Boat Trim/Speed

I was out in my boat last week on bago.

17ft Starcraft Alum deep V. I recently added an 8hp kicker (4 stroke). I lost about 5mph, I thought that was quite a bit, at least more than I expected. The boat has an '04 115hp 4-stroke. I got about 40mph out of it before the kicker.

Wednesday I was up north, it started to rain. Put everything away and go. Full throttle, 7.5mph. Obviously somethings wrong...

It won't trim up or hold trim under power. I trimmed it up and as soon as I hit the throttle, the motor came back down to the transom. It trims up/down fine when not under power.

I haven't really looked at it yet, but any chance it's just low on oil? Leaky seal or such? I know those trim units aren't cheap.

Any ideas or suggestions are appreciated. Thank you.

I had a motor once with a similar issue.  Turns out some check valves were shot.  The parts were hard to come by and it would have taken 10+ hours of work to repair.  I sold the boat with full disclosure.  I think the guy repowered the boat and used the motor for parts.

Well, the oil reservoir was full... 

I'll try disconnecting the switches, but I don't think it's that (guessing) since it works fine until under power. I am guessing bad seals, or something along those lines.

I didn't touch any of the wiring and the boat was completely rewired last fall.

I'm no help there Jared, I've never had to buy any...

Do disconnect the trim switches like discussed in my last post.  I'm very interested to see if that solves it.  

Plmlk,

Thanks for the reply, it very well could be multiple issues.

I trimmed the motor up, let's say "half way" look back, go up to full throttle and the motor comes back to the transom.

Under full throttle, if I try and trim up even a little bit, the motor will not move. As I said, it does however trim up/down fine when not under power.

The motor sounds fine as far as I can tell anyways.

What kind of fluid does it take? I've seen about 100 different answers online.

I'm not sure I understand.  7.5 mph with a 115 hp motor trimmed all the way down???  That sounds like more than a trim issue.  

At any rate, I don't believe it is your hydraulic cylinders, air, or a leak, as if any of them were the cause, it wouldn't trim up whether you were in the water or not - the issue would be consistent. 

I would suspect the trim button in the binnacle control or on the side of the outboard cowling.  A few years ago my motor would trim up for no reason at all.  It didn't matter whether I was going 40 across the lake, or parked in the garage.  The trim switch would occasionally short out, and my motor would trim up.  

To verify, try this.  Trim your motor up, then pull the wires on the trim switch in the binnacle control as well as in your motor.  Then engage the motor and see if it stays trimmed.  If it does, you have found your problem - the trim switch.  If it continues, you would have to have a short in your wiring harness somewhere.  

Another thought.  You mentioned you recently installed a kicker.  I'm assuming you installed a single hydraulic cylinder for the kicker???  If so, it may have something to do with that.  Whenever something goofy happens, it may be related to recent work.  

One last thought.  You mentioned it was raining.  When the trim switches start to go, they may have lost their resistance to water, and the water may be shorting out the switch.  

Air in the hydraulic system could cause "spongy" operation. Or, bad check valve which would allow motor to drift down after being raised. This would happen if you were stationary or under power.