Observed double-humped proton velocity distributions of the solar plasma are represented analytically by a superposition of modified bi-Maxwellians. Stability and growth rates of the cyclotron mode are calculated in linear Vlasov theory for a warm solar wind at 1 AU. Proton distribution function and cyclotron wave growth are discussed as functions of the beam to plasma particle density and the temperature anisotropy. The presence of a second ion component causes increased growth rates and a second resonant wave particle interaction.