250 ProXS won't go over 5200 RPM, where to start looking?

[jerzia]

250 ProXS 2B360847 Much of my running time is done on inland lakes and bays with speed limits of 25-45mph depending on which body of water, so I do not get a chance to run WOT. I finally go the chance to really push it, and motor will not get over 5200 RPM WOT. Livewells were empty, and had approximately 20 gallons of fuel onboard .Motor has 286hrs, plugs and fuel filter about 20 hrs, ethanol free 87 octane with fuel cocktail and 150:1 premium plus. Prop is a 25p Tempest plus. Tackle load is average, and once replacing batteries with lithium, moved all heavy weight to the rear compartments.(roughly50lbs difference with lead wet cell batteries) The motor runs perfectly otherwise, idle is smooth, hole shot is great, mid acceleration is fine, no vibration or any other tell tale apparent issues. I realize there are several places to look for the cause, but wondering what order to proceed. I do have Merc glycerine gauges for air/fuel. I can take tests so far before getting it to a dealer, but a little guidance would be a huge help.

[JOE54]

boat make model ???? prop to pad inches ??? all linkages checked and verified ???? probably not fuel or air psi problem running smooth and great hole shot

[jerzia]

boat make model ???? prop to pad inches ??? all linkages checked and verified ???? probably not fuel or air psi problem running smooth and great hole shot

2017 Charger 210- I have hydraulic plate so p to p varies, but I will go out and measure where I normally run it. Do you mean Hotfoot and butterfly position?

Update: Unfortunately the way my boat sits on the trailer, it’s almost impossible to get a good prop to pad measurement. When I level the pad and put the jackplate where I normally run, the skeg would hit the ground when leveling the cavitation plate.

[JOE54]

yes any and all components that could affect performance , jack the back of boat up and put it on blocks or jack stands just enough to level pad and prop shaft then you can measure plate location and do some math , you may need a 24 FURY , i ran a 210 CHAMPON other day with a 300 xs on it had trouble spinning a 25 TEMPEST loaded heavy 2 fat boys

[Montgomery]

Had to put a 23 fury on my legend to get to the recommended RPMs in the summer. I can move up to a 24 once the water temp gets in the low 60's

[EuropeanAM]

Jerzia: That's tough. Two good starting points:

1. Remove cowling and make a careful VISUAL inspection for plug wires off, bad, loose components, leaking fuel, etc.

2. Audit any BOW weight changes for increases and add WEIGHTS in the rear compartment to bring your boat back to matching the weight of your lead-acid batteries. Lithium really hasn't been approved for these, and one commonly missed point is that the substantial loss of weight can made for a considerable amount of difficulty in the performance area.

[jerzia]

Jerzia: That's tough. Two good starting points:

1. Remove cowling and make a careful VISUAL inspection for plug wires off, bad, loose components, leaking fuel, etc.

2. Audit any BOW weight changes for increases and add WEIGHTS in the rear compartment to bring your boat back to matching the weight of your lead-acid batteries. Lithium really hasn't been approved for these, and one commonly missed point is that the substantial loss of weight can made for a considerable amount of difficulty in the performance area.

Visually everything "looks" fine, nothing out of the ordinary, no leaks, loose wires etc. After adding lithiums, I did move all the weight I could to the rear. I'm about 50lbs lighter than I was before. I could add a wake board ballast bag in the rear to get the 50 back, but even then, it seems low to be 7-800rpms off.

[1ranger487vs]

Are you comparing rpms at the same time of year. Summer to winter?

[jerzia]

Not really, boats up here take a nap each winter.

[EuropeanAM]

Toss a double-bagged sand bag, or some other weight as far aft as you can (ultimate way is to put it in the battery compartment). If you've got an AGM battery still and it will fit in there for testing, set it in and go run it to record what difference it made.

Hard to explain but in practice, for every 10# you take out of the rear, the boat reacts like you added 40-50# to the bow.

[jerzia]

Toss a double-bagged sand bag, or some other weight as far aft as you can (ultimate way is to put it in the battery compartment). If you've got an AGM battery still and it will fit in there for testing, set it in and go run it to record what difference it made.

Hard to explain but in practice, for every 10# you take out of the rear, the boat reacts like you added 40-50# to the bow.

Wow, didn’t realize it was that big a difference. One thing I did check today and makes me curious, I put a torque wrench on compressor tensioner, and when it broke at 70in lbs, it had only moved about an inch into its travel. Could that be a problem?

[JOE54]

its good then you dont want it to bottom out and not obtain 70 in lbs first

[jerzia]

Well I found something very interesting. In order to get close to 3.5” prop to pad, Atlas hydraulic jackplate needs to be at 3/4 or more of total up ram travel. I ran it like that today for a short distance, and easily gained 400 rpm’s and higher water pressure without going WOT. This leads me to believe my motor is mounted too low. It is mounted in the top hole of three. I think raising it would get the plate in a more usable range as well as raising rpm’s. I was amazed how differently the boat handled, and how much less trim was needed to get the bow up and moving. Before going any further, I thought I would ask if it seems like a reasonable deduction, and if so, should I raise it up one hole, or two? IMG_1138.jpeg

[EuropeanAM]

You want the jackplate to have the firmest footprint on the transom that it can. Yours appears to be close to that, you may be getting into top cap cover, etc. if you raise the transom side.

Where it the ENGINE mounted to the PLATE? Which hole?

[jerzia]

You want the jackplate to have the firmest footprint on the transom that it can. Yours appears to be close to that, you may be getting into top cap cover, etc. if you raise the transom side.

Where it the ENGINE mounted to the PLATE? Which hole?

Transom side wasn't the issue since there are only one set of holes there. I was talking more about motor to plate. In order to get close to 3.5' P to P, jackplate rams are 75% or more at the top of the travel, leaving not much left to raise up. I was thinking if I move motor up a hole or even two, 3.5" would occur when much more of the rams were in the plate.

[EuropeanAM]

I usually try to mount engine to where it's going to place the jackplate at "roughly" the middle of it's travel when at best performing height, UNLESS the customer specifically requests something different due to where or how they operate.