90 hp mariner has no power

[mc3po]

this is a late 80s 90 hp mariner with no distributor. It will only turn 3400 rpm maximum. It acts like it wants to go from time to time. I had the carbs rebuilt and put new water seperator and filter inline as well. I also cleaned the fuel pump screen. It is getting fuel. It will idle fine for a while and then it starts acting like it is either dropping a plug or picking one up. It jumps around a lot. I really don't have a clue where to go from here. I am sure that 3400 rpm on a 90 hp is way too low. any suggestions would be appriciated greatly. thank you in advance

 

[njrextreme]

Re: 90 hp mariner has no power

My guess would be to start with a spark check on all 6. If it lost a switch box, you are firing on 3 not 6. Compression check would be next if it has good spark.
If it is spark, it could be three or four diff. things.
Nick

 

[arsenalpsu]

Re: 90 hp mariner has no power

You need to check for spark and compression. Look here for testing your ignition http://www.cdielectronics.com/downloads/troubleshooting guide/ & compression should be +/- 15% of each other. If you plan to do your own work on this I would highly recommend you purchase an OEM Mercury manual. You'll need a multimeter with and a DVA adapter, which you can make (search here for the plans) or purchase one. All repairs on this motor can be done by someone who has any sort of mechanical common sense. I would be you're missing spark on atleast 2 plugs. Don't forget to test your spark plugs, should .5 OHMS or less.