Jetting Mikuni TMX Carb on a 2017-2021 KTM 125/150SX and 2021-22 KTM 125XC

[Orange Crush 500]

I have a 2021 KTM 125 SX with a Mikini TMX 38 Carburetor. I ride at Sea level using Amsoil Dominator 32:1 with pump gas.

the 2017-2021 KTM 125/150SX and the 2021-2022 KTM 125XC are all the same.

im curious of what jetting others are running??  whats your jetting/brass and needles your running?

 do you have a JD jetting kit? with what jets/brass and needle?

Whats your Altitude, premix ratio and gas your running?

Im not really interested in a Keihin or a Lectron or a Smart carb at this point.

Thanks

 

Edited July 14, 2022 by Orange Crush 500

[mog]

The 17,18,19 were not similar in jetting....and the 125 runs  different jetting to the 150.

Edited July 14, 2022 by mog

[mlatour]

With the many woes KTM 125 owner's seem to have with the Mikuni TMX38,

I'd be tempted to start with the very best stock settings Yamaha ever had with the same carb on the 2006-10 YZ125 and fine-tune from there.

(later 2011+ YZ125 got a longer silencer, a one-half clip richer needle and, a #430 main jet)

 

sea level, 68°F ambient temp, 30:1 premix

air screw 2-1/4 turns out

# 40 pilot jet

4mm cutaway throttle slide

# 6BFY42-74 needle, clip in 3rd notch

# S-4 needle jet

# 410 main jet

measured fuel level 10mm +/- 0.5mm above the bowl's mating surface (using the clear tube method)

Also making sure the jet block seal isn't damaged.

 

Edited July 14, 2022 by mlatour

[Orange Crush 500]

6 hours ago, mog said:

The 17,18,19 were not similar in jetting....and the 125 runs  different jetting to the 150.

I was talking about the carbs not the jetting. I guess i made it  confusing 

[Orange Crush 500]

4 hours ago, mlatour said:

With the many woes KTM 125 owner's seem to have with the Mikuni TMX38,

I'd be tempted to start with the very best stock settings Yamaha ever had with the same carb on the 2006-10 YZ125 and fine-tune from there.

 

Can someone post these settings?

[Orange Crush 500]

5 hours ago, mlatour said:

 

measured fuel level 10mm +/- 0.5mm above the bowl's mating surface (using the clear tube method)

 

 

Can you explain this clear tube  method?

 

Edited July 15, 2022 by Orange Crush 500

[Orange Crush 500]

5 hours ago, mlatour said:

 

 

Where is this chart from?

[mlatour]

11 hours ago, Orange Crush 500 said:

Where is this chart from?

2010 Yamaha YZ125 factory service manual

Edited July 15, 2022 by mlatour

[mlatour]

The 'clear tube' method is when instead of measuring the float's mechanical height,

it's the actual fuel level that is measured (IMO more accurate, seems only Yamaha specs it this way versus other manufacturers using this carb)

by replacing the drain bowl's plug with one having a nipple and a 12" or so clear length of tubing attached to it.

 

With the carb held/mounted level in a vise, once filled up thru the usual fuel line / inlet spigot,

the level in the clear tube should rise to 10mm above the bowl's mating line (for consistent readings I've found it preferable to 'purge'

the bowl / clear tube of any air bubbles by letting a bit of fuel drain out the clear tubing between each fill/reading)

 

No need to buy the special factory service tool, drilling a spare drain bowl nut, tightly fitting a length of clear tubing into it

plus a small mechanic's ruler held along side with the tubing and carb is all that is needed (also a bit of dexterity and patience never hurts)

Some drill/tap a spigot onto a spare drain plug as per the service tool,

myself just drilled / stuck a tube in it, making sure not too much protrudes inside/touches the main jet.

 

If rather than MX track usage the bike is being mostly being trail/off-road ridden, setting the fuel height about 1.0-1.5mm lower

than the nominal 10mm spec can prevent a lot of fuel loss out of the overflow line on slower off-cambers / hills.

 

Edited July 15, 2022 by mlatour

[Orange Crush 500]

Thanks mlatour

[Orange Crush 500]

Anybody got a JD jetting BLUE needle for my bike. Its in Kit # JDK029..I dont wana buy a whole kit  just for that needle?