89 Merc 175

[Cold Sooner]

Great forum, thanks.<br />My boat is a 1973 Terrybass with a 89' Merc 175. Problem is that once she gets on plane the front of the boat seems to enjoy bouncing up and down. I was told trimming the motor up should help keep the bow down. I tried this while in motion and the motor does not respond. When I trim it before launching it just gets sucked back down. If anyone could point me in the directon of some things to check I'd be very thankfull.

 

[JB]

Re: 89 Merc 175

Howdy, Sooner. Welcome to the board.<br /><br />Your boat is "porpoising", and it sounds like your power trim is leaking, too, but there is a problem here that I don't understand.<br /><br />The usual way to control porpoising is to trim the engine "IN", or down, to lift the stern of the boat a bit. Trimming the engine "OUT" or up lifts the bow and decreases drag up to a critical point, the point at which porpoising starts.<br /><br />First, get your power trim 'n' tilt working properly. I'm not a Mercspert, so someone else will have to suggest how to do that.<br /><br />Too much weight in the stern will make a boat porpoise easily. Double check that your boat can handle 175HP. Most of the Terrys I remember from that era were maxed at below 100HP.<br /><br />Let us know what you find.<br /><br />Red sky at night. . .<br />JB

 

[trevorcday]

Re: 89 Merc 175

The first thing to check if your trim unit is leaking down is the manual release valve. <br />If it is loose has some dirt under one of the O-rings or is damaged the trim will leak down.<br /><br />Raising the motor on the transom generally will reduce porpoising but at some point the boat will become prone to cavitating and will not be able to be trimmed up. If raising the motor doesn't solve the problem addinf small trim tabs will probably help. this is all assuming that fixing your trim problem doesn't make it go away.

 

[Cold Sooner]

Re: 89 Merc 175

Thanks for your quick replies. <br /><br />JB, I can't find the data plate on this boat so I'm not sure what the horsepower rating is. This boat is 18' and "looks" very heavy.<br /><br />Mrmerc, this boat does have a transom jack. I'm going fishing Sunday and will raise the motor up and give it a try. I'll post back my results. <br /><br />Thanks again, Andy

 

[clanton]

Re: 89 Merc 175

The T&T leak down is most likely caused by the pilot check valve seals in the hyd pump body.

 

[Cold Sooner]

Re: 89 Merc 175

Thanks guys!!!<br />Raised the motor with trim down and WOW!! Came out of the hole great and planed out very smooth. Once on plane I started slowly trimming the motor out and went from 35mph to about 50mph before it felt like it was going to start porpoising. Never noticed the motor getting sucked back down. I stopped there and just enjoyed the day going from one<br /> "honey hole" to the next. Boat ran GREAT. Bass were biting. <br /><br /> Thanks again.