F90 Does Not Start???

[rougeaut]

Start n Stall Out

recheck your compression AFTER making sure the TDC is correct AND the cam marks line up correctly.
the F90 is an interfernce motor and WILL bend valves if cam timing s off.
it also doesnt like to start if the throttle is advanced.
check rail pressure wen it dies.

Hi I was sure to turn the motor over by hand 10-12 times to check and see and listen that nothing was interfering. I will recheck the compression tomorrow as you mentioned.

I rechecked the fuel pressure on the rail today and it was at 43 PSI with the key on and around 40 when it turned over and starts and runs for a few seconds, after it dies the pressure stays solid at 40-42 PSI for a few more seconds then slowly runs down. So it appears that the fuel pressure is not the problem.

I took a video of the motor starting and the fuel pressure gauge as it start and dies and holds the pressure would it be helpfull to post a link to a youtube link?
or is that done on this forum?
Cheers and happy 4th from Canada!

[rougeaut]

Figured it Out, Motor Running Just Fine

Hey just an update to let you know that this new motor to me is now running!
The trouble shooting process went through, commpresion testing, spark to plugs, correct wiring of coils to cylinders, complete fuel pressure testing and injector cleaning and replacement of one injector, fly wheel removed and checked for stripped woodriff key, timing was checked and reset.
I recently went through my SELOC manual and reviewed all of the sensors and how to test them. Even though the motor was starting and quickly stalling the timing was right on and when the Throttle Position Sensor(TPS) was tested it was not working so I replaced the TPS and now it fires right up and sounds great and runs smooth(although I have not put it in the water yet) as I am just finishing off a new floor installation so very soon. The total time that was spent on the motor was about 8-10 hrs and many beers thinking about the process but all in all having a Yamaha diagnostic software and connector could have saved some time but would not have helped me out with the clogged fuel injector. Anyway another Yamaha motor mystery figured out.

Thanks for your insight and or advice I believe it is good to have a sounding board to bounce off ideas and I hope to be able to help others I have helped many in the past and will try to continue to do so.

I went out and bought a gift card for a local beer and wine store for the mechanic at the Yamaha dealership that not only offered me advice but was willing to give me a complete VST tank and high pressure pump to take home to test on my motor for free.

PS a friend of mine once rebuilt a 250hp 2 strk motor completly and had the same problem as he started out with loss of power on WOT, took it to a few shops spent the money but no one could figure it out and after all of that he was sitting at the dock with the motor running without the cowling on and he was smoking a cig and noticed as he reved the motor up and it was losing power that the cig smoke was being sucked into the intake for the carbs but when being reved up one carb did not draw in the smoke. I turned out that the butterfly valve was loose/stripped on the shaft and when opened up to higher RPM the butterfly valve was closing starving the air to the cylinder, so you just never know.

Cheers and tight Lines!