Brand new engine. I turned the key, it started first pop!

Then, revved a little, and then started to misfire so I shut it down. Don't have anyone at home at the moment who can wiggle connections or check plug leads and don't want to leave it idling when it's brand new.

Does the same thing every time. Starts fine on four cylinders.

Then, when you give it some revs, it hesitates and starts to run on 3 cylinders.

There isn't any smell of unburnt fuel at the exhaust, and because it starts fine every time, I don't think it's flooding.

Suggestions welcome

Thanks