Motor bogs down too much with people in boat

[Muppet]

It's a 1968 150 hp merc, on a 17foot switzer. Alone by myself it's a rocket, but once I put 4 people in there I have one hell of a time getting it to get power and get out of the water, I have to trim it way up, almost taking the prop out of the water to get the rpms up then trim it down as it starts to speed up. When I give it full gas with a full load of people it gets to about 2k rpms and just sounds like it's getting to much gas, or not enough or something. It has the automatic timeing advance and I think that might be advancing it too much for the rpms I am getting. Any suggestions?

 

[Moody Blue]

Re: Motor bogs down too much with people in boat

Muppett, instead of trimming the motor out you should be trimmed IN all the way to get the boat on plane the quickest. Trimming out will push the bow into the air and the stern into the water and will take forever to come out of the water.<br />Are you reading the 2K RPM's from a tach or guessing ? If you have a tach what is the WOT rpm's ? You might be able to change out props to give better hole shot performance but it will depend on the current RPM.

 

[JasonJ]

Re: Motor bogs down too much with people in boat

I wasn't aware they made a 150 horse motor in 68, I thought the 125 was the largest at that time. Maybe you have a 78? Anyway, sounds like a prop swap is in order. Once on plane, does it perform well? Is it getting at least into the 5500s at WOT when on plane? You might have to swap props, and get trim tabs or some other aid to get the stern up more quickly. Or, you may just need to work on your technique. Like has been said, you have to trim all the way in, punch it, and when on plane, trim out and throttle back to your cruising speed. Good luck...

 

[joblo33]

Re: Motor bogs down too much with people in boat

You might be able to get away with just adding some hydrofoils on the leg to get to plane quicker.<br />Eric

 

[Muppet]

Re: Motor bogs down too much with people in boat

Once the boat planes it moves fine in the water, not 100% sure on the RPMs, the tach isnt hooked up atm. BUt will get that back together soon. It has a 17 pitch on it now, brand new too. And ya it is a 68 150 horse, checked the serial #. I tried to keep the prop down far in the water but it just sits there boging out. Shouldnt a 150 hp motor with a 17 pitch be able to push a 17" boat with 4 people? It can hit about 40 with 4 people. About 45 with just me. So about 5mph faster with 700lbs less.

 

[Laotzu]

Re: Motor bogs down too much with people in boat

I have a 50 on a 16' aluminum. I can hit 24with just me and 20 with 6 adults. With the load it takes a while to get out of the hole, but once up I trim up and get up the speed....slowly. The rpm's are about the same...4700 at top speed. I think your right that you should do much better than your doing with 3x my hp. Getting up on plane is the key, I have the heaviest sit in the bow to help planing.<br /><br />Jerry

 

[AMD Rules]

Re: Motor bogs down too much with people in boat

Muppet, out of curiosity what is the serial number of your motor?

 

[timmathis]

Re: Motor bogs down too much with people in boat

Muppet, Hello sorry to hear that your merc is not running up to par. I have A 1975 1500 150H.P. Not long ago mine was doing the same as yours. I had to lift it up to get my rpm's up also. And with 4 people it was A real strain on it. I found out that it had 2 bad plugs and the timing was off. With A tune up and linc & sync It runs 100% better. So I would check your compression, plugs, timing, Fuel filter , fuel pressure, cap, wires etc. And I think that you will find your problem. Also you said that you have A 1968 150 H.P. Mercury did not make A 150 H.P. until 1973. Post your serial # and I can help find out what year it is. Or you can go to oldmercs.com and look it up yourself! Good luck and let me know if you need anything else. I hope that this helps you, Tim<br /><br />P.S. A lot of people make the mistake of their motor year by the year of the boat. I did. It's not always the same.

 

[joblo33]

Re: Motor bogs down too much with people in boat

Its not a Merc 150 as in 15hp is it? lol jk

 

[timmathis]

Re: Motor bogs down too much with people in boat

Eric B,<br /> You like those 1975 Mercs I see.<br /> Good year!

 

[joblo33]

Re: Motor bogs down too much with people in boat

Ya, I'd prefer a couple 76's though. These 75's are nice but they're the last year with the dreaded point and condenser system which is now a discontinued part. I'm kinda glad the 65 has a blown rod and is now in the shop where I have a donor late 70's powerhead.

 

[timmathis]

Re: Motor bogs down too much with people in boat

Yes points can be A hassle. At least my 1975 150 dont have points!

 

[joblo33]

Re: Motor bogs down too much with people in boat

Oops, typo, I meant cap and rotor system.

 

[AMD Rules]

Re: Motor bogs down too much with people in boat

Topic: What year is this motor?

 

[RandyJ]

Re: Motor bogs down too much with people in boat

Wow...sound like you guys are running the same era of old merc's that I've got...at last count I was down to 4 of the 50 hp mercs and two 650's from the 1968-1978 range. Great when they're running but ugly when they're not up to par. My best is a 1978 50 hp on a 15ft alum v-hull and it will haul azz..no speedometer but I'd guess that it's well over 40 mph. Jerks a 110 kid out of the water on skis with 3 or 4 people in the boat.

 

[Laotzu]

Re: Motor bogs down too much with people in boat

Randy, what am I doing wrong? As I noted, I can break 24 with a '91 50hp with about the same size/type boat. I thought I was doing good til I read what your's can do. You must wax the hull with space age silicon.<br /><br />Jerry

 

[joblo33]

Re: Motor bogs down too much with people in boat

I can pull a wakeboard with two people in the boat with my 1975 50. It's just a little more challenging to get up than with my uncles 130hp boat.

 

[timmathis]

Re: Motor bogs down too much with people in boat

Thanks AMD 74 is O.K.

 

[Muppet]

Re: Motor bogs down too much with people in boat

Ahh whops, ya the boat is a 68, motor is a 74.

 

[JasonJ]

Re: Motor bogs down too much with people in boat

I just got down helping a friend today that has a 78 115 hp Merc on a 16 foot bass type boat. Thing was doggy as heck, would sometimes get up on plane and cruise, not getting past 4000 rpms. Other times just would not get up on plane at all, just doggin and boggin. He rebuilt the carbs, new fuel filter, cap, rotor, all that jazz. it was better, but was still real doggy on holeshot, and got to maybe 4700 rpms. Then we replaced the 19 pitch prop with a 17 pitch prop, and the difference was dramatic. Almost 6000 rpms with two people on board, engine ran real smooth, and it popped up on plane right now. I would not have thought a prop switch would make that big of a difference, but in this case the difference was huge.