Abstract: A transient synchronization stability model incorporating current limiting and power coupling is established for virtual-admittance-based grid-forming inverters. Second-order quasi-steady-state relationships and numerical solutions of three state variables are combined to analyze instability mechanisms under voltage sags and positive and negative phase jumps. The analysis is validated through simulations and experiments. The results show that, under the investigated operating conditions, stability during voltage sags depends on both the separation between stable and unstable equilibrium points and power-angle dynamics, whereas stability under negative phase jumps is mainly governed by this separation. The system exhibits a strong self-recovery capability following positive phase jumps. The virtual impedance magnitude does not change the unstable equilibrium point under current limiting, while the resistance-to-reactance ratios of the virtual and grid impedances have opposite effects on the separation between equilibrium points. Reducing the virtual impedance magnitude and its resistance-to-reactance ratio improves transient synchronization stability and voltage support. The influence of power coupling on stability cannot be neglected.