With a gas engine, failure to run usually only happens when one of three things is missing:

1. spark
2. a suitable air/fuel mixture
3. compression

You seem to have tested and found a spark, I assume the engine has compression -- so all that's left is air/fuel.

Is there fuel actually getting to the chamber?

Choke it good, flick it over a dozen times or so, then take the plug out. If it's getting fuel, the plug should be wet (or at least have some trace of fuel on it). If it doesnt' then chances are that your fuel jet (or the fine mesh filter) in the carby is blocked.

I'm not sure what carby is used on the SPE but some of these engines have an incredibly fine (probably sintered) filter between the fuel pumping diaphram and the fuel-jets. If you have *any* dirt or suspended solids in your fuel, this filter will clog and the engine won't run.

The filter is usually a loose-press-fit into the hole and you have to push it back out using a rod from the other side. Once it's out you need to give it a blast with compressed air (against the fuel-flow direction) so as to get rid of all the dirt.

Is your plug damp/wet after choking?