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FCR MX Jetting for XR650L. Where to get started?

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After some deliberation on sourcing a replacement to the stock cv carb, I picked up a FCRMX carb.

http://www.thumpertalk.com/forum/showthread.php?t=703866&highlight=fcr+mx

The carb is from a 2004 Honda CRF450R, and includes the throttle and cable. The carb size should be 40mm. As far as I can tell, the carb is stock, straight from the bike, and includes a hot start and throttle position sensor.

I have a few questions and I couldn't find any threads with jetting starting recos for the fcrmx (there's a few for slant fcrs) so....

1. Any tips for getting started on the rejetting? I'm at sea level, bike has 1mm overbore high compression piston, hot cam, modified airbox, and high performance stickers.

2. I know the throttle position sensor is useless with the xr. Do I remove it?

3. Hot start. What about this? Plug it somehow?

4. Stock XR choke cable. I'm assuming this is now useless. Remove?

Thanks.

-Scott

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After some deliberation on sourcing a replacement to the stock cv carb, I picked up a FCRMX carb.

http://www.thumpertalk.com/forum/showthread.php?t=703866&highlight=fcr+mx

The carb is from a 2004 Honda CRF450R, and includes the throttle and cable. The carb size should be 40mm. As far as I can tell, the carb is stock, straight from the bike, and includes a hot start and throttle position sensor.

I have a few questions and I couldn't find any threads with jetting starting recos for the fcrmx (there's a few for slant fcrs) so....

1. Any tips for getting started on the rejetting? I'm at sea level, bike has 1mm overbore high compression piston, hot cam, modified airbox, and high performance stickers.

2. I know the throttle position sensor is useless with the xr. Do I remove it?

3. Hot start. What about this? Plug it somehow?

4. Stock XR choke cable. I'm assuming this is now useless. Remove?

Thanks.

-Scott

I know mines a non mx FCR, but I found the jetting to be almost identical as it was with my CV.

The enrichener cable is now useless.

The TPS I'd leave in if there is any chance of dirt getting in with it gone.

Not sure what to tell you on the hot start.

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Sudco makes an awesome manual for that carb that details all of the tuning tips and tricks...It is directly from Mikuni....I don't have any experience with any of the other questions, but I do have the book and it is great to get you all jetted correctly.

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Sudco makes an awesome manual for that carb that details all of the tuning tips and tricks...It is directly from Mikuni....I don't have any experience with any of the other questions, but I do have the book and it is great to get you all jetted correctly.

That might be for a TM. The FCR is a Keihin.

Do you have that book in PDF form?

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I got this info from Eddie Sisneros TT's resident jetting expert when setting mine up.

ok,this should be pretty close.

165 main jet

200 main air jet

dtp

clip 3

45 pilot jet

100 pilot air jet

2 turns fuel screw

The hot start valve on mine is a push/pull knob and I left it as is, the enrichner is the same right above the hot start and was left as is. I wound up with a 178 main. I used an FCRMX from a KTM.

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The FCR MX is a Keihin carb and not Mikuni.

I thought about calling Sudco for advice, but remembered that when I called them a while back, they mentioned that unless you order their FCR MX carb setup, they will NOT provide jetting advice.

-Scott

Sudco makes an awesome manual for that carb that details all of the tuning tips and tricks...It is directly from Mikuni....I don't have any experience with any of the other questions, but I do have the book and it is great to get you all jetted correctly.

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sounds good, where did you pick up the carb ebay? wonder how much of the stock jetting in that carb will stay the same, did you get any stock info for whats in that carb yet? Curious how the cables will work if there long enough, and where you can notice difference over stocker. Sweet deal, your bike should run awesome with your upgrades

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Denn,

Yes, from ebay. I found plenty offered as buy in now and priced ridiculously high. If you're patient, wait for the true auctions and one can pick up in the $200 range.

I have yet to mount the carb as I'm wrapping up the crf fork swap first, so I can't comment on performance. My carb came with the stock throttle and cable, so I'm assuming those will mount without issue. One note, our bikes will require a carb to airbox adapter. I'm looking into that piece now.

I'm planning on calling sudco tomorrow to see if I can get some info out of them regarding jetting and add ons. More to come on this in the next week.

-Scott

sounds good, where did you pick up the carb ebay? wonder how much of the stock jetting in that carb will stay the same, did you get any stock info for whats in that carb yet? Curious how the cables will work if there long enough, and where you can notice difference over stocker. Sweet deal, your bike should run awesome with your upgrades

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Denn,

I have yet to mount the carb so I can't comment on performance. My carb came with the stock throttle and cable, so I'm assuming those will mount without issue. One note, our bikes will require a carb to airbox adapter. I'm looking into that piece now.

-Scott

Interesting.

Let us know how it fits and take a few pics. o fthe set up.

This is something I'd like to do on my 650L.

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first i've heard about this boot adapter as well... i was looking at the carb the other day thinking..... thats way small to fit on the stak airbox boot?!?

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Not only is there a diameter difference than stock carb, but since the carb is narrower, there is also a distance gap from carb to airbox. Apparently there is a company that makes the adapter.

http://www.nossmachine.com/honda_quad_parts.htm

It's labeled as TRX but should fit our bikes as well.

-Scott

first i've heard about this boot adapter as well... i was looking at the carb the other day thinking..... thats way small to fit on the stak airbox boot?!?

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yeah i found some in the $350 range and up for new but didnt really try to get too many, maybe someday but ill wait for now. what kind of valving and spring rates you gonna use with those forks??

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No the FCRMX is a full house carby - pumper the works

Holy ghost of Christmas past!

Good to know you still come on rmhrc.

Yeah, its a pumper, as is the non-mx FCR too.

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So a quick update:

Jetting: Ordered a few sized main and pilot jets from Jets R Us last night.

Carb to Airbox gap: rather than muck around with fabbing an adapter, I went ahead and ordered the pricey noss machine adapter. There's a lot of airflow forces at work, rather than risk causing turbulence and vis a vis poorer performance, it's best to suck it up and buy the part. A friend just got his yesterday and it mounted up perfectly.

Hot Start: The hot start cable wasn't included in my carb, so I have a gaping hole on the carb body. I could either purchase another plunger valve to fit in here and essentially "plug" the hole. Rather, I'm sourcing a hot start cable and will see if I can mount up to the stock choke assembly on the clutch lever.

-Scott

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so whats the price of this $$$$$ carb adapter????

you need to do a few pics too so we can add to FAQ section where parts need to be shown, like the air boot and hot start

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