Fat Boy 4 Complete Exhaust Systems-Yamaha YFZ 450

INSTALLATION DUNCAN RACING
INSTRUCTIONS INTERNATIONAL,INC


FAT BOY 4 COMPLETE EXHAUST SYSTEM

MODEL: 2004-06 Yamaha YFZ 450


1.Remove stock exhaust system; Retain stock head nut and allen bolt. (’06 model has 2 head nuts) It is also necessary to remove the nut from the lower right side sub-frame mounting bolt. (bolt does not need to removed) Mounting tab on tail pipe will attach onto this bolt.

2.Before starting your Fat Boy 4 installation. You must make sure that the cylinder head exhaust gasket is intact and in good condition (usually they stay in the cylinder head). Under normal conditions it is OK to reuse them. If they are missing or in need of replacement they may be purchased from your Yamaha Dealer Part # 3VD-14613-01-00. DO NOT RUN MACHINE WITHOUT EXHAUST GASKETS. It also a good idea to make sure that the (1) exhaust stud(s) mounted in cylinder head is in good shape. If there is any doubt of it’s condition. Replace.
Improperly sealing exhaust gaskets will decrease performance and can also cause engine to pop and back fire, especially when engine is decelerating.

3.Install Fat Boy 4 header pipe using. Use stock oem head nut(s) and bolt. Hand tighten only.

4.You are now ready to install the Fat Boy 4 muffler/tail section. The tail section is secured to the Fat Boy 4 muffler at the factory before shipping. If these (4) 6mm stainless button head allen screws are ever loosened or removed they must be reinstalled with some form of medium strength thread lock (recommended Loctite 242 Blue).
Before sliding tail section onto header it is recommended to apply a thin coat of hi-temp silicone to the inside of the tail section (female side) approximately covering about ½” of the initial part of the tail pipe. This will keep exhaust from leaking at the slip-fit joint and make removing pipe in future easier.

5.Install the (2) 8x25mm flange type bolts (supplied by DRI) in the muffler mounts going into sub-frame. Make sure mount on tail pipe is slide onto right hand sub frame bolt and re-install nut. Tighten muffler bolts and sub frame nut securely.

6.Tighten header pipe. Make sure to tighten header bolt/nut evenly.

7.AIR INDUCTION: For maximum performance DRI recommends installing a Pro Flow Air Cleaner kit (billet flange, K&N Filter, Outerwear) with air box lid removed.

8.Carburetor jetting must be changed see below for additional recommendations

9.Additional Performance and Jetting Recommendations;

For the best performance using your NEW Fat Boy 4 it is recommended to use a Pro Flow Air Cleaner Flange system with either a K&N or Uni air filter. The kits are made by Pro Design and are sold through Duncan Racing. The K&N filter makes the best power and it is recommended to run air box with the lid removed.

Jetting Recommendations:
The following guidelines are for YFZ 450’s with the following type set-ups.

Sea Level Temperature between 60° and 90°

Fat Boy 4 Complete Exhaust System Stock Engine
Pro Flow Air Cleaner Kit (with K&N) Air Box Lid Removed.

Carburetor Settings:
Pilot #45
Needle Stock #5 (down from top) (’04-’05 Needle is a NDSR)
Main Jet: #180
*The 2006 model needle (# NGNR) has a non-adjustable needle clip. In most cases the stock needle is adequate. But if any symptoms of a lean condition occur it is recommended to install the ’05 YFZ 450 needle (Yamaha part # 5TG-14916-V1-00)
This needle maybe purchased from DRI or a Yamaha dealer.

*DRI has included at no charge the necessary jets for the above jetting changes with an extra main jet each way.

The above specs should be an excellent starting point for most installations.
Jetting should be checked after install.

Be careful not to run machine to lean-engine damage may result from a lean condition.
To rich power will be lost, engine will run flat or blubber.

Jetting Notes:

Colder temperature requires richer settings.
Higher elevations cause engine to be low on compression and generally require leaner settings.
Air box lid on requires leaner settings than with lid off.

For more information contact:

Duncan Racing International, Inc.
10734 Kenney Street Suite A
Santee, CA 92071
USA
(619) 258-6306

Check our Website for additional YFZ 450 Performance items.

www.duncanracing.com