1988 Merc 90 hp cutting out

[maxthedog]

My merc 90 hp (three cylinder) has a strange problem ... every once in a while it loses power or drops a cylinder, not sure which? It will be running just fine then out of the blue it won't rev over 3000 or if I'm running over 3000 it drops to 3000. This happens even when running below 3000... seems like it's dropping a cylinder but I'm not certain. This condition may last 10 seconds or 10 minutes, then it runs fine for a while. May run good all day but then act up the following day. Where do I start to troubleshoot? Electrical or fuel? Any other advice? Thanks

 

[maxthedog]

Re: 1988 Merc 90 hp cutting out

My merc 90 hp (three cylinder) has a strange problem ... every once in a while it loses power or drops a cylinder, not sure which? It will be running just fine then out of the blue it won't rev over 3000 or if I'm running over 3000 it drops to 3000. This happens even when running below 3000... seems like it's dropping a cylinder but I'm not certain. This condition may last 10 seconds or 10 minutes, then it runs fine for a while. May run good all day but then act up the following day. Where do I start to troubleshoot? Electrical or fuel? Any other advice? Thanks

Can a stator, coil or switch box act up intermittently? I failed to mention when the boat is in my garage all the fuel in the filter bleeds out the carbs and into the air box ... can these problems be related?

 

[macstang99]

Re: 1988 Merc 90 hp cutting out

ive got a 70 merc 800 that had the same problem. ended up being a loose spark plug

 

[maxthedog]

Re: 1988 Merc 90 hp cutting out

When the motor started acting up the first thing I did was replace the plugs. That didn't cure the problem.

 

[andy6374]

Re: 1988 Merc 90 hp cutting out

The intermittency of the problem is a tell-tale sign that it's probably ignition related. Take a spark test when the motor starts acting up. Do you have a manual? Have performed any of the resistance test on the stator and trigger.

 

[maxthedog]

Re: 1988 Merc 90 hp cutting out

Just recently got a Seloc manual for this motor. Haven't preformed any resistance test because I don't have any testing equipment. Just started reading the chapter on ignition. I guess I'll have to buy an ohm meter (is that correct) and a spark tester. I'm not sure how I'm going to test it when it acts up in the water.