Summer Jetting

[Monica]

Need to get a little guidance on tuning the carb for the summer. I been noticing the bike won't start as easy when it's warm after a gas station stop unless I give it a little gas when I hit the magic button. Otherwise the bike is running fine on the road. The ambient temp has gone up since I first tuned this bike in the winter of Texas. Now it's 20* warmer at least.

Do I need to richen the pilot mixture? (and subquently go from there?)

TTR125LE w VM24 carb

 

[bwdmax]

You are actually giving it a little air.... so you need to lean the pilot mixture a little. You probably can just use the mixture screw to get enough adjustment.

 

[RollingJ]

I just had to drop a size on by pilot jet, I have a 38 in now. My pilot screw was at 3/4 of a turn out and the bike would start cold without choke, so it was time.

 

[Monica]

Ohhh yeaa that's right, pulling the throttle opens the slide and giving more air on the starting up circuit.
Ok, I'll recheck/adjust the air mixture screw - thanks!

It makes sense, if I remember right, I had room to spare (as in running a hair richer already) as I have tuned to 1.5 turns out.

Thanks guys

 

[texas123]

Question:
Why would ambient temperature affect the fuel mixture setting? I thought the mixture screw was set to air density & not air temp.

 

[Ed M]

Air density is affected by many factors such as temperature, altitude, humidity, air pressure etc. 20 degree air is denser than 100 degree air, if you are jetted close to perfection for 100 degree air temperature, then your jetting will be a bit on the lean side at 20 degree air temperature. I think most manufacturers jet for 70 degrees, very little altitude, and not sure about humidity or air pressure.