Evinrude 90 Cylinders not Firing


I have a '96 Evinrude 90 that is only running on top two cylinders at start up.  After about 5 minutes on the lake it will backfire quietly a couple of times then bottom two cylinders will kick in and then I have full power to plane.  It is then fine the rest of the day. About one in five times the bottom two will never kick in at all, all day. 

At home troubleshooting, the engine will start with top two cylinders spark plug wires attached, bottom disconnected, but will not start with bottom two connected, top disconnected. 

My first thought is that is must be the bottom carb, but I do not see any exterior adjustment screws- without taking the air box off.  Do I need to adjust the bottom carb, and if so, where and how?  I am decent at tuning by ear, but is there a standard number of turns to start with? 

Thank You,

It is most likely the power pack. On those engines you may need to replace the timer/base/OIS at the same time.




Please submit whatever questions you have to IHRTechTalk@yahoo.com.  All questions and answers selected will be displayed on this page as they come in.  Note: though all boaters are welcome, priority may be given to I.H.R. members.  Randy can not be held responsible for any advice given.  Though his information and expertise is second to none, he has no control over what you do with your boat.  It is up to you to boat safely and act responsibly, and his advice is only to be used as a guidance for your high performance boat/motor of which you are the one responsible for the risks involved.

Mark C.


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