50 hp Mariner 4 Stroke - intermittent problems

Black · 22 April 2010, 11:20

Bought another boat at the weekend - unfortunately not a RIB, family duties needed some shelter for the little ones.

I tested the boat before purchasing and the engine ran well.

Upon getting the boat to Salcombe, the engine seemed to run very well, idled nicely after launching and ran perfectly for 40-50 mins of displacment speed cruising in the estuary.

When throttled back to slow speed after 50 mins, the engine coughed and spluttered and then cut out. I managed to start the engine again, and it would take revs out of gear, lifting up the flap on the throttle box, as soon as gear engaged it would go up to idle and then cough and splutter if any more revs added. As quick as this happened it passed, only to splutter a couple of times on the way back to the slip way. Needless to say the wife wasn't impressed!

The fuel tanks were new, with fresh fuel that morning - any suggestions of other things I should look for?

Downhilldai · 22 April 2010, 11:22

Fuel tank vents?

Black · 22 April 2010, 11:29

I did check that, they were nicely open.

The fuel tanks are 25 litre plastic jobs, in a locker under the deck.

There is a built in fuel line connecting them to the engine, the bulb on this never seeks to get as hard as the one on my SIB does, is this something to worry about?

Downhilldai · 22 April 2010, 11:33

It sounds like fuel starvation. You could try having someone pump the bulb while you're driving it. If it runs ok at full throttle, then you may have a problem with the fuel pump, fuel connector(s), or fuel bulb.

Searider · 22 April 2010, 13:45

Had a similar problem with a 90 Mariner 2 stroke a few years ago.

The timing is advanced with throttle position and should return under spring tension. With the boat having been unused for some time this mechanism partially seized and would not return under its own spring pressure.

Have a look under the hood and see if theres a plastic arm that's pushed by the throttle cable. Does it return when the throttle is returned to the slow position?

Black · 22 April 2010, 13:58

Sounds like something to check out - although when I was having problems it wouldn't accelerate/pick up revs at all, just stuttered away and felt like it was going to stop.

Definitely going to check that arm out..

outboardtech · 23 April 2010, 07:24

hi , is the primer bulb a genuine quicksilver one , If its a TEMPO one get rid of it ?

Searider · 23 April 2010, 12:27

Quote:

Originally Posted by outboardtech

hi , is the primer bulb a genuine quicksilver one , If its a TEMPO one get rid of it ?

I'll second that. Had that problem as well.