Opening them allows for air to be coming threw when you need it to, and when your not riding in deep snow. And closing them would be for if you are riding in deep powder. That way it cant get inside your hood, because it will either create snow piles in areas where its not warm enough to melt the snow, or it will melt and when you let your snowmobile sit it will freeze again and make a possible mess such as if it melts in the air filter then freezes. Or gets in your airbox and then into your carbs/engine. But chances are when you're riding in powder is when you'll be working the engine the most so you will want air flow. You be the judge on whether to keep them open or closed depending on the conditions.
You should be able to install those vents with out any problems.I always leave my vents open.When your in deep powder they will plug up with snow any way.I have seen the vents your talking about on sleds it looks like it would give more air to cool.
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