The CRF150F comes from Honda very lean in the idle circuit and this makes starting a cold engine very difficult .
The following change to the bike will give you a mild boost in power as well as a much better running 150F , that will start easier and actually IDLE without stalling .
and it will only cost you about $40
You will need the following items :
-99103-KPT-0420-Slow jet (42 being the size, stock is 40)
-99113-GHB-1150-Main jet (115 being the size, stock is 98 )
A good hi flow air filter like a twin air or no toil or uni , etc , etc.
You need to start by removing your seat from bike .
1. Remove the rubber snorkel from airbox , just grab it and yank it off .
2. Remove the baffle from the end of the exhaust pipe , drill a few 1/4 inch holes in the solid steel plate on the inside end and reinstall it in bike , Now it will breathe a little better and you will still have a quiet bike .
3. unscrew the cap where the throttle cable goes in the top of carb .
4. pull the cap and slide that is attached to the cable staight out .
5. now you can change the needle , but you really don't have to change it just move the clip to the fourth notch from the top of the needle if it isn't already there at the fourth notch.
If you do want to change the needle use part number -16012-KPT-921-Needle set (on the middle clip) .
6. unscrew the band clamp on the air boot at the rear of carb , remove the two 10mm nuts that hold the carb to the intake manifold .
7. now you can remove the carb from bike (make sure to unhook the vent tube from the clip on the frame
8. Turn carb upside down over a bucket and gas will drain out .
9. remove the philips screws from the bottom of the carb on the float bowl , remove float bowl and you can now see the main jet and it has a little plastic pc. around it that has a notch in it for the pilot jet clearance
10. replace the main jet and pilot (don't overly tighten or you will break them off in the carb body, not good)
11. reassemble the reverse of above and you are done except for fine tuning the fuel screw after you get the bike running .
12. Replace the air filter with a new one , like a twin air or no toil etc. don't use the sponge that honda sends with the bike
you're gonna like the way it starts and runs now !