[AZKen]

You have a fuel delivery problem NOT vapor lock. Could be several things. Tank not vented (gas cap old and not functioning). You got a bad fuel pump right out of the box. I just have a feeling you are focused on "hot day, wait til it cools" when it's really gradually losing fuel and/or fuel pressure and then "opening up again". As in : vent problem, fuel pump diaphragm not pumping enough or losing pressure/suction, clogging somewhere and then unclogging. Drive with gas cap loose, check the carb squirt, do a fuel pump flow test, replace filter (where is your filter?), check carb screws. If you can start it with fluid/gas...it is fuel delivery. Maybe that's obvious and you know that already but I have to say it anyway. Pulling out choke to run is a give-a-way. Been in the family thru many summers? I guess it's possible you re-routed some hose or fuel line recently near exhaust manifold or added something under the hood that blocks air flow now. Hope it's not a load of bad gas. Has it been sitting? How long? Everything from tank cap to pickup tube to all the way to intake manifold must be checked. Every inch of the delivery system. Test and troubleshoot, you will find it. Vapor lock is rare now a days, albeit Ethanol has a lower boiling point. You CAN NOT have E10 stored in your tank for more than 30 days without burning thru the motor.