Venusaur

[BurningMan]

If you don't run sunny day on a pokemon never use solar beam, yeah the power is nice if you are up against weatherless team, but if your opponent switches in an opposing weather starter you will be trapped to fire of a 60 BP solar beam wich both tyranitar and politoed can tank (or they just switch to a resist) and you will lose a lot of momentum.
I don't know what the EV spread was designed for, but i guess it is designed to get some key KOs with EQ and or HP Ice (likely against Heatran/DNite/Jirachi) so i wouldn't change it unless you feel you absolutly need more power.
Now that Giga Drain is legal with Chlorophyll i don't think there is much reason to use Solar Beam because Giga Drains recovery reallly pairs well with Venausaurs natural bulk making it much harder for your opponent to revenge kill you.

 

[alexwolf]

If you don't run sunny day on a pokemon never use solar beam, yeah the power is nice if you are up against weatherless team, but if your opponent switches in an opposing weather starter you will be trapped to fire of a 60 BP solar beam wich both tyranitar and politoed can tank (or they just switch to a resist) and you will lose a lot of momentum.
I don't know what the EV spread was designed for, but i guess it is designed to get some key KOs with EQ and or HP Ice (likely against Heatran/DNite/Jirachi) so i wouldn't change it unless you feel you absolutly need more power.
Now that Giga Drain is legal with Chlorophyll i don't think there is much reason to use Solar Beam because Giga Drains recovery reallly pairs well with Venausaurs natural bulk making it much harder for your opponent to revenge kill you.

It is viable to run Solarbeam if your team is built to trap and kill other weather inducers. You just won't be able to use your Grass move 'till late game, which doesn't really matter, as Venusaur is supposed to be a late game sweeper, especially with Growth and Life Orb.