Sounds like more of a choke issue if it runs well after start up, then runs poorly after warm. Does it run poorly at idle or at speed. Have you made sure your idle mixture is correct? What kind of fuel pump are you using? It could also be timing related, running to far advanced. There are a lot of other things to look at that can cause the problems you're having.

Using a wood/phenolic resin spacer helps, but I think you would be throwing money to the wind. Sounds like you have a problem that can be solved without spending money first.