running hot what should i do

[Crusty450er]

well here is the story. i broke both of my legs so right now i am letting my older brother run my quad. all the engine mods i did to it it still ran fine with the stock jetting. never overheated and the engine fan never kicked on. i thought my fan had something wrong but my local honda shop checked it out and said it worked fine. i have a hotrod +3mm stroker crank with a 12:1 piston back in it from the original 14:1 piston. a full leo vince exhaust on it , and a R and D power bowl and my quad ran fine with the stock jetting. my brother and a couple other people said i needed to open up the air box lid and let it breath. i dont want to run without the lid cuz i ride in the woods and seen on a couple of my buddies that had those airbox outer wear lids leak water in them so i agreed to let my brother put a couple holes in the lid and insert those Uni air vents with the foam in it. he put three holes in the lid. ran it for about ten minutes and said throttle response was perfect. sitting at idle my fan came on and was starting to over heat. ran it again the fan stoped but when he stopped and let it idle after two minutes the fan came again. so whats going on is it running too lean making it run hot and need a bigger main jet? i dont need to ruin my new topend. any info would deeply appreciated. thanks

[d3ktrix]

Any increase in air flow no the intake will require richer jetting.

And with all the engine mods u have done, especially the head porting, the air box lid is really holding back air flow that those mods could be using to make much better power.
Did you ever think about an HRC air box lid?

No is really going to be able to recommend a start point for your jetting unless you either remove the airbox lid or get an HRC lid.