eliclem

Hi i have a merc 314 sprinter, i know this is a ford forum, but i thought id try anyway.
my lpg /petrol van runs ok on petrol , but when i change over to lpg it starts going into limp mode it doesn't cut out but can only be driven at 20 mph.
In a morning it will start fine ,if i drive home the night before on petrol for the last few miles. If i forget and come home on lpg it misfires until i get on a long run at speed.
If I set off on a journey and start on petrol , I may have to pull over several times and switch the engine off before I can finally switch over to gas and it run properly.eg start journey at Penrith and finally switch to gas at Morecombe.
I am desparate if anyone can help Id be really grateful
yours ELICLEM.