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Ben500RR-S

2008 450X cold weather jets. Which ones?

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Hello all,

 

My BIL got himself a 2008 CRF 450X.  It has the stock FCR Keihin carburetor on it.  

Could you please tell me which idle/pilot jet to get for cold weather as well as which main jet for cold weather?, like below freezing for the snowbike.  

 

Stock header pipe and stock muffler.  

We're having a lot of trouble getting the bike started and keeping the motor running now that winter is here and feel it must have to do with the jetting.  

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Only 1,000', maybe 1,500 at the most so pretty much sea-level from what I understand.  

Need to go richer on both the pilot/idle jet as well as the main?  

Needle and clip position?  

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165 summer, 168 winter. 45 pilot year round.

Fuel doesn't atomize as well at 40 degrees, so even with perfect jetting, cold starting can be a chore.

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22 hours ago, Leardriver said:

165 summer, 168 winter. 45 pilot year round.

Fuel doesn't atomize as well at 40 degrees, so even with perfect jetting, cold starting can be a chore.

Thanks.  At least I'll have a direction to go in.  

I have realized that it is probably the pilot/idle jet that needs the help.  I suspect it is just too small right now, or is clogged again somehow.  

It was starting a LOT better last winter, even before the carburetor was ever cleaned but I realized that I had changed the jets to whichever ones came in the carburetor rebuild kit I had gotten.  I really should have both cleaned and replaced the jets I had taken out as I think that this has been the main problem, that and the fuel screw that is buried under the carb.  Even though there is an aftermarket one it is not easy to get at and turn. 

 

I do have a JD jet kit as well as the RD Flex Fuel Screw so I think that between the correct jets and even the new cold weather-blue needle, and the fuel screw that I can adjust as easily as the idle screw, I might finally have this bike starting easier and idling normally.  

 

With the Yoshimura pipe on the bike-it came with it, it has been backfiring like crazy ever since I had replaced the jets.  I suspect that I put in smaller, stock jets when I had changed them. 

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I had taken about 1 hour this morning to read all the threads on 450X and Jetting so I have a pretty good feeling that between swapping to the JD Jet blue "cold weather" needle, installing the RD Flex Fuel screw, making sure that the pilot jet is clean as well as the passage above it, that I should get this bike started and idling like it was before. 

 

I have a stock muffler that will be coming on Tuesday but I'll pull the carb and install the stuff on either Saturday or Sunday, after a good ride.  

I think what is probably the biggest problem is that I have not been able to fiddle with the fuel screw as it is buried under the carb. That and I had tested the engine when it was warm and not 30-40-F like it will be this weekend.  

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Main jetting and needle position won't influence starting at all. I buy 10 packs of #45 pilot jets, and just put new ones in at the spring recommissioning time.

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I finally found the pilot jet that I had taken out of the carburetor and it is a #45. 

I also have the bike here in the garage as well as the JD jet kit and the RD fuel screw.  I will have my work cut out for me this upcoming week as I need to get this bike running again. 

An eBay stock muffler is also coming tomorrow.  

 

I have the subframe up, the fuel tank out and just need to take out the hot start nut to get the carburetor out.  Maybe after work I'll have it out tonight and can get started on the open heart surgery. 

Edited by Ben500RR-S

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Thanks again for all the help.  The bike is now running and idling again.  Here is the story that had started last winter. 

BIL buys this 2008 CRF 450X.  I know nothing about this bike.  The airbox top had been cut out along with the exhaust side of the airbox.  

I put Camso 129 kit on along with a Thermobob-thermostat with bypass.  The bike starts and runs.  

After a short while, the bike gets hard to start and it backfires a LOT.  Shortly after, the bike just won't start.  I take the carburetor off.  I clean the carburetor and put it back on.  It starts again but the backfiring never goes away but gets worse.  I take the carb off and put some of the All Balls carburetor rebuild kit parts in the carb.  I know nothing about jetting and didn't bother to read up on it like I have this past month.  

One day, when going over the carb, I find the end of a fuel screw all ground up by the C/S-sprocket.  I then put the new fuel screw in but had no idea that it needed a spring, washer and o-ring on the end of it.  The bike started but still backfired and the engine would hang the idle, be hard to start, it became a hot mess.  Eventually it would not even start.   

This past summer, I sent the carb out to FCR.com and he both cleaned and replaced all the wear parts and the seals/o-rings/diaphragms that needed replacing and he did a great job.  

 

There was a 45 pilot in the bike from the All Balls kit.  There as a 45 in the carb when we got it.  I left the 45 in but just made sure it was/is clean.  

 

There was a 145 main jet from the All Balls kit.  The bike came with a 158, probably to go with the Yoshimura pipe-I have no idea and  still don't know if that is/was the right jet for that muffler.  I put a 165 main jet that came with the JD jet kit and that was recommended to start with at sea level to 3,000'.  

 

I put the blue needle in the 4th/middle position in.  

 

I put the RD flex fuel screw in correctly and turned it 1 1/8 turns out.  I think this fuel screw has been one of the biggest things I  have overlooked in this whole ordeal.  Even tonight, the o-ring for the screw was 1/2 way down the shaft of the All Balls fuel screw so there is no way it was working like it should/needed to.  Now with a known good flexible fuel screw, to be able to adjust for the conditions is going to be exactly what has been needed.  

I turned the idle knob to get the bolt nudged right up to the throttle cam so if I turned it clockwise, the idle would increase.  Before, I had turned the knob so far that it would have taken me so many turns before the bolt would even touch the throttle cam, I now have it so that as soon as I turn the knob in, it will increase the idle.  It is so nice hearing the bike just start and as soon as it starts I can turn the choke off and the bike wil just idle nice and clean and steady and when I rev the engine there is no backfire(ing) and no hanging idle.  

I finally did it.  

I now just need to wait for the used stock muffler to come tomorrow and see how the bike runs with that muffler.  I know we will LOVE the peace and quiet we will have compared to the obnoxious Yoshimura that has been on there.  

 

I will also wait until it gets a LOT colder out as it was in the 40's tonight so the true test will be when the bike is back on the snow but at least the bike fired right up.  I'm so glad it is not the intake valves or the decompressor.  

 

 

Thanks for all the help.  

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I now just need to wait for the used stock muffler to come tomorrow and see how the bike runs with that muffler.  I know we will LOVE the peace and quiet we will have compared to the obnoxious Yoshimura that has been on there.  

 I run mine with a #165 with stock exhaust and don't have any issues. That is during the warm months though.  Still, you should be OK with the 165 in.

Jim.

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This bike is firmly in the cold.  It might never see dirt again.  

I have to figure this;  if the engine somehow ran on the 145 main that was in there most of this past winter, and the sled had started on a 158, going to a 165 is going to be like a revelation.  

 

That and the JD Jetting blue cold needle should help a ton. 

Even though it is not my bike, I'm excited to hear how the bike sounds with the stock muffler.  I like and want quiet. 

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The 450X is now running perfectly  I am almost astounded at how well the bike is both starting and running.   

Here is what the bike had needed since day 1. 

Hot start nut-replaced with an Aluminum one.  

R&D flex fuel screw, now 1 1/2 turns out.  

JD jet kit.  Blue cold weather needle set at the 1/2 or 4th clip position out of 7.

 

165 main jet. 

 

The bike now starts when it is cold and NO choke is necessary.  It fires and idles perfectly.  No backfiring, no stalling.  No bogging, no nothing but just good, clean-running.  

Between replacing all the parts I did and the professional cleaning and the replacement of all the worn out parts inside of the carburetor, the FCR Keihin carb is now mint and should be good for a long-long-time.  

 

Thanks for all the help. 

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The bike now starts when it is cold and NO choke is necessary.  

That's a bit odd, but if it's running good, it's running good.

Jim.

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On 12/26/2018 at 7:43 AM, Jim Dettman said:

That's a bit odd, but if it's running good, it's running good.

Jim.

Later that night, when it was colder and below 30, we had to use the choke to get the bike started.  

I had realized that during the day, when the temp. was just above freezing with the bike sitting in the sun with no wind/breeze, the engine was able to start with no-choke but once it was cold, the bike needed the choke to start.  

That the engine is starting so easily and running so well is great.  

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The 450X ran flawlessly all day yesterday.  

I had tried 3 starts with full choke with the bikes battery and had then used the jump pack and by the third attempt, the bike had started-it had been starting and then dying-probably due to the cold as it was in the low 20's yesterday morning, but once it fired up and ran on the choke with a high idle for about 30 seconds, I could then turn the choke off and the bike would keep a perfect idle.  

The bike would start for the rest of the day by just pulling in the clutch and pressing the button-ahhhhhh, HONDA! 

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A true cold-weather test happened yesterday and I had failed the first part of the test.  

It was 2-3F.  Even with a jumper pack and then cables from a running snowmobile, I could not get the 450 to fire.  I had given up and my BIL rode his KTM300. 

We had come back a couple of hours later and I had realized that I should try priming the carb by turning the throttle fully a few times and while I was doing so, I could hear the fuel squirting in the carb and when I tried starting the engine, I was getting combustion.  After just a few more tries with the engine trying to start, it started and stayed running and ran great for the rest of the morning, until 1pm when we had to stop. 

 

The lesson for the extreme cold, that twisting the throttle slowly, primes the carburetor so the engine gets the fuel it needs to start.  Once the bike was started, it then started very easily on the button for the rest of the day. 

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2 Degrees is pretty cold for any engine and yes a little gas does help, but be careful.   It's easy to flood an engine like that in the cold.   gas just doesn't vaporize all that well when it gets really cold, plus your not turning over well, which was probably most of your problem.  That's why a lot of equipment use block heaters.

And I'd say that despite what you think, you have it dialed in as well as you can for a carbureted motor.

Jim.

Edited by Jim Dettman

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