40hp big twin miss fire

[Jon_mark]

Hi, i have a big twin 40hp evinrude not sure what year it is, model No 40858? last didget might be a '0' or 'd' . ser c558027. anyway after about 30 min the engine will only run on 1 cylinder,(sometimes kicks into 2)done the plugs and coils and am now stuck for ideas...please help.<br />Thanks<br /><br />Jon

 

[JB]

Re: 40hp big twin miss fire

Howdy, Jon.<br /><br />Do you know if the "dead" cylinder is getting spark? Easy enough to check by pulling the plug wire and trying to get an arc to the block.<br /><br />Have you confirmed that the water pump is functioning properly?<br /><br />This sort of symptom is usually related to heat, either the cylinder is overheated and trying to seize or some component in the mag system is failing when hot.<br /><br />Just to eliminate the fuel system, pump your primer or spray extra fuel into the carb when it misbehaves.<br /><br />Good luck.