RE: Merline glow plugs?
The OS #8 plug is sometimes too cold for a few of the Jett engines to run on. OS A3 or A5 are actually better. Usually the #8 will work in the sport jett engines, but if there is any hint of transition issues...... the plug is at fault.
Most of the Jett engines require a HOT glow plug. K&B1-L had been the baseline for quite a while. Rossi 2 and 3, McCoy56, others similar to that work well. On the 90LX engines we also recommend the OS-F plug.... the 4-c plug is very hot.
The Merlin Hot and Hot HD that Jett offers are well matched for the engines. In particular the post seals are some of the best in the business.