The pump may be a little too rich. Dial the pump Out CCW about 1/4 turn and see what happens.

What you are likely seeing is the richness is semi flooding the engine while its running. the DZ engines put raw fuel injected in the head...This will put the glow plug out.

Just because the plug looks OK or just because it glows doesn't mean its a good plug.

A glow plug is not like a spark plug....the plug coil is coated to provided the catalyst to aid in the combustion. This coating can burn off or get a hot spot in it...Plug coil will look OK but it will not be working properly in the combustion. Yes you can eye ball it and see if its bad, but in some cases it could have a slight flaw in it from a small hot spot in a critical spot on the coil. This will keep the plug from making the right heat and having the proper chemical reaction with the fuel.

In your case I think its just a little rich on the pump so lean it out CCW, and then reset your top end....Get the engine to operating temp slowly and then let it run at 1/2 power and see what is going on.

Usually the pump will have more to do with lower power settings as far as mixture in concerned....The HS will have an effect but its pretty minimal when the engine is below 1/2 power.

Troy Newman
Team YS