LPG converters only provide LPG if they are told to by the amount of vaccum the engine has.
It is very typical for LPG motors to run out of LPG up high because the vaccum decreases as the REVS rise.
As the vaccum decreases so too does the signal to the converter for GAS flow.
So you may have either low vaccum or the converter might actually be too small. Either way , be careful as leaning out any motor under load can cause major detonation problems...............real bad
The LG Motorgas B2 will flow enough to suit 300+ horsepower if the motor is set up correctly to run on LPG only.
I'm currently running one of these in my Modified 351 and am getting to 5200 - 5500 RPM where it starts to lean out Big time.
The converter you have is WAYYYYYYYYYYYYYYYYYYYYYYYY to small
It is only rated to 100 HP or motors up to a max of 2.7 litres.
Check out their website : http://www.elko.com.au/page4.html
Sounds like you've just found a new paperweight for your desk!!!!!!!!!!!
Hope that helps somewhat