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Part 1 of 3 videos on how to jet your 2 stroke MX dirt bike. This part covers the introduction of the Keihin PWK38 carb. common on the Yamaha YZ125, YZ250, KTM 250SX, 300SX, 125SX, Some of the later KX250 and RM250, and some I'm missing. Enjoy!
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Thanks for watching!
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[@danieldemayo6209]

Thanks for this. Carbs/Jetting has be something I’ve avoided for years lol

[@UpAllNight91]

Right on! Hope it was of help.

[@chadrides914]

Good stuff. No matter how much I know about Keihins I still enjoy listening other people’s thoughts on tuning them. Nice work.

[@UpAllNight91]

Thanks!

[@askmeyicare]

Most informative MX videos on KZbin! I’ve learned so much thank you. Can’t wait for the next one!

[@UpAllNight91]

Thanks!

[@rcuniversespeed9447]

Great video. Can’t wait for next one!!!

[@forrestcoleman2659]

This is a spectacular video!!! Thank you so much

[@UpAllNight91]

Thanks! Glad to hear it helps!

[@grubbm4927]

Great video! Looking forward to parts 2 and 3!!

[@UpAllNight91]

Thanks! Hoping to have 2 out mid week this week.

[@thomasphilyaw8593]

Looking to buy one here shortly. Thanks for the great tutorial. Can't wait for part 3

[@UpAllNight91]

Nice! Thanks and thanks for watching!

[@chadrides914]

Good job and explanation on float bowl height at 16:00 👍

[@UpAllNight91]

Thanks!

[@barkeep25]

Quick tip if you got an overflowing carb after putting back together. Shut off gas and blow in to the gas line, hard n fast. it'll reset the float valve. Usually works

[@UpAllNight91]

Yes. That does work too. Done that before. But be careful on some carbs like the KTM85 and ltz400 carbs have rubber o rings around the removable float needle seat. I have blown them o rings out by blowing air into the fuel inlet

[@cemooregreen7512]

99s don’t have the pwk I believe they ran the pwm until 03 on those the idle control is integrated into the choke which I see a lot of people mistake and said the air screw is the idle adjustment, just for anyone with older bikes in the comments screwing the choke counterclockwise will open air flow and clockwise will close.

[@UpAllNight91]

I think you are correct. At least for 1999. I thought by 2000 they where all PWK but could be wrong.

[@keithalexander36]

lube the boot slightly before lowering subframe and boot will slip over carb super easy.

[@UpAllNight91]

Thought it already had enough 2 cycle oil on it lol. Usually goes on easier than that though

[@loganhamilton245]

Awesome videos man appreciate the effort! Hey have you ever encountered a fuel starvation problem at WOT?

[@UpAllNight91]

Thanks. Yeah I have, from clogged petcock.

[@bradleymuha4861]

you really know your shit! Glad I found your channel I can learn a lot from you!!! What year is this 250cc? Clean bike thank you for the great information!

[@UpAllNight91]

Thanks, appreciate it! she's a 2018. About 160 hours on her now.

[@alexistrate8025]

Hey. Can you give me a hint of how i could set my idleing plastic screw to neutral position ? ( Not air screw ) if i cant find a good neutral position is hard to determine the right jetting and corect position of the air screw. The idling a screw play a huge role and cand dump a tone of air inside.

[@UpAllNight91]

They can be very touchy. I usually set mine where it barely stays alive. It idles just high enough to barely keep it alive if I need to adjust my Google or whatever. Being these are race bike they are not really the best at getting a good trail bike like idle.

[@joebortmas6593]

Hey man, great video! I have an 04 yz250, it's pouring gas out of the side hoses. I rebuilt it, put a new needle valve in, the seat looks fine and the float height looks fine.. I can't figure it out.. any ideas??

[@UpAllNight91]

Hello. Sometime that can happen when the needle doesnt seat in well. Try this... Turn the gas on to fill the bowl then shut the gas off. Start the bike and let it run with the gas off for about 1 to 2 minutes. Then turn the gas back on while its running. let me know if that helps, if not we can go to step two lol

[@whiteman3075]

Air screw is intake side of carb and fuel screws are exit side or engine side. Some two stroke carbs have both. Don’t think Iv ever seen an air screw on a four stroke.

[@UpAllNight91]

Ahh, never actually notice that. Totally makes sense.

[@traviskinman3459]

Long time viewer first time asking a question. I have a 86 yz250 with a mikuni that has a #350 main and I'm replacing it with a newer pwk but it has a 150 main. Is this not going to work?

[@UpAllNight91]

Hello., thanks for watching and good to hear from ya! Hmm. 150 sounds a little lean for a YZ250. I mean it might be ok but hard to say. If I was putting a PWK on a 86 YZ250 I would look at what jetting the earlier YZ250 came with that had a PWK on it. I checked pro circuits site to see what jetting the 1996 to 1998 YZ250 came with (here is a link www.procircuit.com/jettingspecs6.htm ) and I would start with that jetting and then make changes from there. The 1996 to 98 YZ250 had the same bore and stroke as the 1986 so its a good place to start.

[@Liliros]

Hello, I have mounted a fatty and shorty fmf exhaust on my yz 250 23, my question is is it protected with the 50 n3ew pos 2 series carburetion and 178 main jet, or should it go up to 180, thanks in advance

[@UpAllNight91]

Hello. Near sea level that will be good safe jetting. Air screw around 1 turn is good too. I would try a 52 pilot, sounds rich I know but this motor likes it at tip in. And a 175 main might wake that FMF pipe up. Would try that too.

[@Liliros]

@@UpAllNight91 thank you so much

[@UpAllNight91]

@@Liliros No problem!

[@nastysoda9212]

I love you