Please help.... 1998 Mariner 50hp 2-stroke loosing power, boat shop at a loss

indebubble

Recruit
Joined
Aug 22, 2011
Messages
1
Hi,

I have a Quicksilver 4.5m rib with a 50hp Mariner 2-stroke 3 cylinder which keeps loosing power. I first took the boat out and it ran like a dream until I did a turn and then switched off, when I re-started it ran very under-powered until I got it back. I then took it straight in for a service and they shop advised me that the fuel primer had broken up inside and had caused a partial blockage - problem solved, or so I thought.

The next time out it ran really well, we went along the coast and up a creek to a pub, no running problems -the engine had been off for over an hour and coming back it dropped a cylinder. I got it back and thought that this was down to damp as there was a small crack in the cowling and may have let a small amount of spray in. I sealed this up and went out again, we were not flat out but cruised for about four miles around an old pier and then came back - coming back I did a turn (maybe not relevant at all) and then it dropped a cylinder again. I limped it back to the slip and then took the cover off and sprayed the leads/plugs with wd40 and it ran great.

Since then I have been out a few more times and it seems to be getting worse - I was conviced that it was damp as a quick spray seemed to make it better for a short while. However, I did pop out the plugs (which were replaced at the service) and the bottom one appeared to have water droplets on it so I checked fuel for contamination. My block is a one piece unit so does not have separate heads so the boat shop have told me it cannot be that. I worry that water is getting up the exhaust when I put a turn in??

I also thought it could be a dodgy coil so I swopped them around to see what difference that made. I put the bottom coil to the top and top coil to the bottom as the mis-fire seemed to be on the bottom cylinder.

I have been out on it again and was very careful of not doing any fast turns at all, and the engine packed up again - this time worse than ever. It ran on three for a very short while (2-3 minutes) and then seemed to run on only one cylinder and kept stalling. I sprayed the lot with WD40 and this made no difference. I limped it in and thought that it must be the coil.

As I said, the top coil was on the bottom and the bottom on the top but still the bottom plug was oiled up and hadnt been running - the top was fine. No evidence of any water ont the plugs. I then tried to take off plug leads and see if one made no difference to the running. This was tricky to tell as it was only on the muffs but it didn't seem to make any difference which lead was off - or all on...

I have spoken with the shop who serviced it and they don't really know. Has anyone here come accross this before? Are there any suggestions? What would be the next step in trying to diagnose it?

Any help is really really appreciated....
 

SparkieBoat

Captain
Joined
Aug 17, 2009
Messages
3,643
Re: Please help.... 1998 Mariner 50hp 2-stroke loosing power, boat shop at a loss

diagnosing a 2 stroke carbbed outboard is a very easy thing to do most times. you have to follow a certain order. follow the instructions in my sig below. I will add that if compression, spark , timing, linkage are all good you could have a failing fuel pump or a fuel line/connector sucking air, you said it started once after making a turn, so maybe the fuel connector at the engine is bad. I would recommend buying a complete new fuel line and using another good fuel tank, and see if you still have problems. there is a free guide on how to trouble shoot your electronics in my sig if you are having spark issues.
 
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