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crf250r 280 big bore jetting?????

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HELP! I have 07 crf250r with a cylinder works 280 kit. everything else is stock. where do I start with the jetting? one person says go leaner one say go richer. its hard to start when cold and actually helps to pull the hot start. tells me I need to lean it out somewhere. also at wide open in fifth gear ,once I top out it feels like im running out of fuel in the carb. is that possible? I know what hitting the rev limitter feels like n thats not it. I ride to have fun I dont race and I probably dont ride a four stroke correctly but I have fun. my elevation is at sea level. any starting point would be great. thanks:bonk:

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Ride your bike and test it. A s Craig alluded, typically, you need to go leaner on the jetting with a bigger bore.

This will get your fuel screw and pilot jet right:

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.

Then you need to select the correct main (7/8ths to WOT under load) and then work on the needle diameter and finally the clip position.

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