If you have a new glow plug, I would try that. I use the OS A5 and they work a lot better on the NT-16 than the stock glow plug. Since switching, I also noticed I do not have to leave the glow igniter on the plug as long. I can pull it off as soon as the motor starts. With the CEN plugs I had to let it warm up a bit before pulling the glow igniter off. Not sure that's your problem, but it's worth a try.