2 Stroke Questions about jetting

Jhutchh

Jhutchh

I hate to be asking a question that sounds so simple, but I see alot of you guys REALLY know your stuff and it will feel good to have this spot on...

2003 cr 250
Elevation- 995
Whats the correct jetting for this?
Are there any other factors that matter? And at what elevation should I rejet? Like would an elevation of 1200 need a change? Should I find the elevation of all the tracks ill be at this year?
 
Nighthawk016

Nighthawk016

Jhutchh:
I hate to be asking a question that sounds so simple, but I see alot of you guys REALLY know your stuff and it will feel good to have this spot on...

2003 cr 250
Elevation- 995
Whats the correct jetting for this?
Are there any other factors that matter? And at what elevation should I rejet? Like would an elevation of 1200 need a change? Should I find the elevation of all the tracks ill be at this year?
Click to expand...
at 995 above sea level you might need to drop the pilot size 1 and maybe change the clip position on the needle, and 1200 it will most likely be a definitely on both.
 
SRAD97750

SRAD97750

Moderator
Staff member
Jetting is up to feel/plugchop unless you have a dyno handy. Jet it so your plug chop looks good and you like the way it delivers power. Then ride. :ride:

From my riding of large and small displacement motorcycles, 1500ft (change in elevation) can effect a smaller engine, and the bigger displacement engines are effected around 3000ft (change in elevation). Just my 2 cents...
 
Mihylo33

Mihylo33

420 Main 30 pilot 1.5 turns on the airscrew

with a PC pipe they recommend 390 main, 32.5 pilot and 2 turns on the air screw.

this is done with a 32:1 mix ratio with 50/50 mix of race fuel and 92 pump
 
Jhutchh

Jhutchh

Awesome thanks alot.. I've always just jetted to what sounded and ran good.. But I've always wanted to start with 'right' instead of 'what I got' haha
 
Nighthawk016

Nighthawk016

Jhutchh:
Awesome thanks alot.. I've always just jetted to what sounded and ran good.. But I've always wanted to start with 'right' instead of 'what I got' haha
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most of the time you gotta start with what you got. On my 88 I had to start with the jets and needle that came with the bike, 15 pilot 330 main and stock needle, the main was good but the pilot and needle were really rich, now ive leaned both (and put on the proper throttle cable) and it should be relatively close, if not, I still have 1 smaller pilot.
 
PALMER84ONE

PALMER84ONE

Most pipe companies have a jetting/mixture scale that you can look at to determine whats best. You have to remember with a 2T bike it has to do with temperature/humidity (time of the year depending on where you live) in addition to altitude. My YZ250 both have different pipes and different jetting. But because they are both in So. Cal run the same Super pump gas at 32:1 Yamalub R2, and ride the same areas, we never mess with jetting them even between 1500-5500. Yah they run a little rich up there but thats better than lean. Another thing I was taught by the master of the 2T is, never let a 2T idle longer than a minute, minute and half when you walk away from the bike, thats when it is getting the least amount of lubrication in the crank,piston,head, etc... Long lasting motors if you run them on the richer side.
 
Jhutchh

Jhutchh

Well I can't read the inscription on the main at all :( I even used my 5 year olds magnifying glass haha.. The pilots a 32.5 and im assuming the main is stock cause it looks to be the same condition as the pilot..
I think my pilot is plugged beyond cleaning. I've soaked it for an hour, tried shoving a stripped bread tie through it, tried blowing through it, soaked it some more, shook it around in the carb cleaner, I can't see a bit of light through it or blow through it.. I should be able to do both right? Stupid question I know, but I haven't cleaned the carb on this bike yet and its my first 250 so I don't want to guess when I could just ask :P
 
Nighthawk016

Nighthawk016

Jhutchh:
Well I can't read the inscription on the main at all :( I even used my 5 year olds magnifying glass haha.. The pilots a 32.5 and im assuming the main is stock cause it looks to be the same condition as the pilot..
I think my pilot is plugged beyond cleaning. I've soaked it for an hour, tried shoving a stripped bread tie through it, tried blowing through it, soaked it some more, shook it around in the carb cleaner, I can't see a bit of light through it or blow through it.. I should be able to do both right? Stupid question I know, but I haven't cleaned the carb on this bike yet and its my first 250 so I don't want to guess when I could just ask :P
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you could just replace the jets, if the pilot is clogged that bad I'd recommend just replacing it
 
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