PWK 39 set up and jets

[moro241]

Hi guys

I am a newbie in the dirt bike world, and especially in carburetor settings.
I am most certain I have a KEIHIN PWK 39. The problem I have is that most likely I have to rich mix, because despite I use 1:50 fuel mix, my exhaust is filled with black tar substance. I have already changed the exhaust filling, but now I need to set my carburetor right. I have a 180 nozzle in there, so i guess it might be to big, and there is to much fuel getting into to the engine and not all is being used. I have found some post that standart main jet for this carb is max 175. I live in Holland so
I am definetlly under the sea level(as most part of Holland :] ), temps are usually between 10 and 20 celcjus. Thanks for your help in advance.

I ride KTM EXC 300 '97

[dajogejr]

Welcome to the forums, Moro..
I moved your thread to the KTM section where I think you'll get better attention.

Also...as a rule of thumb, do NOT lean your oil to fuel mixture to compensate for rich/lean jetting. Run the premix at the ratio you plan on using.

Here is the proper way to tune your main jet, hope this helps.

http://www.dfn.com/benkaren/plugchop.html

[trblmog]

Good right up on how to jet.
On the tar issue. It could also be the type of pre-mix you are using. What are you mixing with? Don't know what they offer over there but a person who has ben riding/racing for a while has probably been through all the pre-mixes and could tell you which ones leave the worse deposits to which ones smell the best.
Good luck.

[moro241]

OK guys thx for help, that plug chop procedure looks pretty sophisticated :]
But I guess I can try it. I use Castrol Oil to my mix in ratio 1:50 instructions says it should be between 1:40 and 1:60. Another thesis I met was that I didn't put the bike on high RPMs and therefore even when the jetting was right, it didn't burn out completely. Right now I have changed the MJ to 170 and plan to mix a bit more oil with the fuel So the crankshaft will have enough lubrication with slightly smaller amount of fuel . Additionally I secured the ring that the exhaust pipe goes in to, with high temperature silicone, so I supouse that this might help in burning process since there is a part of fumes sucked back in the 2T engine. And get rid off that black tar on the engine block. It is and old bike and I guess previous "owner" didn't took care of it right, but getting all that knowledge while repairing it, is something I find very interesting :]

[JHONNY_ICE_420]

The Black Tar All Over The Block Is Probably Just Exhaust Leaking. Just Get New "o" Rings For The Pipe Where It Meets The Engine