Yep. Bad coil or bad condenser. Both will often work fine when cold, but then fail when warm. (not warm from under-hood temperature, warm from operating under electrical load) I don't know how to tell which is the culprit since both give the same weak-spark symptom.My 1935 ford is difficult to start after I have run it for about 10 miles. If I let it sit until the engine cools down it starts immediately. I suspect that I have a bad coil but would welcome any comments or advice that anyone can give me. Thanks for your help.