I purchased and installed a new K&N air filter yesterday on my 375. With the filter installed the machine hesitates (stumbles) at half throttle. If i choke it a little the hesitation improves a little but is still there. once it gets past the hesitation it runs great. Why is the filter causing this? What can i do to correct it besides putting the stock filter back on?

 

you have increased the amount of air coming into the engine. therefore it is running lean. you need to rejet your carb,if you dont know how to do this take it to a dealer.

 

Go one size bigger on your mainjet, and hang on