Does it do this all the time?
When tank is full.1/2 full,empty?-If mostly after a 5 minute run Check your clunk.
Is this a new conversion?If it is use another glow plug.When breaking in an engine the first one will go bad.
Retune maybe.Could be a little rich?
The pump membrame could be going bad as some carbs cant take the nitro.You only need 10 percent nitro.I thnk av8tor has had problems with zama especially.Check on the gas/glow threads.Just the newest one will work.