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Discussion Starter #1 (Edited)
Hi all does anyone have any working jetting info for my ktm 125 xcw bike has had full ktm/doma factory exhaust fitted

I've done jd jetting jet block gasket

Mukini Carb specs at moment
490 mj
42-73 needle
Clip pos 2
40 pilot
R8 needle jet
1 3/4 turns out on air screw

Blue Power valve spring 2 turns in from fully out

Oil 60-1

Am asking cos I had a piston seizure on a piston with only 6 hour on it

Just replaced barrel and piston just don't want it to happen again after 6 hours

If anyone can help

Just till I have money together to put a keihin on

Thanks in advance
 

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I can’t help on the Mikuni spec but under what circumstances did it seize? Long uphill full load, flat straight, first thing into a ride? Knowing this might help diagnose which area of the take-the-Mik carb is off.
 

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Discussion Starter #4
id been out on bike about 2 hours bike seized when i was wide open in 5th gear level ground

I'll attach pics of piston and plug looks rich to me

Piston looks like a cold seize but I don't get how tho I always let bike warm up before riding
IMG_20200310_161742.jpg
IMG_20200310_161658_1.jpg
IMG_20200310_120534.jpg


IMG_20200310_161742.jpg IMG_20200310_161658_1.jpg IMG_20200310_120534.jpg IMG_20200310_120553.jpg IMG_20200310_120540.jpg IMG_20200310_120603_BURST002.jpg
IMG_20200310_161742.jpg
IMG_20200310_161658_1.jpg
IMG_20200310_120534.jpg
IMG_20200310_120553.jpg
IMG_20200310_120540.jpg
IMG_20200310_120603_BURST002.jpg
 

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Pinders, this is what happened to Dan at ashdown, ktmracing, i cant help you but our mate had same thing piston was fooked like yours...flat out same thing 10 hours or less i seem to rember ?
 

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It’d be the same Tqktm. A seizure is a seizure. Understanding why it happened is key. Dans was to lean on the main for the load. Total bummer.
This one does seem odd. Was it the correct piston size? It does seem odd getting a cold seizure with a richish looking plug but it also depends what part of the jetting was lean if the piston was the correct size. Was there definitely oil in the fuel?
 

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Discussion Starter #8
Am guessing it was the rite size piston shop measured barrel and supplied piston I thought was a bit strange him giving me a size C when I took a size A out

As for the oil I did just change oil brands as shop only had motul In stock mixed at 60/1
 

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Going from an A piston to a C might be the issue then if it were the original cylinder but you said new cylinder as well. Had the cylinder been replated/repaired and that was why the piston was a C?

what’s stock jetting in the manual for the bike? If you have that at the moment then its unlikely jetting is the issue.
 

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Discussion Starter #10
That's what the original barrel was messured to at shop and piston they selected I've now replaced with a new barrel and piston size A

Yes I have manual I've attached photo below of factory jetting specs

I've changed jetting slightly leaner needle and leaner poilt and slightly richer main as it was loading up bad at low throttle input
32561
Screenshot_20200314_090826_com.google.android.apps.docs.jpg



Screenshot_20200314_090826_com.google.android.apps.docs.jpg
 

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Hopefully your issue was the previous piston size and cylinder clearance. Now you have a new cylinder with an A piston it’s unlikely to be wrong. I’ve not had any new KTMs that have come with anything other than an A kit piston.

You are quite a bit leaner on pilot. Plus add in leaner needle and clip setting things could get risky quickly but this depends on how and where you ride. Trickling through flat woods you will probably be fine. Get out onto a muddy or sandy MX track and expect another seize.

I think you’ll struggle to get the Mikuni working well at lower RPM. I’ve messed with several now and there’s always somewhere that you just can’t get right.
 

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Discussion Starter #12
cheers for your input mate what settings would you recommend to try only gonna be for 2 or 3 weeks till i get money together for a keihin carb

thanks again



Hopefully your issue was the previous piston size and cylinder clearance. Now you have a new cylinder with an A piston it’s unlikely to be wrong. I’ve not had any new KTMs that have come with anything other than an A kit piston.

You are quite a bit leaner on pilot. Plus add in leaner needle and clip setting things could get risky quickly but this depends on how and where you ride. Trickling through flat woods you will probably be fine. Get out onto a muddy or sandy MX track and expect another seize.

I think you’ll struggle to get the Mikuni working well at lower RPM. I’ve messed with several now and there’s always somewhere that you just can’t get right.
 
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