'99 50 HP 4 Stroke Merc loosing power/misfiring?

[fingaz]

i have a 1999 16' alumacraft bass boat w/a 50 HP 4-stroke Merc on it and recently I have been having this problem:

When I start the engine, she sounds great... however, when the engine gets warm, it sounds/feels as though I am loosing one of the cylinders. You can distinctively hear the engine studdering or spuddering as it sounds like only 3 of the 4 cylinders are firing. Every so often, I can hear a click/tick sound... at that moment its like something clicks in the engine and and that fourth cylinder works perfectly again.

I have no idea what it could be as I am limited in my knowledge of engines.

People have said that the engine may be getting choked out... that I may need a new air filter or fuel filter... or that the choke may be stuck in the on position/or it keeps sporadically choking the engine making it not run smoothly.

any tips or comments appreciated.



p.s. - I will be replacing the fuel filter/air filter and have already replaced the spark plugs. Engine has has a tune up in the spring - new oil/filter, and everything greased and lubed. Will update after I put the new stuff in.

 

[fingaz]

Re: '99 50 HP 4 Stroke Merc loosing power/misfiring?

one more thing... engine has been running rough like this in the lower rpm range. When I push the throttle higher, about halfway up, it seems like the engine starts to run at full strength and sounds great. then again.. when i lower it down.. it starts to misfire/get choked up again.

via GPS... I found that I got up to 30 MPH last season. This year, the fastest I can go is 20mph. So there is def is some major power loss even when the engine is running at the higher rpm when i think it is sounding good.

 

[dexterd]

Re: '99 50 HP 4 Stroke Merc loosing power/misfiring?

check your stick coils and your plugs again. put dilectric grease on your electrical connections also.

 

[bloodyfinechap]

Re: '99 50 HP 4 Stroke Merc loosing power/misfiring?

Hi Fingaz, I have the same engine but branded Mariner. I have the identical problem to the one that you have written about. If I start the engine from cold and don't push it too hard it runs perfect. It can sometimes run perfectly well all day but than all of a sudden it will start to misfire for no apparent reason, if there was a pattern it seems to be when I am pushing the engine quite hard. When you drop down to lower revs it misfires and will continue to do this for the rest of the day. If I open the throttle up and bring the boat up to planning speed the misfire goes away and the engine runs perfectly. Once I drop the revs back down to slow speed the misfire returns. It is particularly difficult to get the engine running if you switch off as although the engine will start you have to ram the throttle up quickly to get the boat going or it will just stall. I have had this problem for over 2 years now and no one seems to be able to find out what the problem is. The odd this is that when the engine is missing and then I finish using the boat that day, I can go back to it the next day and it will run perfectly again. Question - did you ever find out what the problem was with your engine, or is there anyone out there who could help me get to the bottom of this? thanks bloodyfinechap