Share taxis leave Phnom Penh from the Chbah Ampeau taxi park to head to Svay Rieng. The fare from Phnom Penh to Svay Rieng is 8,000riel. Grab an extra space for a bit more comfort (costs you more). Hour Lean Bus Company operates a daily direct connection from PP to Svay Rieng (cost $2, 3 hour ride). If you come from the Bavet border crossing with Vietnam it might be a little bit difficult to find a taxi, as most of them prefer the more lucrative option of taking foreigners all the way to Phnom Penh. Try to find a taxi with other travellers and to stuff yourself for a 1-hour trip into the taxi ($1-2).
Phnom Penh to Svay Rieng: This trip is a fairly easy lone for motorcycles, as you can easily skirt the potholes that slow down the cars. Keep those eyes open, though, as the share taxis that ply this stretch from Phnom Penh to the Vietnam border all seem to be trying for the Cambodian Land Highway Speed Award. They do fly and they don't let a little thing like a motorcycle hinder their flight.