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HOW TO: DR-Z400 FCR 39MX Carb Install

How to upgrade the DRZ400 Stock Mikuni BSR36 Carb to the Keihin FCR39 MX Carb.

Much has been written about the OEM DRZ400 Mikuni BSR36 carb, you can jet it, tune it, tweak it, but in the end, it’s still a CV carb with limited potential and lacklustre performance.  Check here to see if your DRZ400 has the CV Carb.  You have probably decide the extra HP and better throttle response of a well jetted FCR39 carb was worth the price.  What follows is installing the FCR39 on to your DRZ400 which is not hard. Though some general knowledge of motorcycles and Carbs specifically is important anyone with decent mechanical ability and basic tools can perform this install.

First, you need to acquire a Keihin FCR39 MX  or FCR39 carb. You can find these on eBay but be careful – there are several worn out carbs on eBay from other makes/models of bikes that can potentially cause you a headache down the road. ThumperTalk.com has a  Keihin FCR39 MX kit that fits all DRZ’s having a BSR36 carb, All S and SM models, and 2007 and later E model bikes. This is probably your best bet.  Below is a description of what they include.

The ThumperTalk kit includes:
– 016-925 Keihin 39mm FCR MX Carb with choke (no TPS)
– 021-216 FCR Adapter 2 3/8″, carb to S airboot
– 021-439 Adaptor O-Ring
– 017-262 EMN Needle
– 021-012 Airboot adapter bolts (2)
– P/N 13111-29F00 OEM Suzuki E Intake Manifold
– P/N 09402-58208 OEM Suzuki Clamp
– P/N 13685-29F00 OEM Suzuki Vacuum Port Nipple

Carb comes standard with the following:
– 200 Main Air Jet
– 160 Main Jet
– 45 Pilot Jet
– 100 Pliot Air Jet
– EMR Needle

Prepping the new Carb and bike for install

Remove and discard the plastic throttle wheel guard, it will interfere with fitment relevant to the frame, and really is not needed.

Move both upper motor mounts to the left side; this allows needed clearance for the throttle wheel
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The TPS connector will not be reused with the new FCR carb, you can follow the carb end up wiring to the connector and unplug it there. Use some dielectric silicone and tape to blank off the connector, you can cut the wires there, heat shrink or tape the ends, or simple stuff the carb end of the TPS and wiring harness up under the seat, zip tie it in place and leave it. Bottom line, it is not used for this install.

Remove pilot air jet  it is not used for this application

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If using a vacuum operated fuel petcock like the OEM one found on the DRZ S or SM, you will need to install a vacuum nipple in the manifold. Luckily there is a spot just for this and an OEM part to install. It is P/N 13685-29F00 OEM Suzuki Vacuum Port Nipple and included in the TT Kit.

Intake adapter too short? (see bottom of page for FAQ).
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DRZ400 Basic Jetting (FCR39 MX Carb)

Install the jetting required for your motor modification level and riding area. Below are four of the most common jetting setups. For many, that’s all they will need to do, for some, additional tuning will be required. Use what is here for a base. 

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DRZ400 FCR39MX Jetting for: sea level, stock exhaust or quiet 96db aftermarket pipe, 3×3 Mod 

  • 155 main jet
  • 200 main air jet
  • EMN needle
  • clip 3
  • 45 pilot jet
  • remove pilot air jet
  • 2 turns fuel screw
  • o-ring mod

  

DRZ400 FCR39MX Jetting for: sea level,aftermarket pipe with open muffler

  • 160 main jet
  • 200 main air jet
  • EMN needle
  • clip 3
  • 45 pilot jet
  • remove pilot air jet
  • 2 turns fuel screw
  • o-ring mod

 

DRZ400 FCR39MX Jetting for: 4000-600ft, stock exhaust or quiet 96db aftermarket pipe, 3×3 Mod 

  • 145 main jet
  • 200 main air jet
  • EMP needle
  • clip 3
  • 45 pilot jet
  • remove pilot air jet
  • 2 turns fuel screw
  • o-ring mod

DRZ400 FCR39MX Jetting for: 4000-6000ft,aftermarket pipe with open muffler

  • 150 main jet
  • 200 main air jet
  • EMP needle
  • clip 3
  • 45 pilot jet
  • remove pilot air jet
  • 2 turns fuel screw
  • o-ring mod

  

The Fuel needle clip position is counted from the top, flat end of the needle. The needle pictured is in clip 3 position.
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Install tips

No need to buy new throttle cables, the stock S cables work fine. Attach the throttle cables with the curved one on the bottom.
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Hoses are routed like this
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DRZ400 Jetting Accessories

In addition to the above or custom jetting, an extended adjustable fuel screw is highly recommended.
Merge Racing makes a very nice one. 

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Be very careful on the removal and install of the new fuel screw.. you have a small spring, washer and rubber O-ring that sits on the screw inside the body. One or more of these part sometimes remains in the body, and comes out haphazardly on the end of the old fuel screw. Very easy to lose one or more parts.

Installation FAQ

Q: The intake adapter appears to be too short. What now?  

A: The intake adapter really is not too short. People say this all the time due to the physical measurement between old carb set up and FCRMX being different, the FCR setup is slightly shorter. The air boot is plenty long enough. The preferred technique is to put the carb in the boot first. Then pull it forward to the manifold. If you are working in a cold environment, take a hair dryer to the boot and try heating it up slightly until it become plyable. 

Credit and Resources:

A big thank you and credit to E.Marquez and Bronco78 at ThumperTalk.com for this information. You can read the original article here: https://www.thumpertalk.com/forum/archive/index.php/t-649485.html . They are a great resource for the DRZ400. Also for rebuild information visit: https://www.dirtrider.com/tech/141_0707_keihin_fcr_carb_rebuild/index.html

Related posts:

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7 Responses

05.17.10

Great site. A lot of useful information here. I’m sending it to some friends!

05.17.10

nice post. thanks.

05.17.10

seen a good deal on a 37mm fcr carb from a wrf 250 which is also used on the 450.. will this work on my drz ?

05.17.10

I would not go that route. It would not be an improvement over the Mikuni BSR26 and would be a pain in the butt trying to jet it. I also can’t verify that the air box or intake connections will fit.

05.17.10

Just got my Keihin FCR 39mm
For my 09′ SM. Love it but I used my own
Boots that I sized up from Home Depot
For cheap. Call me what you want but I
Rode all weekend with no gas or vacuum
Leaks. I also did not have to move motor
Mounts only because I wAs scepticle.
Rock n Roll! Bwaap bwaap

05.17.10

Great article.
Just trying to muscle mine in.
The petcock hits the carb.
Any ideas?

05.17.10

It’ll fit, just work it in!

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