Math Question about Jetting

[TecateDan]

If I run a 270 Main when it's 70 outside what jet would I want to run when it's 10 outside?? Is there a formula for this??? Oh yea, it's going ot be cold when I go riding this weekend

[Billy Golightly]

General rule of thumb, one jet size for every 10 degrees, in the opposite direction (IE, lower temperature, bigger jet. Higher temperature, smaller jet)

[TecateDan]

Since jets go in incriments of 10 are you suggesting a 330 main jet?

[Billy Golightly]

I'm guessing your using a Mikuni carb. I'm speaking from experience with Keihins which go in 2,5,8,0 increments (IE 182, 185,188,190). If your mikuni jets go in increments of ten, then yes, 330. You might find that to be a bit rich (Depending on how bleeding edge it was to start with) but its a good place to start.

[nd4speed]

I would think more like 300 or 310 but you learn somethin new everyday.

[TecateDan]

HMMMMMM... Well I had my buddy get me a 280 and a 290 so mabey I'll start with the 290 and go from there

[fabiodriven]

It's gonna be 10 degrees and I'm on the fence whether I should do the 280 or 290.

[nd4speed]

As far as I have run my Mikuni I would go up 2 sizes for winter and never had a problem. But I did go 3 sizes when it was below zero with wind chill.

[Headsup]

Yea i would start at 300 at work from there 10 at a time up to 320

[ailll1]

If 70 degrees=270jet size then 10 degrees would be 45 jet size.

You can see how strong I am in maths. A small question like that wont get me wrong.