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I am having an intermittent problem with my 1999 Yamaha ox66 250. The boat has twin engines, starboard engine is running perfectly but port engine has been having this problem on and off. When the engine is started, it will not come down from its high idle and when the engine is given full throttle and it is very difficult to shift the engine into forward or reverse. it will not fire plug #5 and will only reach 4000 rpm WOT (other engine does 5200). This problem will come and go, but it has become much more constant recently. On the last ride, the engine did this for 15 min (high idle, hard shifting forward and reverse, and would only reach 4000 rpm WOT) and on the way back to the dock, I noticed when I shifted the engine into neutral it began to idle at 700 rpm like normal. Turned back around and went for a ride and the engine performed just like it should and reached full rpm. Let the engine sit for 30 min, went back out to try to duplicate and the problem started all over again. I know that it isn’t firing #5 because the plugs were recently changed, and after an unsuccessful ride to get the boat above 4000 rpm I pulled the plugs and cylinder 5 had not been fired. Test that plug while cranking the engine and sure enough it was not getting spark. Swapped the coil from a known working spark plug and it still did not work telling me it isn’t a coil issue. I also swapped the CDI boxes between the engines and that did not have any change. I do not think this is a fuel issue because when the engine randomly runs normal, there is no problem with the fuel delivery. Any help would be appreciated!