Check the spark plugs. Incorrect, fouled, or worn spark plugs can make it difficult for the engine to start. If they haven’t been replaced recently, it might be a good idea to install new ones and see if that resolves the issue.

Another thing to consider is the fuel system. Water or air in the fuel system can cause starting problems. Check your water separator and fuel filter, and sample the fuel from the return manifold test port to make sure it’s clean and free of water. If you find any contamination, you might need to replace the fuel supply.