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Does this seem odd...CR250R Jetting

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Hello All,

First post here so take it easy on me.

I recently bought a 1999 CR250R that had been stored...it was basically new with very very few hours on it. Last night I decided to dig into the carb to determine what it had in it for jetting, here is what I found.

Main Jet 168

Slow Jet 40

Needle 2nd from top

Air Screw 2 turns out

Bike was always at my altitude in Central Oregon 3200' give or take. Last I rode it (Before we had 3 feet of snow) it ran awesome. Temp out were mid 50's

As per the OEM Serivce Manual, for that temp and altitude, it says it should have the following;

Main Jet 188

Slow Jet 42

Needle 3rd from top

Air Screw 2.25 turns out

Should it be this far off?? The smallest Main Jet the book listed is a 175 and a 42 Slow Jet across the board. It just seems that what is in it now is quite lean except for the Needle position, but it runs great.

I am getting ready to go ride at a lower altitude (1000 to 1500 or so), Temps will probably be in the mid 40's or so I'd also like to get feedback on what to change it to from what I have now for this condition. I have ordered a 170, 172 and 175 main jet and a 42 slow jet to prepare for the coming ride.

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Hello All,

First post here so take it easy on me.

I recently bought a 1999 CR250R that had been stored...it was basically new with very very few hours on it. Last night I decided to dig into the carb to determine what it had in it for jetting, here is what I found.

Main Jet 168

Slow Jet 40

Needle 2nd from top

Air Screw 2 turns out

Bike was always at my altitude in Central Oregon 3200' give or take. Last I rode it (Before we had 3 feet of snow) it ran awesome. Temp out were mid 50's

As per the OEM Serivce Manual, for that temp and altitude, it says it should have the following;

Main Jet 188

Slow Jet 42

Needle 3rd from top

Air Screw 2.25 turns out

Should it be this far off?? The smallest Main Jet the book listed is a 175 and a 42 Slow Jet across the board. It just seems that what is in it now is quite lean except for the Needle position, but it runs great.

I am getting ready to go ride at a lower altitude (1000 to 1500 or so), Temps will probably be in the mid 40's or so I'd also like to get feedback on what to change it to from what I have now for this condition. I have ordered a 170, 172 and 175 main jet and a 42 slow jet to prepare for the coming ride.

your bike is jetted lean for the higher altitude, i would go closer to stock for lower altitude riding. How does the bike run?

If your concerned about your settings do some runs and check your plug.

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your bike is jetted lean for the higher altitude, i would go closer to stock for lower altitude riding. How does the bike run?

If your concerned about your settings do some runs and check your plug.

Thanks bcislandrider,

 

The bike runs great, no complaints at least in my conditions...it is just so far different than what the manual states for my altitude and temperature that it was a liitle shocking.  I honestly don't know what it will like at the lower altitudes if we get to go this weekend...(might snow).  Anyway, I have a 170, 172 and 175 MJ coming and a 42 SJ as well, hopefully one of those will be the right one for the change.

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Thanks bcislandrider,

The bike runs great, no complaints at least in my conditions...it is just so far different than what the manual states for my altitude and temperature that it was a liitle shocking. I honestly don't know what it will like at the lower altitudes if we get to go this weekend...(might snow). Anyway, I have a 170, 172 and 175 MJ coming and a 42 SJ as well, hopefully one of those will be the right one for the change.

i run 42 - 175 at sea level to 1000+ feet elevation.

The choice of needle can require way different jets than recomended.

Try and confirm what needle your running. Id rejet to stock and fine tune from there. Sounds like you have the right idea anyways.

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i run 42 - 175 at sea level to 1000+ feet elevation.

The choice of needle can require way different jets than recomended.

Try and confirm what needle your running. Id rejet to stock and fine tune from there. Sounds like you have the right idea anyways.

Dang, thats the only thing I didn't confirm when I had it a part...what the heck was I thinking.  Ok, I will check it later today and see if things start to make more sense.  A friend of mine that will be riding with me when and if we go down in altitude thought it would take the 175 there so you running a 175 seems to be on track with that.  If we get out, I will post with my findings.

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Dang, thats the only thing I didn't confirm when I had it a part...what the heck was I thinking. Ok, I will check it later today and see if things start to make more sense. A friend of mine that will be riding with me when and if we go down in altitude thought it would take the 175 there so you running a 175 seems to be on track with that. If we get out, I will post with my findings.

have u considered a JD Jetting kit? They work great and they provide excelent advice on jetting. The kit is really two different specially designed needles and a few standard jets.

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have u considered a JD Jetting kit? They work great and they provide excelent advice on jetting. The kit is really two different specially designed needles and a few standard jets.

Just looked at the kit and it looks interesting...perhaps I'll try it after I figure out what I have going on now. Haven't got out to check the needle yet...got wrapped up watching NASCAR tonight...plan on going out after the race.

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Dang, thats the only thing I didn't confirm when I had it a part...what the heck was I thinking. Ok, I will check it later today and see if things start to make more sense. A friend of mine that will be riding with me when and if we go down in altitude thought it would take the 175 there so you running a 175 seems to be on track with that. If we get out, I will post with my findings.

Needle is stock R1370DKA clip, second notch down from top...book calls for 3rd position...so this is even leaner yet correct?

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There is a sticky I saw for jetting under the stickies on this forum for jetting / fuel injection. Pretty much let the bike idle and twist the air / fuel mixture screw till you get the highest idle. If it idle highest at under 1 turn you need a larger jet. If it idle highest after 2.5 turns I believe you need the a smaller jet. It might be vica versa on the sizes. Then for the main do throttle chops. Find a very long open area, run the bike through the gears at full throttle pull the clutch in and kill the bike and come to a stop and inspect that plug. The color and everything will tell you what size to go too. I did this a few years ago before I was a member and saw the post here. It works great. Try doing this at sea level or lowest you can get on the coldest day possible. Then when it warms up you will never be lean. Always better to run richer then leaner.

Good luck,

Chris

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Keep in mind there are variables involved when jetting a 2t & the manual will provide a suggested starting point based on temp / altitude on a stock bike.  The settings will be slightly on the rich side since the manufacturer wont suggest a setting on the borderline that can cause a lean seizure.   It's good to start on the rich side & lean accordingly than the other way around.   

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Well we didn't get to go ride and test what would be needed for the elevation change so it will have to wait until next time. I will report when that happens.

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Finally got to take her down in altitude to ride this weekend and here is what we found;

Altitude - 1500 - 3000

Temp - 48 °F (roughly)

Raining heavy at times

MJ - 172

SJ - 42

NC - 3rd

AS - 2 out

Bike ran great, lots of power (way more than at home 3250 ft). Was a little rich for the first trip down so that was good...didn't get to lean. As we approached higher altitudes though, I had to clean it out from time to time, especially after long down hills on the trails but happy it ran fine and was not to lean. Same conditions next time and I would probably only change the MJ to a 170. As a matter of fact, I'm going to try the 170 at home before I change anything back and see if I can take away a little concern of running to lean here.

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