I've posted this on 2 other forums, so please excuse if you see this again.. just trying to get some quick help.

2008 Optimax Pro XS 225 with 480hrs.

I just got a prop out of the shop and took the boat to test it out today. Started right up like usual, ran it for a few hours most of the time at WOT since speed is what this prop is supposed to accomplish. Not a hiccup, turned full RPM, ran perfect.

Anyway, go to power load on the trailer. Hammer down, and motor bogs down and wont go over about 1500rpm. Literally doesnt have the power to push the boat on the trailer. So I take it back off the trailer.... Go to run it again, and sure enough, jumps right out of the hole and once again runs wide open no problem. Go to get back on the trailer, same problem. Wont go over 1500rpm. Take back off trailer, run it even longer, screams like a new motor, then same thing happens when trying to power on the trailer. Weirdest thing I've ever seen!

Only thing I've done diagnostic wise (and I BELEIVE this might be the issue, but want to double check): I put my coil tester on and tested all 6 coils.. The #5 coil doesnt light up as bright as all the others, so I assume this may be my issue. However, the reason I ask is because I've already replaced 2 coils, but when those went bad, they didnt light up at all and the boat wouldn't even get on plane. #5 coil still lights up, but is much dimmer than the others.

Fuel filter is only a few weeks old.

Taking the boat out of town this Thursday which is why I'm trying to get some quick input before I buy a coil.

Any other ideas throw em at me. Thanks everyone

Are you trimmed up when you power load? Running at wide open throttle is trimmed down so assume you're trimmed up quite a ways when loading? Maybe has something to do with that? Fuel line kink trimmed up?

Yes sir trimmed up.. That's why the prop was in the shop in the first place, a boat ramp got it.. lol. I didnt think of that, could be possibly. But at the same time, when I'm on plane running WOT I'm trimmed up the same amount as I am loading up.

Well, then that ain't it. That's pretty crazy man.

You're telling me!

Like I said, one of the coils isnt lighting up as bright as the rest, so that's my assumption. But again, I'm getting assurance because the past two I replaced didnt light up at all and the boat wouldn't even plane

Did you change the number of pvs plugs? Might be getting too much bite now.

I didnt change anything on the prop. Literally just got it repaired (rounded the tips of the blades off.) Been running my back up prop for a while (3 blade 25p Fury.) Prop that got repaired and is the main prop is a Turbo OT4 23p 4 blade. It ran fine on this boat to begin with, but I was also thinking that maybe the prop is biting too much?? That doesnt make sense though considering like I said, it runs perfectly fine on the water

I'm going to take the back up 3 blade to the ramp tomorrow to see what happens. I've seen crazier things....

But does anyone think my current diagnosis on that coil may sound right?

But on the water the boat has some give, when on the trailer, it has no give and the motor wants to stall out. Now I don’t know why it would be different than before, that part is odd.


I have no clue on the coil, I don’t think it would run properly if that were the case; but I’m not a mechanic. Best place to ask would be on BBC, Merc boards. Some smart merc fellas there.

Thanks for yalls help!"

How much fuel is in boat? Any chance that when the boat is going up the incline of the ramp it is sucking air. I have seen that before. All the fuel would run to back of tank and the pickup tube was slightly ahead of center.

Alright well figured out the problem

Anyone who said it's a propping issue, beers for you.

Went down to my local ramp... backed it in with the 4 blade (the one I had fixed) and it was doing the same thing I mentioned. Wouldn't go over 1700rpm on the trailer.

Pulled out, threw my old 3 blade on, and I'll be god danged if it screamed like a new motor.

I repeated this process 6 times just to make sure it was the issue. Sure enough, everything runs perfectly fine with my 3 blade.

So now that we know this, heres the only I can think of.. is it possible that the prop is slipping on the shaft? My guess is when the motor feels that it's not under a load and not pushing, it wont rev over 1500rpm.. so the only thing I could guess is that the inside of the 4 blade is worn out and not getting a grip on the shaft

Like Grout-Stout Stated. Vent plugs. I run a 25 Fury on my Triton and have all holes plugged. Just to get it to load.

If the prop was slipping in the hub rpms would be very high, not low. Different props act very differently, higher speed props usually have less power for loading although I am a bit surprised you still have a good holeshot with it. Also it is a 24p compared to the 23p so it has less power there also. I have had a few setups that ran great on the water but did not power load well, usually had to back the trailer further down the ramp to load them...

You might have a coil issue as well. My 08 250 had a factory recall on the coils. Sounds like that’s not the culprit but may be something to take care of anyways.

Raise your jackplate up and get the motor out of the water. Mine did the same thing once and that fixed it.

If your motor is running good as you have stated then it’s fine.

Mine used to do it on steep ramps and the lower cowling was under the water