I have found that making sure that the fuel line has a gradual "up hill" slop to it all the way to the carb helps prevent vapor lock. I had a similar problem until I eliminated the "high" spots in my fuel line path. I still sometimes get vapor lock on really hot days.
You may also be experiencing cheap gas syndrome. I have found that cheap gas seem to vapor lock sooner the a national brand gas -- lower boiling point. You really are not saving anything by buying bargain gas.
These are my thoughts. I hope they help.
Walt L. Williams
La Verkin, UT
