I have an 1986 Merc 150 XR2. It had some firing issues that I thought was the switch boxes so I replaced them. If I take out the plugs and check each to see if firing they are now, however if put them back in and try to start it nothing. It simply spins but ever fires. I have tried starting fluid in the carbs & in the cylinders and still nothing. I have left all the plugs in and check to see if I get spark from plug wires and I do on all six cylinders, but again if hook the wires back to the pluggs a try to start all it does is spin. I have checked the fuel pump and it seems strong. I dscounnected the fuel line going into the bottom carb and it pumps plenty of fuel. Need Help!!!

u need to see if all the cylinders are getting fire