Toyota Carina E - Toyota Carina E autogas (backfiring) - Gregory II

I have a Carina E which has an autogas installation. It is hunting when driving and backfires through the exhaust every so often. What are the most likely causes of this problem. The installation is a Lovato installation.

Thanks for any feedback.

Regards

Gregory

Toyota Carina E - Toyota Carina E autogas (backfiring) - Gregory II

Can anyone tell me if a fault in the shut off valve as per the picture below. I removed a part from it but I believe I placed it the wrong way round. I can't remove this part now and I think I will need to replace the whole valve.

http://q2autogaz.pl/zawor-gazowy-lpg-lovato-p-51.html

Also can someone advice where I might be able to obtain a manual for servicing LPG installations. Further to this, what precautions should be taken when changing this shut-off valve with a live gas system?

Thanks