Tc 250 carb help

This Mikuni carb is soooo far off from the factory it almost has to be a setup for people to buy the new TPI bikes coming out. It took me a while to get my 300 setup, but the setting from my 300 should be similar to what your bike will need, even for your altitude. My setup is kind of extensive, but addresses a lot of the issues that the stock setup has. This is what I would recommend for your bike.

1--S-4 needle jet---KTM part #---55431021400

2--5.75 slide----http://www.motosport.com/oem-parts/part-number/16022-KZ4-L32?mmysource=… or a #6---http://www.motosport.com/oem-parts/part-number/16025-0004?mmysource=kaw… or if you have the ability cut your current slide into a #6.

3--42-75 needle. Start out in the #3 clip position---------http://www.motosport.com/oem-parts/part-number/284-14116-H5-00?mmysourc…

4- 27.5 pilot jet

5--410 main jet

6---Air screw 1.5 turns out

This a starting point that should get you close, provided that your bike is in good working condition. Have you checked the reeds yet ?

The reeds should be sealed tightly against the reed block. Shine a light into the back side of the reed block, in a reasonably dark room, and look for light coming thru gaps against the reed block. there should be very little that makes its way through. If there are large enough gaps it can cause problems with way the bike runs along with jetting issues.

http://m.vitalmx.com/forums/Tech-Help-Race-Shop,42/2017-KTM-250SX-Carb,…

There are several threads on here about jetting these. In a nutshell, it's rich from the factory at sea level so isn't going to be much better at elevation.

I would start with a 27.5 pilot jet.

Check your reeds, if you look thru it towards light and it's coming on the edges the cage or pedals might be warped. This was mine on my 16 125. I was chasing jetting then figured this out.

Does the 60:1 ratio recommended by the factory and verified by MXA on the stock carb actually work? How much does this ratio shorten engine life ?

Motul 800 hast a very high flashpoint. Maybe try a different oil with lower flashpoint to get a cleaner burn.

My suggestion is to buy a JD Jetting kit and a set of VForce reeds. My TX300 ran like shit with stock jetting and with the suggested jetting for my atmospheric conditions. My reeds also had gaps.

I installed a JD jetting kit and VF4 reeds. Bingo. Runs crisp, no flat spots anywhere in the RPM range. I'm running 50:1 Amsoil Dominator. If you run the same mixture ratios you would run in a 125 (like 32:1), you're never going to get the jetting right, it will foul plugs and spooge like a 12 year old with the JC Penny Valentine's day catalogue.

I'm running a 410 main, 32.5 pilot, AS somewhere around 1.5 and the blue JD needle on the 3rd clip.

I run 32:1 in my TC250 with 93 octane. No spooge.

Excerpt from my post linked above:

I did have the issue with the reeds and sanded the block so they would sit mostly flat. I think there was a small gap left from one reed being slightly conformed to the warped block.

I also adjusted float to recommended height (~8.5 - 9 mm I think).

Bike ran pretty good with 450 main, 35 pilot, stock needle, 3rd clip.

I then had 0.020" taken from cylinder head face and ran 430 main, 32.5 pilot, and stock needle 2nd clip. Had some very minor pinging at a particular rpm/throttle position.

I installed the JD Jet kit blue needle on 4th clip, along with a 30 pilot jet and AS at ~2.5 turns out, and now it runs better than ever. I was very skeptical of the JD Jetting kit, but it is actually better. Maybe not $70 better, but over the life of the bike it's probably worth it. BTW, I'm running 93 octane at 32:1.