My buddy just bought a new YFZ450. He was thinking that if he ran with the airbox lid off, stock pipe and K&N filter, he might gain a few HP. If he was to run this set-up, would he need to re-jet? I heard a stock YFZ runs slighlty lean from the factory, so with this increase of airflow..would he need to re-jet? We are at 1000 feet above sea level..

 

I was just running mine w/o airlid and baffle on stock jetting all weekend, but that was at the dunes at 5000' elevation. One of the guys I talked to there said on his, also stock with baffle out and lid off, he went to a 165 main jet and his home elevation is 3600. Stock main is something like 150 I think. I'd say at your elevation you should jet up, although the 4 strokes are more forgiving than a 2 stroke in this regard.

 

Anyone else??

Bump

 

go up to a 168 main and a 45 pilot then buy the air/fuel mixture screw and then you will be able to fine tune it. this is running with no airbox and haveing the baffle removed.. p.s. if you buy a K@N filter make sure you get and outerwear for it or your engine will be toast after all the debris get through it.

 

What do you mean..buy an air/fuel mixture screw? A YFZ doesn't have one?

 

the screw is at the bottom of the carb in front of big bolt that incloses the main and pilot jet. its a hole with a screw up in it.