. It SHOULD now line up on the pin. If it doesn't loosen the lock nut and turn the plastic end in or or out to adjust, re-lock the nut. There are a set of marks on the engine assembly slide, all those marks should line up (there should be a neutral safety switch right next to these marks)..

The linkage set up on the engine does allow for the throttle to be fully open with a elongated slot on one of the linkages. As long as WOT falls within those marks, that's ok.

There is a set way/procedure to adjust the engine throttle linkage, having a manual and following it to the letter would be Very helpful....

[Cape Cod transplant]

Scott,

Thanks a million, now I know what my Saturday project is

[rodbolt17]

there is no nuetral safty switch on the F225.
there is a procedure to properly set up the throttle cable.
whats the altitude difference between where you were and where you are now?
may need a prop change.

[Cape Cod transplant]

Rod,

it looks like the butterfly could move between 1/4 and 1/2 inch (I'm not near the boat so I'm guestimating). The prop is the same one that used to push me @ 50 mph, so I don't think that's it

[99yam40]

He asked what the altitude difference was between where you are running it now and before.

At higher altitude the motor makes less HP and cannot use the same prop

Do not play with throttle adjustment if you do not have the proper procedure