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School me on FCR39mx carbs

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1. I recently picked up a 11 DRZ400S and I may end up putting on a FCR39mx carb on my bike but before I even think about that I need to know a lot more about these carbs. This is my first 4 stroke dirt bike (been riding 2T sense the late 70's and have had a couple crotch rockets over the years) so I have a lot to learn on these new carbs. I need to learn all the tuning components and what effects what in these carbs. From the reading I have done I see there is a leak jet, Accelerator pump (AC), Main air jet, pilot/slow jet, needle, & main jet. Is there any thing I am missing??

2. Oh ya then there is the hot start thing which from what I have read I would not need on a Drz. But what is it and how does that thing work as  a couple of my boys buddy's have YZ400's (98 & 99) and I am sure I will be working on them some day probable sooner than later?? lol. I know all about TPS from my sleds so that is a non issue anyways and from what I have read I would not use it on the Drz anyways.

3. Then as far as the fitment goes to a DRZ??? I have read I need to use a few parts from the E model and a different air horn/ intake bell correct?? That brings up another question. So why cant I use a FCR off a YZ450. I have read its because it has a fixed intake bell?? If that's correct my next question being I am a retired Machinist with his own mill & lathe in my garage could I turn up the correct sized bell and just press it on to use the YZ450 carb??  I want to thank all of you who do reply in advance.

Edited by Zrt1200

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All the information you seek is in the DRZ400 section. So... I moved this there for you. You will also find if you use the search function for each of your questions, you will find 50 answers. The FCR39 for a DRZ has been going on over 16 years and a lot of experience is there.

Rip on!

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1 hour ago, William1 said:

All the information you seek is in the DRZ400 section. So... I moved this there for you. You will also find if you use the search function for each of your questions, you will find 50 answers. The FCR39 for a DRZ has been going on over 16 years and a lot of experience is there.

Rip on!

You were right. I just needed to type in the correct wording. lol. Here is why you dont want to use a Yamaha FCR...

 

Edited by Zrt1200

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You could also go the CVK40 option that is 80% cheaper for probably 85-90% of the power increase of the fcr , may be more , never seen a comparison, though . Would really be an interesting study to see just what differences a person could even feel between the 2 .

 

 

.

Edited by jjktmrider
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I think for a lot of people it comes down to cost. 

The reason I went with yfz carb is because it was dirt cheap (under 50 quid for mine) and you can still pick up 08 ones on eBay for under £150. 

How ever they do involve a lot of messing around not only to fit them but also jet them correctly. (I'm nearly there with the jetting note after a lot of trial and error)

If you have the money and just want to be able to fit a new carb with as much ease as possible I'd go for the TT kit. 

However if you're on a budget and have a machine shop, which if the case you probably like to make stuff any way I'd go with the cheapest know carb that fits the drz you can get hold of and set about modding it.

 

Other than hot starts and tps they are all mechanically pretty much the same as far as I know. 

Take a look at my yfz thread linked above it will give you a very good idea of what's needed to mod a carb to fit.

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In the second link on pg3 it shows a adapter you can buy on Ebay...

http://www.ebay.com/itm/Keihin-FCR-Carburetor-Adapter-for-DRZ-400-DRZ-400-APP-1001-2-Intl-Buyers-/172717593744?hash=item2836c55490:g:eKAAAOSwx6pYn7s1

I also found this adapter...

http://www.ebay.com/itm/182588836462?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Being I can buy adapters pretty cheap this makes buying a Yamaha or other brand FCR39mx carb a more reasonable option for someone who is on a budget. The sad part is you are always taking a gamble if you buy something off of ebay.

I also found this set up in my searching. Its a used carb that they sell with DRZ jets already installed....

http://www.keihin-fcr.com/index.php?route=product/product&product_id=55

From My searching it looks like these carbs will work. I copied and pasted these from the second link above. Read for your self though.

2000-2009 KTM 525 XC four wheeler
KTM RFS 4 stroke motorcycles 450 and 525
CRF450X
2003-2007 YZ450F
2004-2009    Yamaha YFZ450      39mm
2012-2013    Yamaha YZ250F      39mm
1998-2000    Yamaha WR400F    39mm
1998-2000    Yamaha YZ400F      39mm
2001-2002    Yamaha WR426F    39mm
2000-2002    Yamaha YZ426F      39mm
2003-2011    Yamaha WR450F    39mm
2003-2009    Yamaha YZ450F      39mm

 

jjktmrider. How is the throttle response on that CVK40?? Im not looking for more power but I am looking for a quicker throttle response. Who a I kidding I am always looking for more power. lol. Do you have a link to your CVK40 conversion??

Edited by Zrt1200

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I don't have the CVK40 in mine ,I bought a Harley Davidson version with an accel pump and was going to machine my own bell for the DRZ but haven't taken the time to mill one out(on my long list), Signman606 does, I believe. as well as a few others the normal carb without the accel pump . I have a FCR41 that was a refurb so decently priced and went that route , for now .

 

.

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I think power wise, both the CVB40 and FCR39 are about the same. The FCR is more responsive. You pay for that with a few mpg loss in fuel economy.

Most of the carb installs done with a non-removeable bell work decently, while some never run quite right.

The KeihinFCR site is very iffy. Sometimes guy have gotten good carbs, some have been royally screwed over. I would not rec. chancing it unless her sent you a carb first for you to test then then had you pay for it.

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Bringing this topic back up to update a little. I ended up buying a FCR39mx from a 2012 YZ250F.  I also found out you can do a little conversion on the airbox and use the Yamaha air box boot with a little trimming with a dremmel.

I did buy a carb adapter off of ebay to fit my FCR but may go with the air box mod. The only problem with that is its non reversible.

As you can see in the pics the Yamaha carb does not have a Main air jet in the bell of the carb. I am going to have to do some searching for jetting when using a Yamaha carb. I did measure the bore of the carb and I had the seller measure it as well before I bought it and it is a 39mm.

From the reading I have done I already know I will have to do a little filing to make the throttle cables fit correctly.

 

IMG_20170705_173641517_HDR.jpg

IMG_20170705_173702740_HDR.jpg

IMG_20170705_173713736_HDR.jpg

IMG_20170705_135053915.jpg

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To plug the hot starts on my fcrs I got the plug that Yamaha uses one the YFZ450 atv , #32 ,#33 , & #54 is needed . http://www.partzilla.com/parts/search/Yamaha/ATV/2007/YFZ450+-+YFZ450W/CARBURETOR/parts.html

 

#34 may be needed depending on carb and if it has the groove at the bottom for it , some seem to use it others don't .

If the seller left the plunger and spring in the carb all that is needed is #54 then .

 

.

Edited by jjktmrider

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Do FCR's flood if you crack the throttle when the bike is off?

 

And  they have the drip tube that will drip gas all over the place like my YZ did, right?

 

Looks cool but I would like to be able to bring the bike into my apartment which would definitely be a no go if im dripping gas in the elevator.

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Do FCR's flood if you crack the throttle when the bike is off?  

And  they have the drip tube that will drip gas all over the place like my YZ did, right?

 

Looks cool but I would like to be able to bring the bike into my apartment which would definitely be a no go if im dripping gas in the elevator.

 

 

Yes, each time the throttle is pulled it will shoot a stream of fuel into the intake like a squirt gun.

 

It is not really normal for fuel to drip from the overflow lines unless you tip the bike over. If it does it upright then you either have too high of float level or a leaking needle and seat.

 

You can always shut the fuel off at the petcock (assuming it's not stock) and run the fuel out of the bowl or carry a little allan wrench and drain it before bringing the bike inside.

 

 

 

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On 7/12/2017 at 1:15 PM, jjktmrider said:

To plug the hot starts on my fcrs I got the plug that Yamaha uses one the YFZ450 atv , #32 ,#33 , & #54 is needed . http://www.partzilla.com/parts/search/Yamaha/ATV/2007/YFZ450+-+YFZ450W/CARBURETOR/parts.html

 

#34 may be needed depending on carb and if it has the groove at the bottom for it , some seem to use it others don't .

If the seller left the plunger and spring in the carb all that is needed is #54 then .

 

.

Thanks for the link. My FCR came with the plug but I did not know it needed a O-ring under the Hotstart plug as mine does not have that. I will order one today. I just received some of my jets I needed and am waiting on main jets yet.

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Look down in the hole that the hot start plunger will go , if there is a ring groove at the bottom it needs the o-ring , if there isn't a groove then the o-ring isn't needed . Out of the 4 fcr's I've been playing with lately , only 1 had that groove . The carb vary in that area , I think it's the Yamaha oem versions mostly that need it but I'm not that familiar with it for sure.

 

 

.

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