The reactivity of C(P-3(J)) atoms towards methylacetylene and allene has been investigated using complementary experimental methods. Kinetic measurements performed over the range T= 15-295 It have yielded thermal rate coefficients: (2.7 +/- 0.6) x 10(-10)(T/298 K)(-(0.11+/-0.07)) and (3.5 +/- 0.8) x 10(-10)(T/298 K)(-(0.01+/-0.12)) cm(3) molecule(-1) s(-1), respectively. Crossed beam experiments conducted in the range of relative translational energies epsilon (tr) = 4.9-282 meV have yielded integral cross-sections for H(S-2(1/2)) production that are proportional to (E-tr)(-0.56+/-0.02) and (epsilon (tr))(-0.55+/-0.01) respectively, in excellent agreement with the temperature dependencies of the rate coefficients.