New to all this need some advice yz400f

7 replies to this topic
  • jagarcia89

Posted September 14, 2009 - 09:03 PM


Let me start off by saying I haven't been riding my own machine since I rode 80 and 100cc 2 strokes 5 years ago. But I'm long over my broken femur and wanted to get into riding again so I bought a used 400f. I got a lot of questions and anyone that can offer a tad bit of advice would be helpful. Be easy on me, I'm new to four strokes and thumper talk.

First off this bike came from kansas and I'm in CO at 6000 feet, what jets and such do I need to swap?

Also this things a real tough one to start, I can get it eventually but any tips on makin it fire up easier?

And lastly any common problems these things have that i should prepare for or extra parts/ accesories i should look into?

any help is appreciated, even if it's somethin I didnt ask and you got a little tip for these, let me know

  • got5steelman

Posted September 15, 2009 - 07:40 AM


Start off by checking the YZ jetting data base thread in this forum, it is the 2nd post on the front page, you can see what jetting has worked for others, once you get it jetted correctly it will help with your starting issues. I think there is also a link to a video of starting technique in the common thread post also.

  • YZ400dave

Posted September 15, 2009 - 08:22 AM


The 400 is a great bike, but it is 10 years old so you should go in and check your valves and replace your timing chain. while your in there you should think about swaping out the exaust cam with one from a 03 yz450. this will get rid of the decompression lever proceedure and make it easier to start... i did the mod and had never worked on cams or valve and it was pretty easy with the instructions found on here took about 2 hours... adjusting your valves and getting the jetting right will make the 400 an easy starter.. also doing the light blue wire mod found in the sticky will make starting in gear eaiser.. have fun with the 400!

  • jagarcia89

Posted September 15, 2009 - 09:14 AM


Thanks 400dave. and in regards to the jetting thread, I looked at that and no one has jetting posted for a 400 anywhere near 6000 ft

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  • grayracer513

Posted September 15, 2009 - 09:45 AM


Assuming it was correctly jetted for Kansas, reduce the size of the pilot jet and main jet by 5% (multiply the number size of the jet by .95) and start with that.

As to starting, watch:



  • jagarcia89

Posted September 16, 2009 - 10:03 AM


Alright the video definitly helped, I got it to fire up a little easier but I noticed that mine doesn't have the hot start knob next to the choke is the hot start only on 426s, also I noticed that behind the carb near the airbox there is another black knob that says PULL on it, but this doesn't move in or out.

Also when I get it fired up I gotta hold the throttle open a bit for quite a while, then after that it will idle for a little bit then die, could this be due to the carb stuff?

  • grayracer513

Posted September 16, 2009 - 10:40 AM


The knob near the air box is the hot start on a 400. Apparently, yours is stuck.

  • YZ400dave

Posted September 16, 2009 - 05:46 PM


Mine got stuck soon after buying the 400, took it off and disassembled and it was all gunked up with dirt and mud, wd-40'd the s*it out of it and put it back together and it was all good.. dont pull to hard on it though the red knob WILL come off the shaft ... ::busted::

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