I have a normal cam, the one, that is in the engine when you buy it.
Lumpy cam meaning large lift and/or duration. If yours is the factory cam, you're good with standard ignition and carb. You asked if changing the cam will help power or gas mileage. I hate to use this phrase, but it's the only one that fits: It depends...

Gazillions of cam profiles are designed for different reasons. However, there are two main categories...gas mileage or performance. You generally don't have the luxury of both...although some offer an acceptable balance. If you didn't go crazy with a wild cam, then you can assume you should have decent mileage. The only way to really tell is to determine the best cam profile for your driving needs. You can contact any cam mfg and tell them you need a cam for ???? reason. They will ask you a bunch of questions like street or race driving, type of induction, headers, gear ratio, vehicle weight, etc... They can pretty much hit dead on with what you need.

The question about what's a weak spark is subjective. If you pull a plug and crank the engine to watch the spark, you should see a "powerfull" blue spark (maybe about an 1/8 inch wide). If you see a little "tick" (maybe a small line less than 1/16 inch), then you've got a weak spark. Yip, I know, subjective huh?

Hope this helps...

tj