Fuel Problem: Vapor Lock?

[chopper]

Difficult to say without knowing what type of carb, cam, distributor, ignition, etc you're running. However, just off the top, I would be surprised if the coolant temperature you're seeing (205 degrees F) would be enough to cause vapor lock. It sounds like you feel it's a fuel starvation problem. If it is, when the car stumbles, check to see if your accelerator pump can squirt some gas into the carb. If not, the bowls are empty and I'd go from there. I'd probably be more apt to look at the fuel pump to see if it's running a little weak after it runs for a while and heats up. If there is fuel in the float bowls, the problem is more likely ignition related. You may then want to check your ignition system to see if the spark is getting weak as a result of overheating of the ignition box or similar problem. Where is your ignition system located? If it's under the hood, it may be overheating. I have mine (MSD) mounted under the dashboard on the passenger side, to keep it out of the hot underhood environment. What type of distributor are you running? I originally had a Mallory Unilite optical pickup distributor, and had random problems similar to what you describe. The Unilite optical modules can't take the vibration and heat of the engine and I got random problems. I eventually trashed it and went to an MSD billet. Just a couple of ideas. This type of problem is difficult to track down. I wish you luck.