Runs on gas tucks over rough on petrol when switch to no fuel it runs really well

I have a 3.5 v8 gas conversion engine runs fine on gas when I switch dash switch to petrol it runs rough but when I cut fuel supply to switch to gas it runs spot on. Changed fuel filter and has new plugs. Any one had this problem?

My guess is the carbs are flooding when you turn the petrol of the carbs stop flooding and it runs fine until they run out of petrol.

Mick

texpis said:

My guess is the carbs are flooding when you turn the petrol of the carbs stop flooding and it runs fine until they run out of petrol.

Mick

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+1

Check shut off valves in carbs, they dry out and stick

tomkettlewell said:

I have a 3.5 v8 gas conversion engine runs fine on gas when I switch dash switch to petrol it runs rough but when I cut fuel supply to switch to gas it runs spot on. Changed fuel filter and has new plugs. Any one had this problem?

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I have this with mine. I start it on petrol when cold, and then move the switch to the off position, this turns the fuel pump off. After a few seconds, the carbs run dry and I can then move the switch to the gas position and the engine runs fine. If I try to switch to gas before the carbs are empty, then it runs really rough.