i have a camaro 97 with lt4 heads 200cc i just install an msd ignition 6425al but when i drove the car starts to stumble and when I unplug the msd the car is just fine i think that could be the spark plugs what spark plugs did you recommend? or what could be the problem ?

 

Sounds like the MSD is the problem. More often than not they are horribly misused and people blindly install them onto their cars thinking they are an upgrade when in many cases they are a step backwards. I would remove it altogether - the stock ignition system is more than capable for 95% of cars out there.