@Zeejigs.... Cure's engine is not that weak my dear.. I can easily does around 130 - 140 on gas and can easily maintain its speed around 160 on petrol... It has one of the best small car engines...
@Rasheed: About your problem......
First of all make sure that Ur car pickup is at its max in the lower gears as well cuz if not then u need a proper tuning..
The reason ur engine is not giving its max response might be bad tuning...
Get ur engine tuned
Oil Changed
Clean air filter
And get ur CNG serviced by a good mechanic... There are a lot of chances that your car's gas mixture setting is upset...
IF all that does not work... then Check ur wheel aligments... this greatly affects the top speed..
If the tires are not properly aligned they may decrease a cars top speed from 150 to 110 easily... plus try to turn ur tyre while the car is on jack to see if they move easily... sometimes the internal Bearing gets stuck and the car becomes really hard to move.. .as a result the engine needs alot more power to move the car... check these small things and I am sure it'll be one of these faults.. If nothing works... tell me the condition of your car in detail .. .and I might be able to spot the problem....