mike-evans

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Sep 16, 2009
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2006 KTM 125sx, fitted my Doma system and first ride out today..

Run it on standard jetting, and although there was alot more power, I was a little paranoid it may be lean. So I raised the needle by 1. I cant be certain if it made it better or worse lol...

While holding it on the band, the letting off and back on the throttle, I think Ive got a slight bog/miss..

Below is a pic of how my plug looks.....

I think it looks good, but after fitting the Doma, Im consious of it being lean...

Ive read stickys, and jetting links for a while now, but anyone got experience of how a lean 125sx feels?

The bike could well be running perfect, but Im just worried of any lean condition from fitting the Doma system.
 

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Rich Rohrich

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That picture doesn't show very much but the plug looks fouled or at least carboned up enough to not tell you much of anything useful.

There are some decent plug pictures in the following thread that will give you a better idea of what a two-stroke 125 plug should look like.

http://www.dirtrider.net/forums3/showthread.php?t=92818&page=1&pp=10
 

mike-evans

Member
Sep 16, 2009
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Ok thanks :)

Ive read the posts in the link, and what Im gathering is the base of the insulator is where I need to be focusing...

But I have one question. When fitting aftermarket exhaust systems to a 2 stroke, does it make the whole carburettor circuits leaner? Or just 1 circuit?

I will admit that Im never WOT. At most 1/2-3/4 throttle and in the power band...

The plug was taken out after a few seconds of, 2nd then 3rd then 4th power band at probably 1/2-3/4 throttle....
 

Rich Rohrich

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mike-evans said:
But I have one question. When fitting aftermarket exhaust systems to a 2 stroke, does it make the whole carburettor circuits leaner? Or just 1 circuit?

There are too many variables to be able to answer that with any degree of accuracy. You just have to test after you change the pipe, no real way to get around that.

A lot of people use the "The Ride and Feel Method" of jetting if they aren't comfortable with plug reading.

Eric Gorr wrote a great article explaining it in detail :

http://www.chicagostories.net/ericgorr/EG_Carb Tuning.html
 

mike-evans

Member
Sep 16, 2009
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I'll drop the needle clip back to standard when I'm out next and see how it feels..

When the bike has a bog/miss/splutter etc...... how do you determine if its a lean issue or a rich issue?
 

Rich Rohrich

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mike-evans said:
When the bike has a bog/miss/splutter etc...... how do you determine if its a lean issue or a rich issue?

Experience mostly.
 

Rich Rohrich

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mike-evans said:
Ok I rephrase... how do "I" determine the difference between a rich and a lean bog? Is there any obvious difference?

Honestly, the best way I know of is to force the condition on a safe circuit (like the pilot circuit) so you get a feel for the difference. Go way rich from a know close starting point, and then try going way lean so you can feel and hear the difference. If you use the pilot circuit you can't hurt the engine but you can learn a lot in short order, and what you learn can be applied to the other carb circuits.

The difference between rich and lean by feel and sound is tough to put into words, but is fairly easy to understand when you do some simple experimentation .

Give it a try!
 

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