Hi!
Have you checked your tank position?!
Center of tank should be inline with center of fuel intake orifice in carb when airplane sits horizontal. Simple as that!
It could also be a leak somewhere in your tank set up , in conjunction with too large tank and long fuel lines and vibration leading to fuel foaming in tank.
Wrong glowplug, fuel and so on...everything is depending on everything else!
This is what I would do...
Fuel: 5-10% nitro, No more is needed.
20% castor oil or synthetic oil or a mix....in Europe 15% all synthetic oil like Motul "Micro" from France.
Glowplug Enya 3 or OS 8, these are two of the best sport glowplugs available.
Tank: 8-10oz tank...not more! The best tank however is the Tettra "Bubble-less" fuel tank from
Dave Shadel (Y&S US importer).
Tank should be close to the firewall with as short fuellines as possible.
I would recommend using a two clunk set up (a Uni-flow set up) , one line going to pressure nipple on silencer and one to carb, You also have a third line for fuel overflow, totall 3 fuel lines.
This is a more reliable tank system than an ordinary tank set-up.
Fueltank must be protected in soft foam...not placed directly onto wood surfaces in fuselage (like on most ARF airplanes).
Propeller: 11x6 for general sport flying. APC is one of the best.

Regards!
Jan K
Sweden