Installing a Pro 1 tachometer

I don't expect you to know exactly what what your bf did with his ride, but a carb needs to be more than just 'flushed' if problems are suspected. It needs to be carefully cleaned and inspected, and set to factory specs that it may have fallen out of over the years.

Assuming that he's a wizard and did all that appropriately, might I suggest checking the ignition coils per the factory workshop manual?

You might have gotten the coil and plug wires too wet.

Either give it a day or two to dry out, or spray them with a thin coating of WD-40, wipe dry, and try starting.

SOURCE:installing a Pro 1 tachometer
look on stadium yamaha website you will see where they are

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r u getin fuel-is the tank valve workin-maybe the float is stuck on carb-test to see if getin spark-ignition system could hav bad wire ie plug or coil connect