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Jetting issue? Too lean or too rich?

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Hello, i am having what i am almost sure is a jetting or carb issue. Its a 2006 Ktm 125SX with a 38mm keihin carb. I am really having an issue with figuring out if its too lean or rich. I mix 35:1 with AMSoil dominator. Even when i run it extremely hard it still has spooge leaking down my silencer. But it bogs from down low all the way to the powerband than it screams.. Taking off bogs so much.. Not sure what the problem is. Help please?

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Spooge = rich on the pilot or needle and/or clip position. Before you start jetting around a mechanical problem and switching to smaller jets, you would be well-advised to make a few checks. Hopefully your bike and its accessories are relatively stock.

You may have a blocked jet causing the bog. You should be able to see light through the pilot and main jets.

You should clean your airfilter diesel/petrol mixture, or dedicated filter cleaner, rinse and re-oil using filter oil squeezed evenly through the filter in a shopping bag or zip bag and remove extra excess oil.

Next, you need fresh gas, mixed with your oil and correct ratio. Next, you need a fresh plug, with the factory spark plug gap.

Next, take it for a run.

One easy way to eliminate spooge, is to adjust needle clip position higher. It's free and you could try this if the basics didn't help.

If this doesn't work, you need to consider leaner pilot jet, 1 step at a time, while adjusting your airscrew to suit.

I work mainly on Yamahas, so you might be best advised to post over in the KTM model specific section for specific jetting specs.

Good luck.

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Hey Swappa. I'm also having some similar issues with my sons TTR250. It's got a big bore kit in it and the main jet is a 153 and pilot jet is 52 I think, I'd have to remove it again to have a look. I'm having bogging issues right through the throttle range, more so 1/4 to WOT. I think my main jet is too big! I did raise the circlip to the highest setting and got it rideable so now I'm fine tuning the main jets. So I'm wondering if you think I'm on the right track. Spark plug is black by the way.

Cheers.

Dave

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I think you should use 40:1 ratio 35:1 is to much oil i have a 05 125 sx and check your float height my has a little oil coming out of the pipe but it is not dripping on the ground but when my float height was messed up it my bike run bad

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Hey Swappa. I'm also having some similar issues with my sons TTR250. It's got a big bore kit in it and the main jet is a 153 and pilot jet is 52 I think, I'd have to remove it again to have a look. I'm having bogging issues right through the throttle range, more so 1/4 to WOT. I think my main jet is too big! I did raise the circlip to the highest setting and got it rideable so now I'm fine tuning the main jets. So I'm wondering if you think I'm on the right track. Spark plug is black by the way.

Cheers.

Dave

 

Dave,

My nuggett: you may have some water the float bowl which is getting sucked up and blocking your main jet. Remove the drain bolt from the carb, and look carefully for a globule of water.

 

Next, you need to head over the the TTR board and read up as others would have similar experience w big bore kit and pipe (these two typically go hand in hand). http://www.thumpertalk.com/forum/24-ttr/

I know that on YZ 2-strokes, when you go to a big bore kit, they jet them leaner ... I know ... backwards. You might be experiencing the same problem ... You could be richer since the increase in cc's. If you know who the big bore kit is made or sold by (Serco?), you might check their website or go the whole hog and call their US customer support line for jetting specs. These specs should get you in the ballpark only. Note that the TTR is only a trail bike. It shouldn't bog on the trail on on the street, but if you're trying to skim the woops like Chad Reed, you'll probably never cure that hickup.

 

Your big bore supplier/shop should be able to provide this level of backup w some ballpark jetting specs. Best of luck, sorry i couldn't be more help. I raced a TTR in 1999 but it's too long ago now and it was always stock displacement.

 

I think you should use 40:1 ratio 35:1 is to much oil i have a 05 125 sx and check your float height my has a little oil coming out of the pipe but it is not dripping on the ground but when my float height was messed up it my bike run bad

A change in oil ratio won't fix the bog and won't make a noticeable difference in spooge. It's because you're too rich, trust me.  

Edited by Swappa

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Thanks Swappa, it's a 4 stroke, should have said that at the start.... I've put the 137 main jet in to try tomorrow, will report back either way. Ill head over to the TTR section too....

Is it normal to see the header pipe glowing red when running the bike in the shed?

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