Hi Guys,
I just joined this site today and read all the previous posts on this topic.I am electronic eng. by profession. Actually a TAP is not dependent on if the engine is EFI or Carburated. Rather if the car is point type ignition or ECU (electronic engine control) type. I have a Charade 84 (contact point type) and i was facing the same problem a few months back. ultimatly
I designed one for myself and installed in my car. The performance, both power and economy wise, has improved a lot. My milage on highway is around Re. 1/Km.
Regarding the power loss, other than timing, its has to do with the fact that
CNG,unlike petrol, occupies some physical volume therefore reducing the intake airflow to about 15-20% and reducing the volumetric efficieny of the engine by the same amount. There is no remedy to this problem except in turbocharged vehicals. I checked the horsepower of my car on a dynometer and it was about 20% less than petrol after i installed my TAP whereas it was 40% less without TAP when timing is set for petrol.
The TAP doesnt mechenically advance the distributer rather electronically delay the ingnition signal depending upon RPM.
In the end my question for bilalahsan. The timing values given by you, are they only for TAP or they are total advance including the mechanical and vaccum from your distributer. Cos i am confused here as in either case it should never be less than 10' and also should not fall off in the end rather become constant after about mid RPM (3000 or so).
BTW contact point type TAPs are not available anywhere in Pakistan (as far as i know). You guys will either have to import them or make one like me.
Hope i had been informative.
Thanks
Zia