Carb/jetting help?

Iceman said:
Ok for the 08 50jr sx, lightly turn the air mixture screw ( small flathead closest to the airbox) all the way in ( lightly seated, don't tighten it down, it'll damage the needle) then back it out 3.5 full turns. This is factory setting. Fire it up, adjust the idle speed via the idle speed screw ( larger thumbscrew in the centre of the carb body) just adjust to a good idle speed, no specific setting. Take it for a rip, check plug colour, you can adjust for a rich/lean condition with the smaller air mixture screw tha you earlier set to. 3.5 out. Then readjust the idle speed as needed. Small 1/4 turns only with the air mixture screw, then try it. A little spooge (oil residue) from the exhaust is ok. You want a clean, snappy throttle.
The 50 mini is the same process except that as far as I can tell , there is no air mixture screw. Simply adjust idle speed via the throttle stop screw ( again, the large thumbscrew in the center or the carb body.
Ktmdirtquestions.com. Great site, online manuals etc. thumpertalk.com an off-roaders best friend
Hope it helps. Good luck to the little guys, hope they have a lot of fun this season.


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there is one on the mini too, i played with it i know lol. That was good advice though and will definately try that! The other thing I have to read up on with the sx jr is the clutch stacks. I want it to hit harder...doesnt really kick in till it really gets up to revs.
 
How did you determine it was running lean?

Don't worry, you'll have plenty of time learning how to do maintenance on the clutches. Find a ktm 50 forum.
 
dricked said:
How did you determine it was running lean?

Don't worry, you'll have plenty of time learning how to do maintenance on the clutches. Find a ktm 50 forum.
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i found them....many of them! lol
 
The idle screw and the idle jet adjustment will have very little affect on the overall running of the bike as they only control approx the first 1/8 of throttle opening.
 
Tripletrouble said:
The idle screw and the idle jet adjustment will have very little affect on the overall running of the bike as they only control approx the first 1/8 of throttle opening.
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This is true, however those 2 screws are all that we're touched. The bike runs good, he just screwed with idle, just giving baselines to get the idle crisp/clean. I don't believe Ajaxguy pulled the carbs or changed any jets.


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So again, how was it figured to be running lean in order for it to be assumed anything needed to be adjusted other than the idle screw?
 
You can tell if the bike is running lean by checking the spark plug after the bike has idled. This is the best sure shot way to determine

Also you can hear the exhaust sound more "pop corny". You need to know your bike real well to do this method
 
cbcanada said:
You can tell if the bike is running lean by checking the spark plug after the bike has idled. This is the best sure shot way to determine

Also you can hear the exhaust sound more "pop corny". You need to know your bike real well to do this method
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Negative ghost rider, a two stoke race bike idling will have black plugs when pulled or foul after a short amount of time, that's why they constantly blip the throttle. Checking this way only tells you wether your running rich or lean at idle. This is why I ask because if you just assume the bike is running lean you screw **** up and chase your tail. Assume it's rich and you blow **** up but whatever.

I have no experience on a ktm 50 which has a magical carb that can only be adjusted by those with ktm 50's lol.
 
dricked said:
Negative ghost rider, a two stoke race bike idling will have black plugs when pulled or foul after a short amount of time, that's why they constantly blip the throttle. Checking this way only tells you wether your running rich or lean at idle. This is why I ask because if you just assume the bike is running lean you screw **** up and chase your tail. Assume it's rich and you blow **** up but whatever.

I have no experience on a ktm 50 which has a magical carb that can only be adjusted by those with ktm 50's lol.
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Yes i was only trying to determine if its running lean at idle

The the second test would be to ride bike open throttle and pull clutch in and hit kill switch. And check plugs again
 
Yep, so it's impossible to help until we know how this has been diagnosed. It's probably running fine and the idle just needed to be adjusted. Over complicating just makes more work and useless posts.
 
Just to play devils advocate here dont jet anything right now. Too cold yet. Once it warms up your perfect jetting will be too rich.
Wait until the temp is closer to 90% of your riding season and do it then or get it done on a dyno where temps can be controlled. Back in the day we would change jetting from morning to afternoon as it warmed up. Modern CV carbs will allow some play but it is limited.
 
kneedragger88 said:
Just to play devils advocate here dont jet anything right now. Too cold yet. Once it warms up your perfect jetting will be too rich.
Wait until the temp is closer to 90% of your riding season and do it then or get it done on a dyno where temps can be controlled. Back in the day we would change jetting from morning to afternoon as it warmed up. Modern CV carbs will allow some play but it is limited.
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^^^

Rock solid advice right there. Also consider oil/fuel mixture when discussing 'lean' on a 2 stroke engine. More oil will reduce the amount of fuel in the fuel / air ratio.
 
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