Have a chinese ATV 4 stroke 90cc motor. I am replacing stock plug with iridium ngk plug. what gap should i use?

also does the gap need to be changed if i go to a high performance coil and if i go to the high performance "blue" cdi?

 

.024 to .030 will work on the performance parts.
Making sure you have good air flow and up to a 22mm carb with 93 octane fuel will also help with more power. It is hard to find performance pipes and exhausts at any reasonable price. I would take a long, thick screwdriver and rod out the baffles in the muffler to open the exhaust up some. It will help. Most of these mufflers are a 3 part baffle with some packing for sound. If you can line up the interior baffles to allow more exhaust to escape out the back of the muffler directly you will decrease restrictive back pressure.

HTH, Rich

 

thanks Rich.
I havent purchased the high performance parts yet just the plug. Thats an interesting approach on the muffler. when you say "rod out the baffles" do you mean just jam the screwdriver in through the hole in the muffler and punch holes basically? the end of the muffler has a chrome piece but its riveted on.

 

Not really, more of using a long, large screwdriver to align the baffles, not break them.
If you can look into the rear of the muffler you will see that the holes are offset to add back pressure. If you can bend the cheap steel to open that alignment up you will have more flow through, better sound, and less back pressure.