I have a 74 dt125 which starts and runs great for about an hour then dies.
If I wait an hour it fires back up and runs great for another hour or so then dies again.
When it dies, I check for spark (pull the spark plug cap, put a screw driver and hold it near the head, turn it over) and there is no spark.

Does anyone know, is this a Coil issue or something else?
 

If the battery charge is good when it dies, then most likely the ignition coil.  They can get pretty hot if someone leaves the key on with engine off and I've seen that burn up the coil.  You could check continuity right after it dies.

(I know asking about the battery sounds dumb but a few years ago someone had a similar problem and eventually it came out that he was connecting up a battery charger after it died...  which was something he didn't think to mention.  But that model needs a good battery to have spark)

Is it an electric start model? as we had both electric & magneto here. Only thinking magneto source coil if mag type, thats all.

I had the same problem with my 75. It ended up being the points. Replaced the points and problem went away

I've read that a dodgy condenser can lead to symptoms like these as well.