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09 CRF 150R - runs fine at wide open but misses like crazy in the mid range

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I have the exact same issue with my boys 09 CRF 150R right now. it doesnt start until it gets hot like 4 or 5 mins of riding. It has a 140 main and a 42 pilot with a QS3. It runs fine at wide open but misses like crazy in the mid range. I had the valves checked this week and they are within spec. Need help we race this weekend.

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Too rich on the needle if it gets worse with the bike getting hotter.

I just left my dealer and they are sure it is lean when it gets hot??????

See if they get it fixed before I have toleave tomorrow?

Thanks for your input.

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Your dealer is dead wrong.

A cold engine needs a richer mixture. If the bike was lean, it would be too lean when cold and would get better as it heats up (a hotter engine needs a leaner mix than a cold one-hence a choke on cold starts). Your mid throttle miss will remain.

Hard hot starting could be too rich on the pilot or fuel screw or the float height is too high. The dealer might guess right on this.

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I agree with you i have run sleds for alot of year and the hotter it is the leaner you need to go. doesn't matter what it is? so if that is the case I should raise the clip 1 notch to drop the needle right?

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I would raise the needle probably two clip positions (towards the top/flat, to lower the needle).

The hard hot starting is either a too far open fuel screw and/or a too large a pilot.

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.

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Thanks a bunch with the info. I will see how they make out and I am thinking not good. I will try your suggestions.

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