Abstract: An internal combustion engine cold start device has an air valve which co-operates with a valve seat to vary the cross-sectional area of an gas supply passage upstream of a plug valve in the passage. The air valve is urged towards the valve seat by a coil spring and a plunger, which is urged towards a stop by another coil spring, provides a resilient abutment for the air valve which limits movement of the air valve away from its valve seat. The plunger is urged away from its stop, against the action of its coil spring, by manifold depression which is fed to the plunger bore by a short straight pipe.