2005 crf250x Jetting Questions

Here is the current jetting

NCYU Needle-clip 2nd from top

Leak Jet 65

Main jet 125

48 starter jet

68 slow jet.

This is a stock CA bike. With zero mods.

Bike starts easy

I would like to jet for approx. 5000ft elevation.

It currently has the off idle bog when throttle snapped open. I am thinking the bog is created by the AP Circuit too lean or rich.

Thanks for your help


Thanks for the Link. that is a good read. I ordered the spring. I will verify the AP Pump operation this evening. do you have any idea what leak jet I should install?

Depends on the type of riding and skill level. Tight slow single track, perhaps a 40, fast, derst riding, a 70. Many are happy with a 50.

Be sure to confirm the oem timing adjustment exactly per the manual. You want to start at a known point.

Here we go with the jetting changes, current setup

Needle 3rd clip

Pilot jet 45

Main 125

Starter Jet 68

Fuel screw 1 turn

no mods to bike.

I have rejetted and the bike runs pretty good, I still have a bog when throttle snapped from just off idle, I think the 55 leak jet will cure that. Only other concern, bike will start without pulling choke, when engine is warm.

I am thinking if I should use a 42 Pilot Jet.

Edited by CO_Ridge_Runner

The bike should require the choke to cold start. The fact you are at 1 turn also makes it appear the pilot might be too large.

Fuel Screw/Pilot Jet

Fuel screw settings in the 'book' are recommended starting points. Every bike is different, as is the temp and altitude. Set the screw according to this method. Do it with the bike fully heated up.

Gently turn the screw all the way in. Now back it out two turns. Start the bike and fully warm it up, go for a 10 minute ride. Set the idle to speed to 1,500~1,800 RPM as best you can (I know, without a tach this is tough, just set it to were it idles relatively smoothly). Once warmed, slow the idle to the lowest possible speed.

*** When turning the fuel screw, keep an accurate 'count' of the amount you are turning it and record it in case you have to reset it for some reason. Makes life easier when you can just set it from notes Vs. going through the procedure again.***

Turn the screw in until the idle becomes rough or the bike stalls.

if it stalled, open the screw about 1/4 more turn. Restart it and slowly screw it in till you can just perceive a change.

If the screw can be turned all the way in and the bike still idles perfectly and does not stall, then you need to go down a size in pilot jet.

Now very slowly, open the fuel screw till the idle is smooth. Blip the throttle, let the bike return to an idle, wait say ten seconds. Confirm it is the same smooth idle.

If the screw has to be opened more than 3 turns to get a smooth idle, you need to go up a size in pilot jet.

If you find it does not stall with the larger jet but has to be open more than three turns with the smaller pilot jet, put the larger one in and set the fuel screw at 1/2 turn.

If the idle speed increased, adjust the idle speed knob to return the bike to a real slow idle speed. You must then re-visit the fuel screw. Keep doing this till the fuel screw is opened just enough to provide a nice steady idle at the lowest possible RPM. Once this is done, increase the idle speed to the normal one for your bike, typically about 1,800 rpm, but go by the spec in your manual.

I installed the 42 Pilot Jet. The fuel screw is at 1.75 turns out. I doesn't start as easy as it did with the 45 pilot jet, but it seems to run as good as it did with the 45. Thanks for the written procedure on selecting the right pilot jet. I guess I might have gotten mixed up in installing the 42 i should have installed the 48 Pilot jet. 48 allows less fuel than the 42 right.

No, 48 allows more. The method I gave you will get you the right jet and the correct fuel screw setting. Be sure you fully understand the logic of the instructions before you implement them.

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