I was wondering if you need to rejet after installing a new exhaust? I have a yfz450 and was thinking of getting the Dr. D slip-on Exhaust but don't know if it's necessary to rejet?

 

if it flows more yes.

 

Definitely yes. YFZ450s run a little on the lean side stock anyways, and anything more than a K&N Air Filter is going to require a rejet to give the carb more gas.

You'll like the slip-on exhausts though. It really wakes up the YFZs.

 

What size jets would you recommend?? I know there are alot of different configurations but is there like a "standard" config size for jets??? I've read the the rejet "kits" are a waste of money??

Also I was looking at the K&N filters and I saw a "Pro Design Pro Flow filter kit" that includes the K&N filter, pre-filter, billet base plate for $140. Is it worth it or should I just buy everything seperate??

 

Not sure what year your yfz is (though the engines havent changed much at all)but I have an 08 just installed a pro flow k&n. The stock filter did a pretty good job, k&n will allow it to breath a little better. I have been using their filters in my cars and trucks for years. Jet kits are a waste of money, if you know what size jet you need. Stock jet is a 158 (main). I have talked with several techs and mechanics about jetting for specific pipes. The advice I have gotten is that the stock fuel mixture needle is just fine, and stock pilot jet will also work with most aftermarket exhausts. this eliminates 2/3 of the need for a jet kit. most recommend around a 170 main jet. though it could vary from 165 to 175, depending on elavation. I think the only increments that are typically found above 160 are 165, 170, 175 etc. Individual jets run about 3-5 dollars each, much cheaper than kit. if you decide to upgrade needle and pilot at a later point you will still spend less for them individually than in a kit.

 

yeah I have an '07 450. I guess maybe I should contact the mfg of the exhaust and see what jets they recommend with it.

So the "Pro flow filter kit" would be a good buy then or just the filter itself???

Thanks for your help

 

The manufacturer of the exhaust is usually pretty good with providing you the correct jets for your application, but you'll still want to do a spark plug check afterwards to make sure you aren't too lean.

Jetting is similar for all pipes, but it can differ greatly depending on where you live in the United States (elevation), and if you opt to run without an airbox lid or not.

I went with the Modquad Billet Air Intake kit, which is going to be very similar to the one you're thinking of getting, and very similar to Yamaha's own GYT-R Air Intake kit.



I went a step further and purchased another air box lid off of Ebay, cut out all the plastic leaving just the rim edge, and then I threw an oiled "Filterskin" around it. That way, I could essentially run with the airbox lid off, and still prevent most of the dust from even entering the air box to begin with (dramatically decreases how many times you need to clean and reoil that K&N!). I got that idea from a fellow forum member here, and it works great! I really got sick of cleaning the airbox as well as cleaning the stock foam filter every other ride before I went with this setup.

 

Thanks Klier, you've given me some great info. I'll look into the modquad kit as well.

Do you have a link to that lid mod?? looks interesting.

 

Whether you go with the modquad billet kit, the GYT-R or whatever, they are all pretty much the same. You'll pay a lot more for the GYT-R engraving on the Yamaha one.

I don't have any link to the specific airbox lid mod that I did. But what I did is get an airbox lid off of Ebay. Example: Airbox lid Note: Don't get anything from this particular Ebay Customer... they suck.

Then cut all the inside plastic out with a dremel or other cutting tool, just leaving the 1 cm of rim around the outside. This is your "frame" for the filterskin.

PC Racing makes the filterskins that I get. I think Dennis Kirk had them in stock. Let me know if you're thinking about going down this route and i'll get out my paperwork on the specific size you're going to need. They are basically white nylons that slip around the frame that you made. Then just oil them up and you're good to go.

Like I said before, I can't take credit for this invention. A local guy that happens to be on the list showed me out at Tri-County late last year, and it seemed like a great idea. He was also spot on with the jetting I needed for my '07 YFZ and my HMF Pipe.

Good luck!

 

I just compares all 3 and yes the GYTR is way over prices just like your typical "dealer" parts...haha

I think I like the Mod Quad filter kit the best so I'm gonna order one.

I found the PC Racing website and filterskins. They have one for the yfz450 for around $15. Is that the one you got? I also found THIS ONE but they want $80 for the kit but then again it does use an Outerwears filter which is water resistant and doesn't need to be oiled, just washed from time to time. I think I'll try your way first on the lid MOD.