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KTM 300 exc 2004 - new to me.... Jetting needs attention

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I have done only a little 2-stroke jetting in the past, so just wanted a bit of advice before changing too much.

 

I'm near sea level +100m, east coast NSW Australia.

 

Bike starts very easily... no choke required

 

When cruising 1/4 throttle it is very sputtery

Mid range is pretty strong

Top end very sputtery

 

The air screw doesn't seem to have much affect, went from 1 turn to 2 turns out and no change in idle.

Idle screw is 3/4 of the way in. Is their an air passage that could be blocked making the air screw ineffective?

 

All of this tells me too rich, but would it just be pilot circuit, or needle too since top end was rough?

I'm going to pull it out and check it over tonight.

I'll post jetting and see if it is right.

 

I'm just a little paranoid about leaning it too much.

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Don't know needle. Couldn't find a socket small enough. But it has a bit of wear and am guessing stock.

Main 162 ( stock )

Pilot 40 ( manual says 35 )

Gave it a going over and blew some air through it all.

I'll keep backing air screw out to see if it changes anything.

Try a quick run tomorrow.

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If you haven't installed a new spark plug yet, do that. Don't try to make and gage jetting changes on an unknown plug condition.

 

The air screw is already fully open at 3 turns out, so don't go more than that.

 

With the bike being new to you, it would certainly be in your best interest to remove the carb for a full cleaning.

 

Be sure the reeds are in good shape. No amount of jetting tuning is going to help if the reeds are shot.

 

Tune the air screw using the "whack the throttle" method.

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Has a brand new plug and I found a 160 main and a 38 pilot in my junk. Raining here just now so can't test. Just starting already shows difference though. Actual needed choke from cold. Was definitely way too rich before.

Edited by Thommo_400f

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So... 160 main and 38 pilot.

Still stumbly.

Stock needle setting per manual is clip 1. It was on 3. So I will drop it back to 1 and start testing again.

I have ordered a 35 pilot so might have to put up with a slightly rich bottom end until then.

Edited by Thommo_400f

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Ok, so the needle was 2 steps richer than stock setting. The needle position has an effect just off idle, so you should definitely see a difference dropping it 2 positions.

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Funny what people do for no reason. The carb is in good condition and there is heaps of compression. I'm a bit stumped why previous owner had it jetted so rich. Was terrible to ride.

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Ok ... Dropped needle to #1

Reset air screw to 1.5

Pilot 38

Main 160

Way better than before!

Only a bit to go... I think a 35 pilot will fix it.

Once my 35 is tested I might try the 162 main again. Seemed like it died off a bit early in top end.

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Temps at moment are around 19-25c during the day. I'll try air screw adjustments now since it's getting close to good. Air screw is tight to move since previous owner must have used a screwdriver too big and damaged threads :/

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No two bikes are the same, but I am currently running 35 pilot, NEDJ needle, 3rd clip, and 165 main. Just for reference purposes... definitely not saying you should blindly follow my jet specs. Also, mine is an 05.

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Thanks

My philosophy has always been never stray too far from stock (apart from altitude/temp adjustment). Bike manufacturers know what works. Big changes in jetting will almost always be a symptom of another issue. I'm almost back to stock and the bike is running better and better :)

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