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</head><body><p>Hello, everyone. <br></p><p><br></p><p>Question: I'm trying to fix a motor that starts and runs fine for 20 minutes (timed it), then falters and stalls. I've bypassed the fuel system, rebuilt the carbs, replaced the carbs, and had the distributor rebuilt. Replaced spark plugs, wires and points. Even swapped out to an electronic ignition. In short, it's neither electrical nor fuel. <br></p><p><br></p><p>The good until full operating temperature is what I'm left with. Could that mean a cracked head or bad head gasket? (Don't think it's valves because it runs fine until it heats up.) <br></p><p><br></p><p>Thoughts? And apologies for crashing the list.<br></p><p><br></p><p>Terry Smith, '59 TR3A<br></p><p>New Hampshire<br></p></body></html>