I have installed a Ryobi in the 86" span Sparrow Hawk and it moves along at scale speed and will loop with ease, but when I dive to pick up speed it goes off song.
I seems to want to stay at the same speed and I thought it was going rich so I put the vent to the carb through the fire wall but it made no difference.
I now think it just cant get enough fuel like the carb is too small.
The motor has the slots in the bore, bowman ring,rex ignition, 150 timing, but standard carb.
Any ideas what could be going wrong as it would be a great setup if I could solve this problem.
Also this is the 3rd ryobi I have and it seems to have more clearance on the big end and has a clicking sound when hand starting, is this normal with some Ryobi's

If they are a little rich on the high speed and run fine in level flight - when you dive, they will four stroke

You might try a little more pitch on your prop.

If you dive and the engine ceases to be pulling - it will tend to four stroke

Wbye
You could be right as the prop would unload in the dive and so would the load on the motor.
I have a 18 x 8 on it but I have a 18 x 10 that I could try.
I get 7200 from the stock carby should I try a bigger one or stick with the smaller one.

7200 with a 18 X 8 and the stock carby is doing pretty good for a Ryobi.

That is sort of the sweet spot for torque for a Ryobi. I don't think you should go to a 18 X 10 unless you cut the diameter down to 17"

There are so many variables involved here, You may try a 11.11mm carb? This would be a Walbro #28 in a Ryobi. The stock carb is a Walbro #20 (7.94mm)