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05 crf 250 just had new crank and piston, but not starting.

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I have just finished rebuilding it, has had a new mitaka crank and conrod and also a new genuine piston kit, but I cant seem too get it too start. It starts occasionally but takes 10 minutes of kicking too get it going. I took it out for a while once i got it running, but when i stopped and tried too get it going it wouldn't go yet again. I then checked the clearances and adjusted them thinking that that was the problem but put it all back together and it was still the same. checked the timing and all is okay. It has just had a new iridium plug too. Does anyone know what it could be as i have spent ages trying too get it going right and cant seem too find it. Thanks.

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What is your starting procedure? What is your current jetting? What is the weather like there? Temp? Was it hard to start before you rebuilt it? Give us as much info as you can so its easier to help you.

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couple twists of the throttle then kick, it used too start first or second kick hot or cold before rebuild. Im afraid i dont know what the current jetting is. Weather is damp and about 10-15 degrees. Been informed from a friend that it will be the carb if the valves are fine, so i'll strip it and give it a good clean and see if i can set it up correctly. Thanks.

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When its colder you may need to give it a couple more twists of the throttle to help it start. I twist mine up to 6 times to get mine going when its really cold. Also colder weather will require slightly richer jetting. Probably one size bigger on the pilot and main jets. If your timing and your valves are in spec then look at the carb.

I always write down what jetting works best for my bike depending on the weather conditions. When its blazing hot in the summer I run as low as a 38 pilot and 168 main. And when its colder like now I go to a 42 pilot and a 170-172 main jet. Weather is a very important factor when jetting. Temp, Humidity and Altitude all have to be considered.

Having the idle set properly is one of the most important factors in easy starting.

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Thanks very much, you've been very helpful. I have stripped the carb tonight, cleaned all my connections and put it back together and it started after a good few kicks, it's starting much better but not as well as it used too. the pilot is 42 and the main is 172. Temps here are ranging from 40-50 degrees fahrenheit too. Should i up it too a 45?

Thanks.

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