Hello I have a 04 Pred and it has a k&n air filter and a pure polaris pipe on it, and the guy I bought it from says he didn't rejet it. My concern is when I drive it, within the first 1-2 mins the fan comes on and I don't know if that's just how they are built or if its because of the pipe/k&n? If I need to reject it, what jets do I need if I also want to drill holes in air box for better performance. Any help and recemendations for anything to improve power is very helpful. Thank you

 

I'm no expert on this but I have been doing some reading on this. How does it run now? Does it idle good? Is the response good? Is WOT good? Any backfire?
Take the carb apart and see what main jet is in there.
A lot of folks say 5 over stock on the main jet is a good start for a pipe and filter.
I have a FMF pipe and aftermarket filter on my 03 and run a 155 main at just above sea level.
There's a lot of good reads on carb tuning and some good you tubes as well. The fuel/air screw, the needle clip and the main jet all need to be working together. Go slow, record where you started and make small adjustments to see if it helps. These carbs are very tunable but you need to know when and where to adjust.

 

it runs great, great top end, great idle, no backfire (unless I hit limiter). If it runs fine should i touch it? or should i just leave it as is. thanks a lot

 

Stock main jet should be a 150. Usually 10-15% over stock with a pipe and increased air flow,but it's just a rule of thumb. Some may run good,accelerate good with no bogging or hesitation with just the stock jetting or a simple one size jump on the main jet. Main thing is the color of the plug! If it's toward the whitish side the jetting needs to be bumped up. What you're looking for is a light to medium tan on the plug. Best way to check it is after a high speed run,kill it and check plug condition.

 

So after the high speed run take it out and check it while engine is still hot or once its cooled a little? Thanks a lot for your help i really appreciate it!

 

You can let it cool down,plus it's better on preventing plug thread damage/stripping on aluminum heads if you do,just don't crank it back up until you check the plug color.