Length of my Lower unit. - Too Short??

[flycaster1]

I recently bought a pretty nice 1999 245 Explorer.
On the back hangs a Optimax 225.
The boat runs strong and doesn't act like the prop is having cavitation however now and then the water pressure drops off and I have to throttle down then back up again to regain the pressure and thus silence the warning horn which I do without hesitation. I have taken long runs with this boat and all was well.
I plan on replacing the pump, etc. this winter anyway wonder if at some point in time the lower unit may have been replaced with a lower unit which is too short for the hull. If I should run a longer unit I may look into obtaining a rebuilt exchange unit and not put the money into the pump but I.m hoping the pump is the root of the problem.
The hull has the step in it between the motor mounting extension and the actual hull.
I have attached pictures and would like your opinions.
Thanks in advance.

[CLM65]

No, your motor is not too short.  If anything, it might be mounted a little low on the transom.  The cavitation plate should be a little above the bottom of the transom.  It sounds like your problem is the pump...the impeller may be slipping.

[fitz73222]

Do a waterpump, thermostats and poppet valve assembly. If you don't know the entire history of service on the engine, this is good baseline maintenance. Spend the money and get a real factory service manual for this engine, about $75.

[Capt. Bob]

You can do a quick "math" check on you motor height. Measure the length of the transom step. This setback length is what you'll use to get a good starting point for the ventilation plate height relative to the hull (not the step).

Measure from where the step starts to where the motor is mounted. For every 12" of length, you want the ventilation plate to be 1" higher than the hull (again not the step) So if your step length measured 24", you would want to mount the motor ventilation (often called a cavitation) plate 2" higher on a line extending from the hull bottom. This is a good starting point for dialing in the proper height. Actual viewing while underway will tell you if any fine adjustment is needed.

Here's a detail.
http://classicaquasport.com/phpBB3/view ... 84#p124184

Good luck.

[flounderpounder225]

Having the same boat, I think mine is on the second to lowest bolt hole, we raised it from the bottom hole because on plane the Cav Plate was a little too far below the water line.

[wingtime]

Like Marc says they are usually mounted one hole from the top hole.  Due to the offset from the step I'd say you look good.  Maybe even a tad low.  Change the pump impeller... if the motor is new to you replace the entire pump housing top and bottom as well.  If you have a gopro camera mount it on the transom and see if you can get a video of where the cave plate is when on a plane.  My 245 Explorers Johnson runs with the cav plate on top of the water when on plane.