Mariner 175hp running badly under load

Jedrobert

Recruit
Joined
May 8, 2018
Messages
3
Hey guys having a couple of problems with my Mariner 175/135hp 2 stroke motor.

Bit of background on boat.
purchased it about a year ago it has a 135 cowl on it but it's got 175 stamped on the block. I'm guessing it's around a late 1990s model. Took it out once tilt trim motor burnt out and didn't have time for it untill recently.

Replaced tilt trim motor from an American site. Installed it and it's got a small leak from the seal on the motor. I purchased the exact same part number so I'm not sure why it's still leaking any ideas? Was thinking about bleeding it and trying to make a new seal from rubber is this a bad idea?

Now the real problem.

1st outing - So I took her out and she ran really good but at the top end it starts to bog down and won't go as well as I know it should.

2nd outing - motor was shaking and not running very well so I purchased new thermostats and impeller installed them.

3rd outing took her for a 30 min trip to a reef. On the Way out she'd be going and then I'd back of the throttle a little then she would die. I'd start it again and shed fire straight away and away we'd go again. Idles perfectly but still has the slight shake to the motor. On the way back we were cruising along full throttle then all of a sudden she started opening right up and going to full power. My mate was standing up and almost fell over she pulled that hard. So we took her home purchased a really good fuel water filter replaced the fuel lines and pulled the carbs apart gave them a clean and put her back together.

4th outing Took her out to a freshwater river to test her out idled perfectly started with no revs motor still had a slight shake but I'm under the impression it's how it's always been. Never took to much notice so not 100% sure. Got on the plane nicely although it still won't get the power I experienced on that previous outing.

5th outing purchased a fuel additive that claims to clean the heads and carby and put a 12v fuel pump on to see if it's a fuel pressure problem. She ran really badly and didn't have much power then all of a sudden she started going a little harder. Found a spot to fish then when we were finished headed back anc she was not producing much power at all..

Does anyone have any ideas what it could be?

could i have done some damage in a previous outing having a bad impeller and blocked thermos?

could a coil pack not be working properly?

I replaced the the spark plugs when I first purchased her should I replace these again?

Shoukd i I run a can of sea foam and try decarbing?i live In Australia does anyone know of an alternative in Aus?

The prop has a few chips and small folds on it where it's hit things could that also be the problem? My next thing was to pull it off and check for any problems and regrease. And file down the fold where it's hit a rock from previous owner.

Thanks in advance for any help you could give me cheers
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
39,267
Do a compression test.----Then see if spark will jump a gap of 1 cm on all 6 leads.-----That test may find a bad coil or switch box issues.
 

Tassie 1

Chief Petty Officer
Joined
Apr 13, 2018
Messages
584
G'day,
as well as the excellent advice above check the spark plug leads fit properly on the plugs, not coming loose when running etc etc

also check that the leads themselves haven't been rubbing on the block and causing a short etc etc at different speeds/ water conditions

definitely pull the plugs and check their condition and appearance,

another good tool today is one of the little digital temperatures heat gun thingees, take the engine lid off after a run and just point it at the donk and that will tell you if it is overheating despite the impellar pumping water,

Did the old impeller have all the vanes still on it?
if not, did you find all the olden broken bits of rubber that can block passages etc etc

haven't seen seen sea foam or a alternative to it here in Tas or Vic, when we lived there yrs ago,

my son has a '98 175 merc that has a slight vibration at trolling or lower speeds, it drives him nuts but l barely know its there,

also buy a manual for it of ebay, hard copy is my preference,

can't help with the trim problem, never had that problem with them in around 20 donks, just lucky l guess,

​​​​​​​cheers
 

Jedrobert

Recruit
Joined
May 8, 2018
Messages
3
Hey guys sorry about the late reply works been flat out.
thanks for your replies guys!

I did a compression test and it came back with
1 - 80psi

2 -90psi

3 - 70psi

4 - 90psi

5 - 90psi

6 -90psi

Only one of the leads spark would jump the 1cm gap. Tested them and only one lead was good. I pulled the coils and only 2 of the six didn’t have cracked magnets.

Im thinking because the motor is so old the head might need a rebuild will this fix the compression problem? Or could I get her running and run Seafoam/ powertune through the carbs while running and give her a good clean out before a rebuild?

also if someone could help me out the serial number is 0d166539 I can’t find anything online to find out what year/model it is


P.s I’ve never learnt much about engines so I like to challenge myself and learn new things so the work/time doesn’t scare me
 

Dukedog

Captain
Joined
Oct 6, 2009
Messages
3,496
those numbers, if accurate (need another gauge to compare) its very, very tired.... needs some serious help.. probably in all areas including all 'lectrics….
 
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