yamaha f90 wont start

[buckytheman]

I have a 2008 yamaha f90 that was sunk. i have replaced the starter and relay and the trim relay. I cleaned the injectors and replaced the hp fuel pump. the motor runs great and i have put approx 100 hours on it. if the boat sits unused for more than a couple weeks, it doesent start, hard turning over(like its got too much ignition advance?) and backfires blowing flame out the leg. last time i took the plugs out , turned it over, put the plugs back in and it started. not this time. Any ideas? do i take it in for diognostic test? help please!

[boats.net]

Could be flooding, VST overflowing back through vent or injectors stuck open. Could be loss of spark to plugs and if it sunk probably have a lot of corrored wire connections.

[sachin2021]

Also check all wiring. Am guessing that motor sunk with boat. Start at the battery anud all 5he way to the starter as well as thermosensor. Also pull your fuse box out and clean off all corrosion. Also check the wire running up to the starter relay from the fuse box. Might be corroded. Went bad on mine.

[buckytheman]

all the connections are good, gonna try cleaning the injectors again.

[buckytheman]

gonna go over the fuse box again.

[sachin2021]

Also disconnect your thermosensor and see if it will start. A bad thermosensor will also cause a no start/intermittent start problem.
If you have a new starter, starter relay, fuels pump etc than you can rule out those being the problem provided the compenents were installed properly.
If you have backfires spark is there but the backfire is due to flooding. Could be a stuck injector but more likely trying to start it with fast idle and repeated cranking. I suspect corrosion as my F150 went down and we got it going within a day and thought all was okay till I had a problem like what you are describing. Turned out to be the wire from the fuse box to the starter relay. After that a no start condition that was traced to a bad thermosensor after much experimentation. Hope all goes well.

[buckytheman]

what is the thermo sensor? and where is it? the stator is a bit rusty and one of the pins on the rectifier is corroded. my buddy has a stator and a rectifier for me. im looking for the whole harness part # 6D8-8259-30-00 new or used, from a f75/f90 2006 and newer. anyone know where i could find a used one or a deal on a new one?

[boats.net]

Number 1 in this link is engine wire harness, 2006 and Later 4-stroke F90TXR Yamaha Outboard ELECTRICAL 3 Diagram and Parts