I will check the bore of my 4oS , the 4o FSRS comes with two similar venturies of differant hole sizes .
More Nitro keeps the fires lit , if its a bit craky on that one , or a bigger prop will load it up more ,
I think I used a 10 x 4 three blade on my 40S in my 50 Oz Yak , and tried 10 x 6 & 11 x 5 .
If the Intakes the STOCK one it should be o.k .
If the Noblers under 45 Oz , the 35 or 30'd do the trick , and are lighter .
This Sucker used a Max 40 S ,
though if theres wind and youve got strong lines , go ahead . But theres NO POINT in adding tailweight , a shorter nose might be needed ,
and 43 Oz is a good weight for a NOBLER . a OS Max 30 S will fly one fine on 60s on a 10 x 6 or 10 x 5 .
The 40 S is here ,
http://sceptreflight.net/Model%20Engine%20Tests/Index.htmlsays 7.5 mm , 3.9 mm spraybar , 15.8 mm area . used 15.2 on my 25FSR . ! to fly 47 Oz Nobler Size .
Fitted a big max .20 one to choke down the Max 30 in a Gieske Nobler , 43 Oz , back in 76 .