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2014 CRF150R, 3500', Summer, 138 Main Jet

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I searched and learned a lot about jetting on older CRF150 (2007&2008 mostly). Not much on the newer models. Stock main is 140. Bike isnt broken in yet. It has been hot and humid where I live at 3,500 ft in the foothills of San Diego. The bike has been difficult to start, after starting it runs but doesnt want to idle without constant throttle attention. Havent had it running long enough to check the spark plug but I assume it is running rich due to weather and altitude. After it runs for a couple of minutes it will only start with hot start engaged. Manual says the jet should be a 138 with all other circuits same as stock. Common sense would say change out the jet, just wondering if anyone else has done this on a NEW 150 with similar environmental conditions and what results they acheived.

 

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The stock main is fine, you need a bigger pilot jet... #40 should be good for you year round, 1.5-2.5 turns out on the fuel screw.

Edit... Stock PJ on on 2012+ is #38, right? That should be good at your elevation. Maybe check needle clip position, should be 3rd Stock, but you could probably drop the needle one position for your elevation. In any case, the main won't affect your idle mixture.

One thing to watch for is the right intake valve likes to close up it's clearance quickly. I've had three of these bike and all three showed the same trend. Keep an eye on your cable clearances, because a tight valve will cause hard starting.

Edited by mjruopp

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Interesting. The slow jet is a 38, manual has that size consistant with all conditions as far as I can tell. There is a PS adjustment to 1 7/8 for my altitude. I will pick up the 138 since they are cheap and see what happens.

Have you tried the db Dawg on any of your bikes?

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