I purchased the 3 piece Merlin plug set with the head clamp. The plugs have the red insulator on the top. I've tried to contact the owners at Merlin plugs over the past year several times. No one has responded to the questions I've asked. The site lists several plugs but only 3 of them in the Cox/Norvel category. The blue insulator is listed as a cold plug. I use 35% in the majority of my Cox engines. When doing so, I generally run approx 3 head gaskets to extend the life of the plugs. The most reliable plugs I've used as far as starting is concerned is the Cox 1702 high performance plug. This is what I use on the Cox Tee Dee. I can start the engine on 1-2 flips. The red Merlin plug wants to constantly run backwards and bump back at me on start up. I've had it even try to kick just bringing the prop up onto the compression stroke to begin flipping. This is telling me the fuel is pre igniting. It takes 4-6 head gaskets for me to get the Tee Dee to run with the Merlin plug. Would the blue insulator plug allow me to run fewer head gaskets and higher nitro without what I'm experiencing above? In general, I run the higher nitro fuels in my Cox engines and the lower nitro fuels in my Norvel engines. The Norvel engines aren't as fickle as the Cox engines when it comes to plugs or fuel in my experience. To save on fuel costs I've been trying to run my engines on 10%. This has somewhat worked out on the Norvel engines using Galbreath heads with hot Nelson plugs. These engines are being used for combat purposes so reliable starting and good performance is essential. The engine needs to be warmed up though prior to use in order for this to work. Otherwise I feel the head is cooling off causing the engine to die rich in the air. This becomes an even more of a problem using the Tee Dee. I would like to know from those using the Merlin plugs as to what color the insulator is and also what nitro fuels your using and head gasket information. Ken

          Hi Larry, I'm interested in the color of the top of the plug. My plugs are red and the Merlin site states this as being a hot plug. This would work in the AP as you probably have no need for 35% nitro. I wanted to use this setup on my tee dee and I find it too difficult to get a good needle using 10%. I'm using this for 1/2 A combat and not stunt. I almost have to hold the plane a bit prior to release. It takes me a few tries to get it set using 10% and this is certainly not good for combat. When I use the 35% I get quick reliable starts then I set the needle slightly on the rich side and launch. The Merlin plugs are a bargain compared to the Cox plugs and I would certainly like to get them to work. Ken

Ken,

If the element coil is sticking out into the combustion chamber, try gently pushing the element into the coil recess.  I had starting problems (pre-ignition) with my Merlin 1/2A plugs until I tried that.

I don't know why you've had problems contacting Merlin.  Try calling him if email doesn't work.  He's had some problems on-and-off with his PC so that could explain it.  I think he's in the UK right now, visiting family.  Try him in a week or so.

Fred