Keihin 39mm FCR-MX Install, DR650

Oh boy, I stay away from TT for most of the summer and come back and what do I see?

Rob started another looooonnnngggg carb thread. :crazy:

The sad thing is this one sounds as good as the 1st.

Rob ole buddy, you got to much time on your hand. Did the wife leave you? :D

HA HA keep up the good work!!

Rob,

If I were to order it from Sudco, which carb? Just 39FCR MX?

Assuming this carb only comes in a side draft configuration?

My V-max has four 39 FCR downdrafts.

Thanks,

Gary

Sudco's FCR-MX carb are different than the OEM YFZ450. The OEM YFZ450 carb is around $620 from Yamaha. Then the mod cost! :crazy: Sudco's price ain't much better at around $575 and then you'd still have to figure out the push cable. They say they have a bolt on air horn that will fit the DR650 but they've never put the MX model on the bike before. I figured out it would fit with help from Sudco providing me detailed dimensions. Sudco has only put the regular street bike FCR's on the DR650. They have a link to my web site now so they can show that the MX will fit but I don't know the bolt on air horn's configuration. Those prices are what started me looking at used OEM FCR-MX's.....

okay looks like buying a used one is the the ticket.. I've scoured ebay and not having much luck.. Anyone have a source for these used?

If not, I'll just continue to search until I find one and hopefully you'll still be doing the mod.

Worse case, let's say I had to break down and order one new, which year YFZ450 should I choose?

Thanks,

Gary

I've been getting the one from the 04/05 YFZ450. I hear they are all the same... even the later models but I have no way to confirm that. Certainly they would have the blank push cable casting no matter what year. The only other thing that could change that might screw us up (but I doubt it) is the basic intake spigot and air horn diameter. Since they use the same casting for 37, 39 and 41mm carbs it's highly unlikely they'd change that. :crazy:

Hi Rob - Great job. Got a question for ya. I picked up an FCR37 a few months ago (real cheap like on ebay) thinking I could make it work on my KLX300. I called the KLX guru in California and he said what I had was an OEM FCR (TPS, built in hot start plunger, etc, power now mod) and as such it's unable to be made to work on the KLX. Is there any hope on the DR? Is the 37 too small anyway to increase performance over the BST? Do you have any pics of the unmodified FCR so I can compare?

Thanks in advance

Dean

Hi Rob - Great job. Got a question for ya. I picked up an FCR37 a few months ago (real cheap like on ebay) thinking I could make it work on my KLX300. I called the KLX guru in California and he said what I had was an OEM FCR (TPS, built in hot start plunger, etc, power now mod) and as such it's unable to be made to work on the KLX. Is there any hope on the DR? Is the 37 too small anyway to increase performance over the BST? Do you have any pics of the unmodified FCR so I can compare?

Thanks in advance

Dean

The 37, 39 and 41mm FCR-MX's all share the same casting. I don't know about the regular FCR's. As far as making it work on your KLX... it would only be an electrical issue.... in other words, if your KLX uses a tps or other input device from the stock carb to the ignition system. Other than that, and having the space for it, there is no reason it couldn't be made to work that I can think of.

Yes, 37mm would not be good for the DR I'm affraid. Down low would be great but mid to top would suffer I think. :D

I haven't taken any pics of the unmodified carb. I'll see if I can do that and post it for you tomorrow. :crazy:

mx_rob, re: your comment that you think the 650 would suffer mid to top with a 37mm carb. By no means am I argue ing but I am curious. I've started to investigate the feasability of putting a 38mm TM Mikuni on the DR. The 38 gives up 10% crossectional area to the 40. It wins some back because it has no butterfly. My reasoning is that I never rev past 80 or 85 % of max revs so I would have better velocity in my rev range and better metering. The 37mm has 86% crossectional area of the 40. Again, it wins back some because no butterfly. I could see starving the top of the top end but I'm not so sure about the midrange. My understanding of these matters is rudimentary but it sorta makes sense to me. My BMW R100GS Canadian model has a 40mm CV per 500cc jug. The US model has a 34mm CV per jug. Thats a huge difference. Transmission and final drive gearing are the same. b

mx_rob, re: your comment that you think the 650 would suffer mid to top with a 37mm carb. By no means am I argue ing but I am curious. I've started to investigate the feasability of putting a 38mm TM Mikuni on the DR. The 38 gives up 10% crossectional area to the 40. It wins some back because it has no butterfly. My reasoning is that I never rev past 80 or 85 % of max revs so I would have better velocity in my rev range and better metering. The 37mm has 86% crossectional area of the 40. Again, it wins back some because no butterfly. I could see starving the top of the top end but I'm not so sure about the midrange. My understanding of these matters is rudimentary but it sorta makes sense to me. My BMW R100GS Canadian model has a 40mm CV per 500cc jug. The US model has a 34mm CV per jug. Thats a huge difference. Transmission and final drive gearing are the same. b

I'm no volume expert... I just know that volume does not increase in a linear way as diameter increases... it's more exponential. It certainly would be worth a try with the tm38 flat slide. I put a pair of them on my Norton "Battle of the twins" road racer back in the late eighties. It's not a fourstroke design carb though so you will end up with some difficulties in getting the low speed overlap working right. I did a ton of jetting and throttle valve swapping to get the 850 Norton running right. It went like a bat out of... well you know, in the end though. :crazy:

mx_rob, I'm no volume expert either and I work in forced air heating and air conditioning (sheetmetal mechanic), what does that tell you. I know it's not a straight line on the graph. OK more research. Maybe I'll have to whip out the ductalator. I guess whats leading me astray is that I can think of numerous examples of the same engine with different carb sizes in the interest of moving the powerband around. Anyway, thanks for your input. b

OK My final carb from eBay arrived today. When I walked in the door after work my kitchen reaked of gasoline! :applause: My son had brought the box into the house like normal. This idiot seller shipped me the carb full of gas! He had it wrapped in about 5 or 6 priority mail bags for his packing material and then put it in a box. My wife wanted to know if I had ordered a box full of gasoline....:crazy: What a dip stick this guy was. I wonder how he kept a straight face when the post office asked him "is there any perishable, flamable, exsplosive or liquid items in the box?" He lied through his teeth on 3 of the 4 when he said no. :D

I'd love to try it too, but I'm not sure how my older designed engine would respond.:crazy:

I'd love to try it too, but I'm not sure how my older designed engine would respond.:D

If you have a 95 or earlier DR650 the FCR-MX will not fit. The starter motors are mounted higher on the older design engines. The 96-2008 engines just have enough clearance. You might want to look into a regular FCR. They are big time shorter because of the smaller non baffled float bowl. As far as your engines response goes... it would be something like "Oh H*ll Yeah" if the carb you have on it now is a CV. :crazy:

If you have a 95 or earlier DR650 the FCR-MX will not fit. The starter motors are mounted higher on the older design engines.

On the REALLY early models with no E-Start you can use the FCR. Max Kool mentioned that a buddy of his had one on a stroked engine and that it was very responsive and great to ride.

On the REALLY early models with no E-Start you can use the FCR. Max Kool mentioned that a buddy of his had one on a stroked engine and that it was very responsive and great to ride.

Ah yes, I hadn't thought about the non-electric start DR's... yes, a properly sized FCR or FCR-MX is good for any engine that you could fit it on. :crazy:

okay put me on the list then.. if I don't win the one on ebay tomorrow I'm sure I'll have time to get another one after looking at that long list of names.

Yes I am!!! :D. My GSXR can is on the way, I'm just hoping I won't be testing them out in the snow.

Make sure you post any jetting changes that the GSXR can requires if necessary! The more info the more cr*p to read..... no, wait a minute... the more info the better. Yeah, that's the ticket. :crazy:

In re-reading the ride impressions from both Rob and Motoretro, I can't wait to get one of these carbs! Only thing is, I'm going to need a new aftermarket pipe too because I want that ripping mid and high end to go with that big thumpy torque!

i cant wait to read the ride reports. :crazy:

but at least I got to open it and see it, touch it, caress it... ok a little to far you guys get my point.

LOL I get the point...that is one sexy looking piece of equipment. To me the FCR is to the BST as thongs are to granny panties. Take that verbal SAT :crazy:

And if anyone want's to send their FCR this direction for your winter, I promise to look after it and test it thoroughly and send it back properly broken in...

Maybe...

Man if the FCR is doing this well on the DR I bet the KTM guys could get major gain. I think we always knew the BST was a piece of CRA%&%.

Ok Rob your wife is still putting up with you. I know you couldn't be spending much time with her unless.....................................did you get fired? :crazy:

Just kidding ole boy, good job on the FRC project. But man did you ever waste time on that old BST project. :D

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