question I might pose: is there any tilt/trim adjustments?
you might not be getting the thrust off the engine pushing the right way
Art

there are about six tilt adjustments plus the shallow water mechanism which raises the motor more. I have tried them all and just do not get enough of the boat out of the water to plane and the motor does not reach a high rpm under the larger load of two people.

I was most concerned about revving too much or that maybe an 8-inch pitch would be needed or that 15 horses just won't plane two men.

DT15C getting on a plane

I have an 1974 14’ Alumacraft boat and noticed right away the transom height wasn’t high enough for the outboard. I secured a section of 1 X 2 pressure treated wood to the top of the transom. Now when hanging the outboard the anti-cavitation plate sits just ABOVE the drain hole in the transom. Your requirements may be different but the goal is to raise the outboard to this correct level. This reduces a lot of unnecessary drag and helps top end performance as well.

Also try moving the trim pin all the way IN towards the transom. If your 10 in pitch prop won’t plane you guys off after raising the motor and trimming all the way in THEN it’s time to pick up a prop with less pitch. Stick with the same diameter (I’m assuming 9 in diameter here) but less pitch. You can also have a prop shop remove pitch from your existing prop for a nominal fee usually - but a second prop is always a good idea! Keep the 9 X 10 when you’re by yourself and switch to a 9X9 or 9X8 when you take you buddy along. However none of this will help much if too much lower unit is in the water! Take the time to set engine height correctly before you spend money on prop changes.

One last item: if you’re worried about over-revving when by yourself simply reduce the throttle a touch after you get to your cruising speed! Outboards are way more tolerant of over-revving than they are to overloading (not able to reach peak RPM) Let us know how you make out, ok?

been doing lots of reading and read that height of the motor is critical. I remember when buying it used the shop guy put some wood spacers on top of the transom to get the long shaft a bit higher. I should check that height after fixing the carb.

an 8 inch pitch seems like a 20 percent gear reduction which sounds like a lot.
a 9 inch seems like 10 percent and not much different.

eta
another thing I am seeing is hydrofoils seem to help under powered boats get on plane. maybe that should be tried first.

first look at the cavitation plate, flat plate above the prop. that plate should be at, or slightly above the bottom of your boat. Then, when on plane that plate should be riding the surface of the water, if under water, raise motor 1", and try again.

If you think it is more than an inch below water raise it 2". Then try again.

Good luck.

cabela's had the se sport 200 hydrofoil on sale this week for 40 bucks so I ordered it.

finally got the carb cleaned enough to idle as noted in my other thread. ten years sitting had completely closed a hole in the jet at the top of the carb.

i'm ready to put the motor back on the boat but may wait and install the hydrofoil first and it is currently shipping. I hope the shop guy originally mounted it at right height since he drilled the transom and bolted the motor on.

I would be very cautious about the use of any treated timber against an aluminium hull. Especially any of the green treated timber (treated with CCA) due to the copper in the treatment. Likely to cause severe corrosion issues due to electrolisis.

tnadeau,

so did you raise it the 2-inch or the 1-inch dimension?

I think my stock prop is the 9-1/4 diameter.

I seem to remember when trying to plane two guys I was able to trim the motor to washing out in the air. seems like I was pretty close to the correct height ?

I've read several times on the net that Suzuki's have rev limiters so going too high is not a major concern?

Your model dt15, may not have the limiter the newer motors have, but it may have some rev limiter if you have the tach and monitor for the Suzuki motor connected?

Still the first step is the height of your motor on the boat.

Good luck. Post back how its going when able to let us know how it's going.

my motor plate is even with the bottom of the boat. there is not much room to raise the motor any without the motor clamps getting no purchase on the transom. I would need to extend the transom up instead of using shims like I have now at about 1 inch raised.

or maybe the bolts through the transom are enough? there's at least 2 inches above my bolt holes that it could be raised.

seems like some form of transom reinforcement might be needed. I understand the concept of adding height by drilling into the top of the transom for something like square tubing.

the second idea is adding height by attaching a new piece of plywood to the transom that goes higher and maybe add blocking above the transom for clamping.

I went through the hustler prop wizard and they recommend a 9 x 9 prop compared to the 9-1/4 x 10 I have on my machine.

i bought a 9x9 hustler prop and will pick up the hydrofoil today. i want to see the effect of each item separately.

i will try the hydrofoil first since it should raise the rear of the boat and i want to see if it reduces performance or it helps. i also won't have to lean so far over the back of the boat to see it's height/depth while on a plane.

i expect the prop will still help with heavy loads/proper rpms. i also like the idea of having a spare prop finally.

i don't want to modify my transom to raise the motor. mainly for fear of damage while trailering.

i picked up the hydrofoil from cabela's and started thinking about winter and my boat sitting in the driveway all winter getting exposed and i am considering delaying any more boat work until spring. getting the motor running was a good move since it took a long time to figure out the problem. the new parts will go on quickly in the spring and i can store them inside away from all the freeze and thaw cycles of one winter.

i may not be back here so thanks for all the ideas...