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Ktm 300 jetting issue

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Hy. Just finished build my top and bottom end and i can t get my jetting right. At about 1/2 throttle it feels like it s to rich mixture but after  that it revs really good. My pilot is 35  , main 165  , needle N2ZJ, 2nd clip from top. Tried in 1st clip position but it seems it revs to quickly and sounds thin. The spark plug is black even in 1st clip position.

Edited by avliviu

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The plug is dry black or wet black?

 

Revving quickly and sounding thin indicates lean to me.

 

Was the jetting ok before the rebuild?

 

What's your elevation?

 

I too had trouble dialing in the transitions between fuel circuits with the stock dual taper needles. I put in a Suzuki triple taper needle.

 

If the N2ZJ is indeed too rich at the 2nd from top position, have you tried the stock N2ZK needle at 2nd from top? It will be 1/2 clip position leaner than the J at 2nd from top instead a full clip position like it was when moving it from 2nd to 1st.

 

Or try coming down 1 size on the main jet with the J needle 2nd from top.

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on 1st clip was dry black and on 2nd clip somehow wet.100 m is the elevation. i also knew rev and sound indicates lean but the plug was black which indicates rich. The bike had never been jetted perfect but i thought it was from the engine. also it was jetted with pilot 48 pilot and 178 main. The needle i dont remember.

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on 1st clip was dry black and on 2nd clip somehow wet.100 m is the elevation. i also knew rev and sound indicates lean but the plug was black which indicates rich. The bike had never been jetted perfect but i thought it was from the engine. also it was jetted with pilot 48 pilot and 178 main. The needle i dont remember.

Why did u go from 48 to 35? I've never heard of someone running a pilot that small...

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it was not idling ok and below 1/2 throttle it felt very (i don t know how to say) vibrating .it felt like it was very rich mixture and the engine did not pull. the bike was bought from italy and i think it was riding at very high altitude with that settings.

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it was not idling ok and below 1/2 throttle it felt very (i don t know how to say) vibrating .it felt like it was very rich mixture and the engine did not pull. the bike was bought from italy and i think it was riding at very high altitude with that settings.

That's a big jump... Try 40 0r 42 pilot.

You should only change 1 thing at a time to see how it reacts otherwise you'll never know what's happening in there.

Your jetting settings should be richer the lower the elevation.

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Get the Suzuki necj needle to clean up your bottom end. I could never get the factory needles to run right.

Correction: The pilot and plastic idle screw affects idling.

I don't have a 300 so I can't comment on specific sizes.

Your plug color depends on how you shut the engine off. A rich needle will blacken the plug after idle.

For instance here's how to test a main jet:

" Use a fresh plug or one that has only a few passes on it. This works best in top gear or an upper gear on a slight uphill area. After running the engine at full throttle for about 8 to 10 seconds ( do not run up on the rev limiter as this will give a false reading of the plugs) do the following at the same time: pull in the clutch and stop the engine. DO NOT let the engine idle and DO NOT let the clutch out until the vehicle has come to a stop. Remove the spark plug and examine the INSULATOR (the porcelain) color. White is lean and black is rich. Best color is a tan to grayish-white. White means main jet is too small (lean) and black means main jet is too big (rich).

Use common sense and don't do this if it is unsafe."

P.s. Your jetting specs may be different than those of Americans being that your pump gas is 93 I think. The best way to jet is to test test test on your own.

You'll know when you get it right these engines really open up

Edited by Casing-daily

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But the pilot does' not  affect idling and 1/4 trotthle?

 

Yes, the pilot and air screw DO effect idle and off idle, but by 1/4 throttle their effects have tapered off and you're well into the effect of the starting taper of the needle.

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google spankys jetting guide on how to set air screw

 

i would say you will find a 40-42 pilot would be good (some run a 38 , never seen a 35 used)

with the needle i would probably go with a NEDJ which is 1/2 clip richer then a NECJ and run in second clip(which is equivalent to 2 1/2 clip position NECJ)

reason being if bigger bore bikes can be run leaner

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On 300's I believe most people use 38/40 primary jets and 165-170 main jet combos. Some use other combinations depending on atmospheric conditions and personal preference, but these appear to be the most common jets.

Edited by Cuda7050

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On 300's I believe most people use 38/40 primary jets and 165-170 main jet combos. Some use other combinations depending on atmospheric conditions and personal preference, but these appear to be the most common jets.

you can run leaner main jets with a NECJ , a 165 would be a good starting point

my guess is you might end up at a 162

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So after a long wait for the jets i finally got them. 38 pilot and 168 main. The bike feels different. only thing i don't like is that when i m not on the gas and suddenly open the trothle i have a delay. it still feels  richer (about half throtle ). After this runs smooth. If i m all the time on gas it revs with no problems , much better than before. Needle is NECJ 2nd position from top. air screw 1 3/4 turns.

Edited by avliviu

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Before you do anything else, please check to see that the power valve is hooked up correctly and working..   

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Next thing is the muffler or silencer.  If it is clogged or restricted your  engine will not rev correctly..    Easist way to check is to remove it and ride it a bit..  

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So after a long wait for the jets i finally got them. 38 pilot and 168 main. The bike feels different. only thing i don't like is that when i m not on the gas and suddenly open the trothle i have a delay. it still feels richer (about half throtle ). After this runs smooth. If i m all the time on gas it revs with no problems , much better than before. Needle is NECJ 2nd position from top. air screw 1 3/4 turns.

My kx does the same thing at 1 3/4 turns out and gets better at 1 1/4 , long story short as someone just stated its just a lean coming on the throttle, if you get to 1 turn out or less , switch to a 40 or 42 pilot , your almost there just a bit of fine tuning needed

Edited by kxrob

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