OS 1.40 Dies at Throttle Up

[ronlock]

Hi  all,

I have an OS 1.40 with only 15  flights on it.  Break in  and first 15  flights
over last couple of months were fine.   

Yesterday first two flights were fine. Carried plane to take off position for
third flight, engine went rich and died at throttle up.   Re-started and
got same result.   Changed to new OS-F plug, and went to lighter
load prop.   Same result.  Set high  speed needle to near peak.
Same result.   Been using same jug of 15% nitro fuel for all flights.
Pipe is Bolly 26 inches piston face to baffel- same as first 15 flights.
Ive checked fuel lines, tank, remote needle, carb,  for leaks, and for
flow -  all seems OK.    

I discovered I  can blow air thru the pump in  the direction of fuel flow,  
but not backwards.    Anyone  know, is that normal?

Other suggestions?  -  What changed between 15th and attempt at
16th flight?

Thanks,   Ron Lockhart
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