1990 300ce 24valve . lpg conversion

I have a 1990 300ce 24v. which runs on lpg as well as petrol (gas). When I slow down fairly rapidly whilst running on lpg after having driven at speed the engine sometimes cuts out at about 20mph. I have removed the scoop on the air intake and this has slightly improved the situation. Any other ideas or experiences with this conversion. Apart from this problem the system is great and allows me to avoid expensive U.K. petrol prices.