Well from the factory they come with an NGK DR7EA plug. I changed mine to an NGK Iridium IV DR7EIX plug because I had a few ebay bucks that were gonna expire and didn't know what to spend it on lol. I think after the change, the throttle response is just a tiny bit better.
Well if you don't mind spending 10 bucks on a spark plug i would go with the NGK Iridium. You'll never have to replace the plug, ever. Can't really tell you if it starts any better, my 250 has always been real good about starting up quickly. On a cold start, its like less than a second after i hit the button that its started and running. And when its warm out, I don't even need to choke it to get it cold started. But if you're having trouble starting your quad, I would adjust the valves, that should fix your problem.
your still breaking it in? I'm sure you got way more than the recommended 20 hours of no more than 3/4 throttle riding time on there.. Once you go through about 3 full tanks of gas you can start riding it full throttle, you don't really need to go by what the book says, almost nobody does lol.
Jeez, I think your dad needs a little engine knowledge.. You should show him the periodic maintenance chart in the service manual that came with the quad, and show him that a valve adjustment is necessary. don't you have any friends that are good with motors that could adjust your valves for you?
Yeah, that is the factory NGK plug that comes in the 250. haha, i bought 3 of them on ebay and it cost me about 20 bucks too lol. Then I bought the iridium plug, and i still have 2 brand new factory plugs in the NGK boxes lol.