1980 Honda cb650 keeps dying! Why?

[Sponny]

Here's the skinny:

1980 Honda cb650 Custom keeps dying on the road. It initially starts out fine, but after traveling in 3rd or 4th gear for a while, I notice that it's not responding as much when I open the throttle. Then, when I try to take it up hills, it completely peters out, like I'm not giving it any gas at all, and it just shuts down. Each time I get it started, it gets harder and harder to start until it won't even push-start. When it comes to an idle at a stop, even if I keep revving it, it'll shut off. It died on me like this about a month ago and I took it to a Ducati shop to be serviced (there are no Honda shops in my area). They said it was the carbs and completely cleaned them, timed, and serviced them. They even put a little fuel filter on the main fuel line. But I just test-drove it again today, and after about 10 minutes of riding, it happened again and I had to push it home. I thought it might be the battery, but I just checked it with a voltmeter, and it's fine. Other things I have done to this bike: replaced air filter, fuel tank, petcock, fuel line, tires, battery, adjusted and bled brakes, and had the carbs professionally cleaned. It's still not working! Help! Why does my bike keep breaking down like this??

[guardrailjim]

Bad coil.
When they heat up, the internal windings expand and separate.
When the coil cools down, the wires contract and reattach themselves.
Keep a known working spark plug with you.
When the engine dies, immediately check for spark.
Pull off a spark plug cap - insert the good spark plug - lay the threads of the plug against the engine and try to start the bike.
Check all 4 spark plug caps.
If a spark plug won't spark, get the coils checked.
And check the spark units (common problem with Hondas of that era).