Cold weather jets for 2008 450X FCR carburetor

Could someone with a 450X, 2008, with an FCR carburetor please tell me which pilot/idle jet you went with along with the main jet, if you had changed it. My BIL's bike is really hard to start and it does not want to idle and the carburetor was cleaned really well by a professional. We think that the jets now need to be changed for the real-cold.

I'd love to know what pilot jet/idle jet you are using in your FCR carburetor as I think that this is what might be the problem with this bike.

I'm wondering if I got a JD Jet-kit that comes with a blue-COLD needle-as the needle position can't be adjusted on the FCR carb and if it will come with different pilot jets that it will solve this bikes problems with starting and idling when cold.

I have a JD Jetting kit as well as a RD Flex fuel screw to make the adjustment so easy.

I also bought a stock muffler on eBay for 85 shipped as the Yoshimura exhaust is just way too loud.

I will put the blue cold needle in and maybe start with a larger pilot/idle jet as the bike is very hard to start and I think that this is the crux of the problem.

At least I am now and expert and getting this FCR carburetor in and out of this bike but I really don't want to do it ever again once I get this bike running.

TYFOON said:

I had a 180 mj in and wanted to see what a fatter jet would do, all I had was a 185. It ran good until full throttle runs in 5th. Then I got bogging. Going down to a 182 and trying again. If it bogs I’ll go back to 180 and go a clip position richer on the needles. I’m convinced a 42 pj is better for easy starts. I’ll report back. Red needle in #5 so far. Also a jdjetting believer.

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Is your CRF450 your snowbike?

Good to know that a 42 has been working as the Pilot Jet for easy starts. That is the problem with this bike as it does not want to start.

Why not the blue needle that the JD jet kit has for cold weather?


I was under the impression that there are NO needle clip positions and that the needle(s) can only be screwed in and out and the reason for the various needles.

The bike has been backfiring for a while which means lean.

The RD Flex Fuel Screw is also coming today, that will help in dialing in the idle/off idle response.

TYFOON said:

Yes, there is a Camso kit on my 450R. There are 5 if not 6, I can’t recall, on the jd needles.
Also I don’t think red and blue is hot or cold persay but allow for 1/2 step rich to lean settings. The taper of the blue is a richer taper so maybe so. Yes I’d stick with the 42 for sure. If it’s hard to start still, measure your intake valves.

I’m putting in the 182 today and will test again.
I want to get the mj as close as possible before I go back to fine tuning with the needle.

Jd recommended the red#5 to start so that’s where I’m at.

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Thanks, again, TYFOON. Good to know you have the same bike and track even.

I'll have to pay attention to both the clip positions as well as whether to choose the red or blue needle in the JD jet kit.

I'm going to have to find the jets I had taken out of the carb as I had gotten a rebuild kit and not even thinking that the jets might be different, just put the new ones in with no regard as to what it might do to the way the bike runs. The bike started so I stuck with whatever was in there but as time went on, the bike would backfire more and more=lean.

I had sent the drasted FCR carb away, paid $200 and had it cleaned.

Sometime Saturday, Saturday night, I should have the carb off-again(if this bike runs good I won't mind never having to take this carburetor off ever again), replace what I need to replace, clean anything that might need cleaning, install the RD Flex fuel screw and hope that when I get it back together it runs again.

The OEM muffler-used, should come on Tuesday as the bike has this obnoxious Yoshimura on it now that is nothing but loud and I think the carb is lean because of it. The airbox had also been cut and opened by the previous owner.

Thanks for all the help again guys.

I can almost see the finish line with this bike.

Here is the whole story to date.

BIL buys the bike last winter. It starts, it runs, for a month or two.

One day it does not want to start. I clean the carb as best I can and the bike starts and runs again. Not long after, the bike is backfiring like crazy. I had taken the carb on and off so many times, it is now actually easy to me.

Here is the short of it; the fuel screen in the tank degraded and sent all the plastic parts/crystals into the carb, clogging it all up.

Here is where the jetting was all messed up. The bike has a Yoshimura full system, RS-S. It came jetted with a 158 main and the needle clip was in #4. Because I didn't know squat about jetting, I just took the main jet that was in the All Balls carb rebuild kit and stuck it in. That jet was a 145-small.

I put the aluminum fuel screw in not knowing about either the spring, the washer or the o-ring. I can't even remember what order I put them in or if I even did put them in.

The bike would start but not run correctly in my basement this past summer. It would not start the past two weeks.

I get a JD jet kit and an R&D Flex Fuel Screw.

The blue cold needle goes in in #4 clip position.

165 main jet.

Fuel screw 1 1/8 turns out-making sure the spring, washer and o-ring go on in that order. I had learned that alloy fuel screws do not hold in the aluminum body and when I went to take the fuel screw out, somehow the o-ring had gotten itself 1/2way down the shaft of the screw=air leak.

I also had the idle screw so far out that it was nowhere near the throttle cam to adjust the idle. I had set it to right where it touches the throttle cam.

I put it all back together and with choke-out, the bike fired right up and idled perfectly. No hunting, no hanging, no surging, no stalling, no backfiring(yet). PERFECT!!!!


Now I need to get the bike on the snow, all warmed up before I even think of fiddling with the fuel screw, if I do at all.

It is amazing the bike ran at all last winter with a 145 main, never mind the 158.

I did find a 45 pilot and it had a 45 pilot when we got the bike.

I tried to get the Yoshimura head pipe off the exhaust studs but the exhaust flange on the pipe did not want me or give me the space to get the flange off the studs or I'd order a new OEM header pipe as I had already spent $85 on the OEM muffler. How to get this header pipe and the exhaust flange off the studs?

Interesting response from JD.

As I have probably mentioned so many times, we went whole-hog as we got the bike used and some serious crap had been run through the entire fuel system so the carburetor got a thorough cleaning from KeihinFCR.com-who cleaned and then replaced all the seals, gaskets and o-rings in the carb and made sure everything was adjusted correctly.


Pilot jet is a 45.

Started with the R&D flex fuel screw at 1 1/8 turns out.


Put the JD jetting blue needle in and on the 4th(middle) clip.

165 main jet.

The bike now starts up easily and a few seconds after, when the idle starts climbing, the choke goes off and the engine idles perfectly, like it should.

Hopefully all you guys need is to give the carb a good cleaning and to maybe change a needle or jet here or there. We are good as the bike had started and had run all last winter, despite the FCR carb being filthy and all the wrong jets/needle installed.

Last season, even with the FCR carb having missing the following;

1. Plastic hot start nut-causing the engine to run lean=backfiring

2. Fuel screw-vibrated out of the carb-again, lean=backfiring

But the bike would still start and run, backfiring and all and that despite all the brutally cold temps, there was never too much of a problem with starting-although every time the bike needed to be re-started, the choke had to be pulled out, it always started back up. The bike does have the PST engine jacket but no cold weather panel to close off the space above the exhaust pipe on the clutch-side of the motor. The engine always seemed to keep the heat in so the carb would not ice.

I never once tried to access the jets by simply turning the carb sideways-towards the gearshifter side of the bike, it never occurred to me to even try it as I would always just go through the entire routine of removing the seat and loosening the subframe to tilt it up so I could get the entire carb out.

The FCR carb is so big and really just tall, that it needs all the space in order to get it out and I'll bet that on that KTM it is all really tight as the CRF had the big aluminum frame spars in the way but once the fuel tank was off and the subframe tilted up a bit, the carb came out pretty easily.

I hope you get it sorted. If you can get the carb turned so you can just get the pilot jet cleaned, hopefully that will be all it needs and that there is all sorts of crud inside of it that once gone, will allow the engine to start easier.

The fuel screw is another place where the it has to be adjusted from 1 to 1 1/2 turns out for the bike to start easier. Same with the idle screw, it needs to NOT be turned too far in to increase the idle or the bike won't want to start.

It sure is an odd response from JD Jetting.

There is a cold weather needle after all and other than that, just some main jets in the kit.

I had/have to figure that if the bike ran with a filthy carburetor along with old/degraded seals inside, and with jetting that was way off, a needle that has been tuned for cold weather is going to make a big improvement and so far, it has.

In all my reading on the FCR carburetor, there is only one other needle that is mentioned in the NVCS or something like that but I have not seen anything specific to the cold and snowbiking.

There was a beautiful revelation yesterday morning.

My nephew, Sam, gets the 450X started. He only knew to pull the clutch in and to hit the starter button. Later in the day, as I was impressed at how he got the bike started, he said that he just pulled in the clutch and pressed the button and the bike fired right up.

"Did you use the choke?"

"I don't even know where the choke is."


My gosh, that is just too funny. So the secret is, when it is cold, just don't even use the choke. That the carburetor is setup such that the bike will just fire up and idle first start or first cold start, or make that every start, with no choke. Whatever it means or how it is doing it should not matter, right? That the pilot jet and fuel screw setting must be correct and to just enjoy easy starting again with the button. Ahhhhhhh.