Help needed

[Anhquan1]

hi guys,

im new here and new to boating. I just bought a used boat with a 2008 Yamaha F90tlr on it, motor start right up and stay idle but if I try to trim up or down engine will kill and can't start again, engine alarm goes off after each time I tried to start. If I try to start it after 15-20mins it will start right up and if I try to trim it will kill again.
The guy I bought the motor from told me that the engine was running good with no issues, only thing he recommended was changing the lower unit oil since he didn't have a chance to get it done.
these are things that I did to the motor after purchase:
-oil change
-new spark plugs
-fuel filter
-lower unit oil change
​​​​​​-adding a water separate between the fuel tank and engine
-adding a different type of kill switch
can you guys give me any suggestions where and what to look for? Any help are greatly appreciate.

****the fuel bulb will get firm after few pumps but as soon as I stop it will soft again.

 

[ClassicAQ]

You've got 3 principle outboard systems...fuel, compression, and spark, the latter including electrics. Considering the engine kills only when operating trim switch, this isn't a compression or fuel issue. Therefore your focus should be on spark, specifically the electrical system.

Check cranking battery volts (12.75)
Volt drop test T/T wiring, ignition harness wiring, including the ignition kill switch wiring

 

[Anhquan1]

You've got 3 principle outboard systems...fuel, compression, and spark, the latter including electrics. Considering the engine kills only when operating trim switch, this isn't a compression or fuel issue. Therefore your focus should be on spark, specifically the electrical system.

Check cranking battery volts (12.75)
Volt drop test T/T wiring, ignition harness wiring, including the ignition kill switch wiring

Thank you, I'll give it a try.