OMG Keihin FCR33 racing carb

esspressolungo

esspressolungo

Senior Member
Joined
Jan 10, 2012
Bikes
Honda XR 250
I had the opportunity to buy a FCR 33 racing carb for my birthday, I didn't expect much, but this thing is "killer". It took me a while to get it fitted on my XR250L 1997, but after a few times to the machine shop my mechanic was able to fit it for me> The guy I bought it of assured me this carb was from a XR250R so the jetting should be pretty close.

When I went for the first test ride a big grin could be seen all over my face. When I installed a Sigma Kit a while ago I thought I had maxed out the power of my XR, how wrong was I.

The Keihin FCR 33 is a carb designed for racing and it sure delivers what you need when you race a bike. The lame XR250 has turned now into a semi-moto cross bike and the joy factor is beyond believe, so far I've been more then happy with the set-up, but will have to report back for fuel economic, so far I noticed a slight increase of fuel, I hope it will be in an acceptable range or it might as well be a tuning thing.

For now I just love the way my XR 250 responds....here are some pictures:

 20130713_105820_zps0628bbee.jpg
20130713_105811_zps90060902.jpg
 
Well done Rudi,looks like we will all have to be eating your dust next time we ride 555

I should add...theres a big difference between the OEM round slide and D slide (racing type) carb i changed to on my bike.
 
Loop said:
Well done Rudi,looks like we will all have to be eating your dust next time we ride 555

I should add...theres a big difference between the OEM round slide and D slide (racing type) carb i changed to on my bike.
Click to expand...

They're the best upgrade ever done to my bike, like this I don't need the XR 600 anymore, this is too much fun to be true
 
The accelerator pump will give that instant power when you twist the throttle, and a bit more fuel consumption. Are you running a stock exhaust or any exhaust mods planned ?
 
bill said:
The accelerator pump will give that instant power when you twist the throttle, and a bit more fuel consumption. Are you running a stock exhaust or any exhaust mods planned ?
Click to expand...
My mods are: 1. removed snorkel
2. grinded off the header welds
3.exhaust is a FMF Q4
As for camshaft I will stay with the stock setup, I had my valves hardened by a Thai guy. I had many XR's and this is so far the best set-up I ever had.I know I could do more, but I don't want to risk reliability over power, I am very happy right now, so why should I risk more.
 
esspressolungo said:
so why should I risk more.
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Why? Because there will be 3 x KTM 300's nipping at your heels. Can't have too much of a good thing Rudi!

But a great idea and I'm happy it's worked for you.

By the way Kiyosan is in town 1-21 Aug if you fancy a ride?
 
LUFC said:
Why? Because there will be 3 x KTM 300's nipping at your heels. Can't have too much of a good thing Rudi!

But a great idea and I'm happy it's worked for you.

By the way Kiyosan is in town 1-21 Aug if you fancy a ride?
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Yeah Darren, I know, I am under powered, because of my increasing weight, decreasing fitness and the fact that my mom's away next month and I have no one looking after my son, so I think riding will be impossible for me next month. By the way, did you switch back to KTM? I grew up with KTM, but at that time they were heavy monsters with lots of torque and impossible to maneuver, but that's a long time ago and now they lead the world with their bikes.

I think I gonna die with my XR, to long we've been good friends.....5555
 
Despite the super power this carb delivers, I am a little frightened over the fact, that after only 40 km's my tank is half empty, with my stock carb I would still have about 2/3 left, I can already tell it uses a lot more over the stock, maybe there's a trick to dial it in better, to get better results. I really like this set-up a lot, but if it uses more then double, I might as well stay with the stock carb, I will see in further test, how good it really performs, I will take it off-road over the week-end and will post my impression after that....stay tuned.
 
if any of the circuits are too rich, your wasting fuel
what size main jet do u have?
And possibly the needle or needle jet are worn
 
Its always going to be a trade off to get more power from a 4T with fuel consumption suffering.

Maybe you can get it to squirt less fuel in with the pump?

2T you can just jet them leaner to get some more go :GF
 
Rudi,
I am no expert, but I was just looking at the photos of your new carb and wondered why the locking/adjuster nut on the end of the throttle cable is right at the bottom of the threads. Should it not be above the bracket so you can adjust the play in the cable and lock it in position or maybe tightened against the underside of the bracket, if the bracket has a thread going through it?
 
jon said:
Rudi,
I am no expert, but I was just looking at the photos of your new carb and wondered why the locking/adjuster nut on the end of the throttle cable is right at the bottom of the threads. Should it not be above the bracket so you can adjust the play in the cable and lock it in position or maybe tightened against the underside of the bracket, if the bracket has a thread going through it?
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Jon, yes you are totally right, but it doesn't affect anything, it is just loose, when tightened it secure the seat of the cable. I think it's more a problem of jetting it right and play with the adjustments, with a new carb it always takes time to adjust everything. There's a Japanese guy with exactly the same bike and he had good results with following setup:

· Main jet: # 115
Slow jet (pilot jet): # 45
Jet needle: one row from the top
Air screw: an appropriate position balance is good
Pilot screw: an appropriate position balance is good

I just got it translated via google translate, not the best way, but at least some good information
 
alexuk said:
if any of the circuits are too rich, your wasting fuel
what size main jet do u have?
And possibly the needle or needle jet are worn
Click to expand...

Alex, you're probably very right about that, but I am not a carb guru, so have to check back with my mechanic
 
esspressolungo said:
Alex, you're probably very right about that, but I am not a carb guru, so have to check back with my mechanic
Click to expand...


I found with jetting here in the north my bike ran rich with the hot humid air and altitude.

Dont know about the needle but a #115 main is smallish (modded KLX 140 was #105)and probably about right,pilot maybe a little large,needle...who knows but may need to be leaner,might be worth moving the clip up another notch to see how it runs..

It should be leaner than cold and wet Japan.
 
Loop said:
I found with jetting here in the north my bike ran rich with the hot humid air and altitude.

Dont know about the needle but a #115 main is smallish (modded KLX 140 was #105)and probably about right,pilot maybe a little large,needle...who knows but may need to be leaner,might be worth moving the clip up another notch to see how it runs..

It should be leaner than cold and wet Japan.
Click to expand...

I will have to check again, tried to go up "LMS" with no success today, the carb was bogging and not delivering in the right moments, it's great from the 2nd gear on, first gear its sputtering allover. This carb drinks like a cow as it's set right now. I am sure I will find some solution after fiddling for a while.
 
with the fcr37 on my WRF250 standard main jet is a 170, gets bigger once you add a pipe etc
 
alexuk said:
with the fcr37 on my WRF250 standard main jet is a 170, gets bigger once you add a pipe etc
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Yes indeed. At the moment I try to figure out the squirt timing, the goal is to get it down to 1.3 seconds, that should improve my kilometer range. How much range do you get with your FCR37? This would be a nice comparison to begin with. There's a lot of people in Japan using those FCR's on their XR's, unfortunately google translate is not very accurate and it takes ages to read thru it.
There must be a way to tune the carb, so it doesn't use that much gas and still delivers,,,
 
Just an update about the fuel usage: I rode exactly 30 km's including downhill sections with no throttle use at all, the bike used exactly 3 liters of gas, that gives me a range of 10km/liter, that's insane I think, that's just far to much, maybe I will try to disconnect the pump and see what result I will get.
 
esspressolungo said:
I will have to check again, tried to go up "LMS" with no success today, the carb was bogging and not delivering in the right moments, it's great from the 2nd gear on, first gear its sputtering allover. This carb drinks like a cow as it's set right now. I am sure I will find some solution after fiddling for a while.
Click to expand...

If its OK on the street but bogging up LMS at altitude then you are far too rich. If its happening at the bottom of the rev range I would try a smaller pilot jet first, that will give better response and use less fuel, and then, or at same time I would lean the needle by raising the clip 1 notch.

When the AP squirts is it clearing the carb slide completly? You can alter the timing and duration of the AP.
 
LUFC said:
If its OK on the street but bogging up LMS at altitude then you are far too rich. If its happening at the bottom of the rev range I would try a smaller pilot jet first, that will give better response and use less fuel, and then, or at same time I would lean the needle by raising the clip 1 notch.

When the AP squirts is it clearing the carb slide completly? You can alter the timing and duration of the AP.
Click to expand...
Thanks man, that's some helpful information, I got the carb from Lek and I think they put some strange jets on it, that are sticking out of the spigot, where they should be even on all the pics I saw on the web, I think I will try the "Taffy"mod and will try to adjust the AP, this will have to wait for a couple of day though.

I will try to get some original keihin jets and maybe even the Boyesen Quickshot 3, for adjusting the squirt time from the outside without taking the carb off.
 
I might have the pilot jets but im away until next week.

I wouldnt be going smaller on the main jet though.

I got my Keihin jets from Taipei Scooter Assassins as i they arent available here.
Free and quick delivery.
 
Loop said:
I might have the pilot jets but im away until next week.

I wouldnt be going smaller on the main jet though.

I got my Keihin jets from Taipei Scooter Assassins as i they arent available here.
Free and quick delivery.
Click to expand...

Lew, thanks for the input, just checked it out, somebody told me they got jets in the scooter shop around Chiang Moi, I will check there first. After that I will decided if I order or not.
 
esspressolungo said:
Lew, thanks for the input, just checked it out, somebody told me they got jets in the scooter shop around Chiang Moi, I will check there first. After that I will decided if I order or not.
Click to expand...

Just thinking back i did get the pilot jets i needed here as the ones they use in the PE type Keihin carbs on the little Waves etc fit my PWK carb.

It was only the hexagonal mains i couldnt get here.
 
For now I had the AP disconnected, just to see how the bike runs like that and how the fuel efficiency would improve, I can see a slight improvement, so I think my jetting is too fat and is off a bit, strange enough I still try to figure out the jets, there no numbers on them whatsoever, my guess is somebody tried some other jets and made them fit, I will unscrew them and get the original ones, it's always a bitch to figure out things, when you buy second hand, especially here in Thailand....
 
Just and update about the process, the carb is now in the workshop and will be re-jetted, for now I ride with the stock carb, it feels like I am sitting on a Honda Dream. I hope I will be able to fix the carb some how, as I bought it second hand one never know what to expect, I also ordered a Keihin PWK 35, that should arrive next week, but this will be another thread then.
 
Thanks Lew, I already discussed the issue on TT, there's a lot of info out there, I've read those threads, a real great forum with lot of people with great knowledge about bikes.
 
Rudi,

I don't know what size Keihin jets you'll need but I have a fair stock of them, both PJ and MJ so if you want to try some out let me know.
 
That's what we found inside the carb, 192 jet, 62 jet, Pilot jet cannot be identified, probably someone took Koso or Oko jets, they fit but don't work well. The needle was in the 4th groove from top. There's a few other jets or valves that don't look very original, might need to replace all of that.

From what I understood on the net, most people with stock XR 250 have 40/140 jetting, now I am looking for jets maybe start with 40/135 and then work my way up.
 
esspressolungo said:
From what I understood on the net, most people with stock XR 250 have 40/140 jetting, now I am looking for jets maybe start with 40/135 and then work my way up.
Click to expand...

I have those ones,pilot 30-50 and MJ (hex?) 115-160...sounds like it was way too rich.
 
Rudi, could I try your 192 MJ?
I'm on 180 now and it seems too lean
Do yo know what needle you use?
Dont go assuming its the best one
 
Alex, got some misleading information: here's the right specs:
MJ 112, PJ cannot be read, something like 40 not sure,
Slow Air jet 120, still trying to figure out what is what
The needle was in the 7th position from top, this indicates that the former owner tried to make it more rich, instead of going up with the main jet


When I got the first infos I was on the phone and the connection was bad, so I misunderstood some numbers.

Alex did you try the scooter shop on Chiang Moi? As far as I remember they got Keihin main jets until 200
 
good links- but can I borrow your A/F ratio meter/sensor when you're done?
I dont think they do FCR main jets in chaing moi, I could be wrong
 
Alex, I don't have a A/F ratio meter/sensor myself, my mechanic might, but not sure about that, as for the jets, most jets from Keihin are interchangeable.
 
alexuk said:
I dont think they do FCR main jets in chaing moi, I could be wrong
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I think the FCR uses hexagonal ("hex" same as the PWK?) jets and i couldn`t find any anywhere in Thailand only the round PE types,which there is plenty.

The pilot jets are here.

pwkjeta.jpg


main_jet_1.jpg
 
So here we go again, the scooter shop on Chiang Moi road has pilot jets and main jets from Keihin, we could get everything except the slow air jet, which is not really necessary at this point, I think this is good to know, when you play around with your carb.
 
Did they have the hexagonal jets Rudi?

I thought a slow jet was just another name for a pilot jet?
 
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