Yamaha 90F won't start

[Wcatman]

2003 F90TLR 4-stroke - can't start. Battery full, new fuel pump and spark plugs, Eth.free gas, bulb pumped hard, Turns over strong but just won't fire. Any suggestions what it might be appreciated?

 

[rejesterd]

So the engine cranks well but doesn't start.


It's likely one of the following:


1. No spark is actually being produced. Changing the spark plugs was a fine thing to do, but you have to actually confirm that each wire is producing spark. Get a spark plug wire tester from any auto parts store.. very cheap and useful. If the wires are producing a strong spark and you recently replaced the plugs, assume everything is good there. If no spark is being produced, start working backwards from the spark plug wire, to the coils, to the main wire harness on the engine, to the starter switch, to the starter relay, and all the way to the engine stop lanyard. Eventually you'll find the problem part by testing for continuity at each of these places.


2. Not enough fuel is being delivered. When you turn the key to the ON position (without trying to crank it), can you hear the electric fuel pump whir for a few seconds? If not, check the fuse for it. If the electrical pump seems fine, check the fuel pressure. If the pressure is way off, start looking at the injectors. If the pressure is fine, check the vapor separator and the pressure regulator. If those are fine, check the fuel rail for leaks. If that's fine, check the fuel filter and fuel lines for clogs. Then move onto the mechanical fuel pump and the vapor separator needle.


This is all straight out of the service manual, which you should definitely buy if you don't have it. Well worth the $90 or whatever it is. It will tell you exactly how to test all this stuff and what order to do it in.