cold weather jetting

[skid jackson]

How much of a fluctuation in tempeture does it take for your j.etting to change?? I've been messing with the 300 (gearing changes and put stock pv cover back on) to get it really smooth. Jetting is a 42 pilot, 180 main on middle clip cck air screw was 2 turn out. about two weeks ago I thought I had it nailed, bike was super sweet to ride, temp was about 60 to 65f. this past weekend i went to a harescramble. It was about 45 and then warmed up to about 50. Cloudy, cool and windy at sea level. In the morning heat it seemed really touchy on the throttle. I figured cool air was making it lean and mean. For the afternoon i turned the air screw in 1/2 turn. It seemed to help a bit but was still on the barky side. One weekend I was loving it than the temp drops 10 to 15 degrees and its back to square one. would 10 degrees make that much of a difference? Would the 42 be kind of lean at say 50 or below that?? Gotta think the 180 in the middle clip should be fine .. no? I'm thinking I'll leave it alone for now as I have an enduro this weekend and the temps are suppose to warm up a bit. I'll run it and see if I notice a difference. any tip for jetting in the 35 to 55 temp range at sea level?? not many rides left but I'd like'm to be as sweet as the one i had two weeks ago!!

 

[dave948]

I'll fatten up my jetting around this time of year. I tend to run a little on the rich side anyway so I don't make a change till it gets about 50 out. Others run right on the point of being lean and 10 deg. will make a differance. Nice cool air makes good power. A 20 deg swing in the summer doesn't seem to do much but that drop bellow 55 -60 seems to make a huge differance.

 

[Eric K]

What year is your GG?

My '01 works better with a #8 slide and my '06 works better with a #7 slide. The '01 was overly senstive to temp & elevation changes with the #7 slide. It works much better with the #8 slide. The '06 was not happy with a #8 slide and works well with a #7 slide. I also use the CCK needle in both.

I ride the high country in the summer/fall. When it gets cool and the snow closes the high country, I go up 1 size on the pilot and a couple sizes on the main jet for cool, lower elevation riding.

 

[skid jackson]

bike is an 06 and has the #7 slide.

 

[skid jackson]

hmm I was looking through a sudco mikuni carb tuning manual today ... it said that if you get spot on at 70f you should be good down to 20f. Its a pretty good tuning manual ... but I kinda wonder about that temp spread!!

 

[Eric K]

If you look at the altitude/temperature jetting compensation chart (see GasGas user manual) there is about a 5% correction factor between 20F and 70F at constant altitude.

My GasGas when properly jetted for 70F is too lean for 20F. I compensate jetting accordingly.

You could jet it for 20F and run rich at 70F. However, performance is sub-optimal and it wastes fuel.