I have a 1985 GSXR 400 GK71B, difficult to start but when started runs for about .5 hr then stops. If I wait for about 10 mins it starts and will run for about 10 mins. Isn't fuel as I have fuel in the bowls. Replaced regulator and CDI. Tried freezing the pick-ups with a can of freeze but didnt seem to fix the problem. I get a spark when it wont start but very weak, spark when it is running looks ok. Runs well when it is running. Wiring looks ok. Any ideas?