Can covalently bonded hydrocarbons be influenced by a magnetic field? I am doing a University project on Magnetically Assisted Combustion and am curious to know more about how magnetic fields may or may not affect gases such as butane and propane. 

I think I am right in saying that due to the gas molecules being covalently bonded, there are no free electrons to be influenced in anyway by an induced magnetic field.

Someone briefly mentioned something about that depending on whether they are saturated or unsaturated but the conversation didn't go any further as he then promptly left.. so I am still unsure.

If anyone could shed any light on this or has any thoughts at all I'd be very grateful for your input.

The method of some experiments I have done was attach a neodynium magnetic arrangement around the fuel line of a gas burner and measuring heat transfer to water.  So far the results have been fairly inconclusive as I am using a camping stove which has problems sustaining a constant gas flow as well as a number of inconsistonsies with heat loss and human error etc .. but that's another issue.
Just because there are no unpaired electrons doesn't mean magnetic fields can't influence something. Unpaired electrons tend to lead to strong interactions with magnetic fields (the dioxygen in air has two and is paramagnetic, an effect best seen in the liquid phase where a magnet will attract the cold liquid).

But compounds with paired electrons also interact with magnetic fields, though the effects are usually weak. But the repulsive effect is sometimes strong enough to levitate a diamagnetic substance (see this youtube video showing how strong magnets can levitate plates of graphite which is strongly paramagnetic).

It is unlikely that such effects would be easy to see in gases. But you are talking about combustion and the most likely effect will not be on the neutral gas but on the flame where the gas is not neutral but a plasma of charged particles. Charged particles or molecules will have a much stronger interaction with a magnetic field though it might still require sensitive apparatus to detect how the field makes a difference.