yam 90 dies at 4500 rpm
i've been having some trouble recently with my 1999 yamaha 90 hp 2 stroke. it starts fine, idles fine and up to 4500 rpm the engine runs sweet as a nut. when rpm goes above 4500 it will run fine for anything between 1 and 5 mins before it dies. it doesn't cut out completely but the rpm drops and it sounds like its running with a cylinder down. when this happens i return throttle to neutral, wait a few seconds for the revs to come back to idle and check its back to normal by raising the rev bar and after 1 or 2 blips of the rev bar it fires as normal and away i go again sweet as until the 4500 rpm is exceeded.
i read a similar thread on here a couple of weeks ago but all the replys pointed to fuel supply problem and i am sure this is not, i have a 22l hulk reserve tank on board and it still does it with that attached so ruling out problems with the main tank, the carbs have been cleaned and rebuilt with a full yamaha service kit, a new internal inline fuel filter fitted, all fuel lines blown through and a new set of spark plugs. to be fair all this has greatly improved the starting, idle and running but still got the same problem at higher revs.
so after doing all the work on the fuel system my thoughts are with the electrical system but i'm a bit reluctant to buy any rectifiers, coils etc without being sure they are the problem so i was hoping someone on here might be able to point me in the right direction.