The oven does not heat well. I can tell the bottom element (or burners) ignite, but nothing is heating at the top when the bake cycle is started.

I have already changed out the igniter, just in case that was not operating fully; even though the broiler worked (and still works) fine.

After I changed out the igniter, there is still no upper flame, but there is a strong gas smell. Is there anything I can do to fix this myself or do I need to call a service person?