Hi KrisB
I have the same problem with my JES9800A. It's 6 years old, and has been that way since day 1. The 6" burners are excellent. The dual 5/9" burners are extremely hot on "lo", and can incernerate the gates of Hell on "Hi". When I sear steaks, I do it on lo, and turn the knob on lo for 2 minutes, and turn it off for 1 minute. French toast is 1 minute on, 1 minute off. Makes cooking a joy, I tell you.
I e-mailed Jenn-Air to see if there is a fix for this. No response. So I called them, and was told that this is absolutely not normal, and they scheduled a technician to come out. 2 days later, they responded to my e-mail, saying they apologized for the inconvenience of burning all my food, but they had looked in the litterature for this model, and it's operating perfectly - no need for service. If Jenn-Air intentionally designs ranges to operate this way, they might be in the wrong business. Maybe someone should cook on it before they market it?
I had the tech come out anyway, in case he had some tricks up his sleeve. He said the parts list said to replace the original switch with a new part number, though he couldn't guarantee that the extreme heat was the reason for the new part number. Because my alternative option is to rip the whole range out, I'm having him go ahead and replace the switches in a couple of days. I'll let you know if it helps. I've looked at the new switch, and it seems to have an adjustment screw that adjusts the distance between the bimetal switch, which would certainly allow for some temp control adjustment. We'll see, we'll see. Please let me know if you come across any other way to fix yours. | 
