I picked up an 04 YFZ the other day with the following performance mods:
TC racing exhaust (Supertrapp) with spark arrestor removed
Ron Wood intake with K&N (basically just an open intake with an Outerwear)
Cam mod to advance to YZF timing

I put the spark arrestor in the muffler in an attempt to quiet it down a bit. But now it is running a bit rich. The Supertrapp has rings you can put in the tip for more flow and the ones on the front have fresh carbon on them after yesterdays ride.

I would also like to go back to the stock airbox, probably with or without lid depending on the conditions. Any suggestions for a base jetting?

 

Allen, if you go back to the stock airbox you could try a 172 main and maybe a 45 pilot. You could probably stand to add a few discs to your pipe, that would lean it out a bit. A bit of carbon build up is going to happen, I wouldn't worry to much about that.

 

That is one good thing about switching to this machine, someone is always going to know the answers. [img]i/expressions/face-icon-small-smile.gif[/img]

I was taking discs out to quiet it down. But it is still loud either way so I will add some back. Hopefully the airbox will quiet things down. If not I suspect that a Q series pipe will be in order.

Is there a PDF download of the service manual or a site with pictures of how to access the jets? I am strictly an amatuer at this. There is a site that had every instruction for the V-force.

 

I didn't think it was that loud? Jet access isn't that bad. Loosen the clamps on either side of the carb, remove the breather hose that sticks up from the engine to the left of the carb as you are sitting on it. Also on that side near the top of the carb is a black plastic peice held on with 2 torx screws. Undo those screws and gently wiggle the plastic peice off. That is part of the TPS, and it can be easy to break the wires if you don't remove it prior to rotating the carb. Now you can rotate the carb, bottom towards the left, top AWAY from the TPS side fo the carb. This will get you access to a plastic plug(I think it is 17mm) on the bottom of the float bowl. Remove this plug and you have the main and pilot jets right there. The main will be a hex/socket style body, the pilot has a slot for a screwdriver. They are right next to each other. Actually, if you follow a line from those to the engine side of the carb, the fuel screw is recessed up there, outside the float bowl. Access to the needle is on the top of the carb, remove the top, and it is above the slide, held in with a set screw. There are a few YFZ specific sites out there, and most have a tutorial somewhere. I also like the HMF site, lots of good jetting info there. Thumper talk is great as well, as the FCR carb on the YFZ has been a popular oem offering for the mx bikes as well.

 

It's 165 main and 45 pilot. But they've got the NVCQ needle in there on the 5th clip. I'm going to try moving it back and see how that does.

 

Wow, 165 on the main seems like it would be lean with your setup, but the quad seemed to run OK? Have you put the stock airbox back on yet?

 

I haven't checked it myself but I emailed them and they said it was a 165. It seemed OK. I guess having the YZF needle and it being that far out makes up for the difference in jetting?

I am going to get the airbox back on soon, I need a few screws and an airfilter.

 

If you are buying a new filter, go with a Uni or Twin Air. The K&N stock replacement has a better mounting system than stock, but I don't trust them with the fine dust we see in the summertime.