Good deal Spion, didn't think you typed like you were from around here!
You might want to leave that 140 in there for a week or so, it will wash out the gear box before you put the 90 in. You might also want to consider synthetic!
To increase speed, tighten the 10 mm nut on the governor arm, (on top of the tranny), speed will increase the more you turn it in. Or search "speed spring", (available from our venders).
And welcome to the site!!
On edit; that 60/140 might be ok with your climate. Just the 140 seems alittle thick for your area. Hope others chime in!