ok....
i know this.. to start engine need only 3 things.
1) Air: check your air filter, Carb opening, idle screw
2)Fire: glow plug, get the hot one or the medium one(yer LRP no.4 is it hot or cold?)
3)Fuel: good fuel(old usually it will not start) & fuel flow. restricted or not.

Im using 25% nitro & the 28 built for 30%. need to remove shims to 0.3mm or 0.4mm.

check this 3. if these ok... open your engine. have a look inside.something not right.
for me... always my glow starter . i borrowed from firneds..it start rightfully.