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New CRF250X - Fuel Screw vs Idle Screw Confusion After Jetting

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Hello all,

 

I recently bought a new 15 CRF250X and have completed the CCC mods minus the pink wire mod.  With the help of a friend, we installed the JD Jet Kit which called for 160 main jet, 42 pilot, and red needle.  The directions called for the bigger 160 main if removing the air filter screen which I did.  Lastly, directions called for 1 3/4 turns out on the fuel screw.

 

The bike fired up great but idle seemed a little lagging so I have been fiddling with the idle screw and the fuel screw and have not been able to get it dialed in.  Now I have myself totally buggered (i'm new to all this) on how to balance the fuel screw with the idle screw.  My bike currently is set at 1 3/4 turns out on the fuel screw but is difficult to start and hesitates when accelerating.

 

Is there a starting point on turns out on the idle screw?  And when having idling problems when should I use the fuel screw and when should I use the idle screw?

 

Any help would be much appreciated

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To that I would add that if you find you have some pop on decel (assuming the smog pump is not in the picture), then go a 1/4 turn out more on the fuel screw.

 

Also at the end, you should raise the idle to 1,700 rpms.

 

What your doing is fine tuning the slow circuit.   When your done, you should find you land between 1 turn and 2 1/4 turns out.  If not then you have a slow jet that is too big (<1 turn) or too small (more than 2 1/4 out) and need to change jets.

 

You also can check your end result by doing the following on a warmed up bike at idle:

 

1. Pull the hot start slightly...rpms should rise.

2. Pull it all the way and the bike should die.

3. Pull the choke out and the bike should dies.

 

The reason for #1 is that by following that procedure, you end up slightly rich on the slow circuit.  So leaning things out slightly with the hot start makes the RPM's rise, but really leaning it out by pulling it all the way makes it die.

 

Likewise, pulling the choke makes it way to rich for a warm motor, and it should die.

 

So this check procedure is a nice way to verify that you're setup right if your riding in a lot of different conditions.

 

Good luck with the tuning!

Jim.

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To that I would add that if you find you have some pop on decel (assuming the smog pump is not in the picture), then go a 1/4 turn out more on the fuel screw.

 

Also at the end, you should raise the idle to 1,700 rpms.

 

What your doing is fine tuning the slow circuit.   When your done, you should find you land between 1 turn and 2 1/4 turns out.  If not then you have a slow jet that is too big (<1 turn) or too small (more than 2 1/4 out) and need to change jets.

 

You also can check your end result by doing the following on a warmed up bike at idle:

 

1. Pull the hot start slightly...rpms should rise.

2. Pull it all the way and the bike should die.

3. Pull the choke out and the bike should dies.

 

The reason for #1 is that by following that procedure, you end up slightly rich on the slow circuit.  So leaning things out slightly with the hot start makes the RPM's rise, but really leaning it out by pulling it all the way makes it die.

 

Likewise, pulling the choke makes it way to rich for a warm motor, and it should die.

 

So this check procedure is a nice way to verify that you're setup right if your riding in a lot of different conditions.

 

Good luck with the tuning!

Jim.

 

This is really really helpful.  Thanks a lot.   :thumbsup:

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To that I would add that if you find you have some pop on decel (assuming the smog pump is not in the picture), then go a 1/4 turn out more on the fuel screw.

 

Also at the end, you should raise the idle to 1,700 rpms.

 

What your doing is fine tuning the slow circuit.   When your done, you should find you land between 1 turn and 2 1/4 turns out.  If not then you have a slow jet that is too big (<1 turn) or too small (more than 2 1/4 out) and need to change jets.

 

You also can check your end result by doing the following on a warmed up bike at idle:

 

1. Pull the hot start slightly...rpms should rise.

2. Pull it all the way and the bike should die.

3. Pull the choke out and the bike should dies.

 

The reason for #1 is that by following that procedure, you end up slightly rich on the slow circuit.  So leaning things out slightly with the hot start makes the RPM's rise, but really leaning it out by pulling it all the way makes it die.

 

Likewise, pulling the choke makes it way to rich for a warm motor, and it should die.

 

So this check procedure is a nice way to verify that you're setup right if your riding in a lot of different conditions.

 

Good luck with the tuning!

Jim.

 

I have been playing with the settings and here is what I am finding.  Keep in mind I have followed the JD Settings to a "tee" so a little confused but to get a smooth idle i'm about 3.5 to 4 turns out on the fuel screw.  Also, when I pull the hot start when the bike is warm, nothing happens, idle may dip a little when pulled all the way in but doesn't come close to dieing.  For all elevations JD only offers the 42 pilot so i'm wondering if I am doing something wrong to have my fuel screw 3.5 to 4 turns out.  

 

Any help would be appreciated.

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Did you ever remove the slide?

 

Riders have installed the floating plate upside down on occasion.

 

 

FloatingValve.jpg

 

:ride:

Edited by ramz
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It's not unknown for the fuel screw tip to break off inside the small passage between the fuel screw chamber and the carb throat.  The only way to check it is to remove the fuel screw plus parts on it and look through the chamber to see into the carb throat.  A light and piece of white paper helps.

 

Also, check the order of parts on the fuel screw: first on is the spring, then the washer, and lastly the o-ring.

 

I put a smear of grease on the o-ring, just enough to color in shiny black, so it won't hang up as the fuel screw and parts are re-installed.

 

Not a 250X below, but has the same parts on the fuel screw as the 250X.

 

CarbA08.jpg

 

 

:ride:

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I have been playing with the settings and here is what I am finding.  Keep in mind I have followed the JD Settings to a "tee" so a little confused but to get a smooth idle i'm about 3.5 to 4 turns out on the fuel screw.  Also, when I pull the hot start when the bike is warm, nothing happens, idle may dip a little when pulled all the way in but doesn't come close to dieing.  For all elevations JD only offers the 42 pilot so i'm wondering if I am doing something wrong to have my fuel screw 3.5 to 4 turns out.  

 

Any help would be appreciated.

 

Something is going on....you should be between 1 and 2 1/4 turns out on the fuel screw at most with a #42 slow jet.

 

At 3.5/4 turns out, it will most likely fall out at some point.

 

Check the hot start from lock to lock on the bars and make sure it's not hanging up.

 

If you had the carb out (or don't know that it's never been out or not):

 

1. As Rick said, check the slide seal first and make sure it's installed correctly.

2. Check that the band clamps are tight and the boots are totally seated on the carb.

3. Verify the hot start cable nut at the carb is not cracked.

 

The fact that you need to go so far out on the fuel screw means that your leaner than you should be for some reason.   It may in the end turn out that you simply need a larger pilot jet, but I would be surprised if that was the case.  The setup on these bikes is pretty well known at this point, and 250's don't usually need anything other than a #42.

 

Jim.

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It's not unknown for the fuel screw tip to break off inside the small passage between the fuel screw chamber and the carb throat.

This is especially true of inexpensive aftermarket aluminum fuel screws. OEM as well as high quality aftermarket versions offered by JD Jetting or the R&D Flexjet are brass. Brass is far more durable, also ensuring more accurate metering.

The RD Flexjet is a great way to go for easy adjustments with just your fingers

1461860137053.jpg

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Giving the bike a quick look over, the hot start isn't screwed in above the carb. I'm trying to get to it but a tight fit. May have to wait until I can take it back to to my buddies garage.

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Giving the bike a quick look over, the hot start isn't screwed in above the carb. I'm trying to get to it but a tight fit. May have to wait until I can take it back to to my buddies garage.

 

 Well that would certainly mess you up.

 

Jim.

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Thank you to everyone who offered feedback and advice on potential issues.  The emphasis on the hot start lever led me to find the hot start wasn't even screwed in.  Once properly installed, runs perfect per the JD Jetting specs.

 

Thanks again all,

 

Your time and assistance is greatly appreciated.  

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It's not unknown for the fuel screw tip to break off inside the small passage between the fuel screw chamber and the carb throat. The only way to check it is to remove the fuel screw plus parts on it and look through the chamber to see into the carb throat. A light and piece of white paper helps.

Also, check the order of parts on the fuel screw: first on is the spring, then the washer, and lastly the o-ring.

I put a smear of grease on the o-ring, just enough to color in shiny black, so it won't hang up as the fuel screw and parts are re-installed.

Not a 250X below, but has the same parts on the fuel screw as the 250X.

CarbA08.jpg

:ride:

Thank you for showing me this pic, I was missing the washer and o ring on the fuel screw. This caused idle hang and the fuel screw was unresponsive. I managed to grind down a washer (got creative with a small screwdriver and a grinder) and also ground a larger o ring down to size, put it back together and it now runs great. There is no more idle hang, and I was able to adjust the fuel screw as per the manual. I have ordered the R &D remote fuel screw because I like to tinker with it. Cheers

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Ouch!

 

Glad you found the cause as it can sometimes be a long journey. At least it was for me!

And you will like the R&D fuel screw, to me a must addition to the carb.

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