Jump to content
Sign in to follow this  

Winter Jetting

Recommended Posts

Shouldn't be any need to change it unless you are running some ultra high performance setup. 😉

Share this post


Link to post
Share on other sites

Depends how crisp you want your bike to run. If you're riding in 40 to 60° temperatures vs 70- 100° temperatures, you definitely can afford to go a little more rich on the jetting. If your jetting is stock it's probably pretty good for winter and a little rich for summer temperatures

Edited by 15YZ250

Share this post


Link to post
Share on other sites

2 or 4 stroke ?   A 2-stroke is more finicky to temperature changes.

 

Also depends on what is the difference between your 'summer' ambiant temps and your 'winter' ambiant temps.

 

Say your engine is jetted perfectly to run at 20°C average in summer, due to increased air density,

down by 5°C it will require some fuel enrichment to maintain the same air/fuel ratio.

 

The service manual for a late model YZ125 indicates a jet change / adjustment

is required for every 10 to 15°C increase or decrease in ambiant temps, which is

what I've found to be accurate when fine tuning for late fall daily temperature swings.

Share this post


Link to post
Share on other sites

Mine isn't ultra high performance yet I had to change my main jet to a 45 from 42 then change the position of the clip to two positions more, down from the top. I needed to richen it.

Plus with a jd kit. If needed, they actually send a blue needle which is for I think, 30 and below.

But just remember, if you're having problems when throttling down and it's at the first quarter turn then it's your pilot, mid range it's your needle and high it's your main.

Edited by Crispy_Fruit_Loop
  • Like 1

Share this post


Link to post
Share on other sites

Unless you are going from perfect jetting at 110* and then riding in 0* you aren't going to notice it, unless you are going from a very dry hot climate to a very humid, very cold climate.  Cold air is denser, and cold humid air is even denser, that's why muscle cars always seem to run better on cool, damp nights.  But for 99% of riders and drivers you won't notice a difference, but if you want to rejet to slightly richer it isn't going to hurt anything.  Personally, I've never bothered.

Share this post


Link to post
Share on other sites

I have a modern 450 and I can tell by the way it idles when it needs a cold weather tweak.

With the RnD Flex Jet, it is 2 turns out in summer, 2.5 turns out in 30-50 deg, and 3 truns out in the fridgid cold.

 

I don't spend enought time in the mid to wide open throttle to notice a main jet or needle difference.

Share this post


Link to post
Share on other sites

2 or 4 stroke ? A 2-stroke is more finicky to temperature changes.

Also depends on what is the difference between your 'summer' ambiant temps and your 'winter' ambiant temps.

Say your engine is jetted perfectly to run at 20°C average in summer, due to increased air density,

down by 5°C it will require some fuel enrichment to maintain the same air/fuel ratio.

The service manual for a late model YZ125 indicates a jet change / adjustment

is required for every 10 to 15°C increase or decrease in ambiant temps, which is

what I've found to be accurate when fine tuning for late fall daily temperature swings.

its an 03 RM250. i live in canada so its about -20 Celsius right now. Bike has power on the bottom end but none on the top. Some in the middle.

its an 03 RM250. i live in canada so its about -20 Celsius right now. Bike has power on the bottom end but none on the top. Some in the middle.

oh yea, and in the summer it can go 20 to 30 celcius

Share this post


Link to post
Share on other sites

On my carb 4 stroke, I notice elevation changes more than temp changes here in the NW. I don't bother other than maybe a slight tweak to the fuel screw if the temp drastically changes.

Share this post


Link to post
Share on other sites

On my carb 4 stroke, I notice elevation changes more than temp changes here in the NW. I don't bother other than maybe a slight tweak to the fuel screw if the temp drastically changes.

ooooo yeh! Fuel screw! But if it's all the way out then time to rejet 😛
  • Like 1

Share this post


Link to post
Share on other sites

Basically do what works for your bike. But like I said before. With my bike, I had to go from a 42 to a 45 and I believe I'm on the fifth clip position. I'll take a look at my notes.

Everyone is being my parrot today 🙂

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×
×
  • Create New...