My yz426 is running too lean



7 replies to this topic
  • Riley_christensen

Posted November 12, 2015 - 09:06 PM

#1

How do I adjust how lean or rich my 426 is running, I just got the bike and the guy said it sat for awhile and we started it and it died right when he started it a few times and after a few min of idling the manifold started glowing hot red. I've never had this issue with my yz250f and don't don't how to adjust it. Any help?

  • Dirtrider 88

Posted November 12, 2015 - 09:37 PM

#2

Wow. If you have no clue take it to a local Yamaha dealer. They will be able to rejet the carburator and hopefully that will make it stop. Some people run the bike so lean that to keep it running you must constantly rev it. Because the more lean it is the higher it will rev. I don't think that's the case here though. Sounds like you got a sleeper of a bike that needs a bit of TLC to run correctly

  • Riley_christensen

Posted November 12, 2015 - 09:42 PM

#3

I was told to maybe clean the carb and then adjust it but idk how to adjust it to the proper settings! That's what I'm trying to figure out

  • Krannie McKranface

Posted November 13, 2015 - 05:48 AM

#4

How do I adjust how lean or rich my 426 is running, I just got the bike and the guy said it sat for awhile and we started it and it died right when he started it a few times and after a few min of idling the manifold started glowing hot red. I've never had this issue with my yz250f and don't don't how to adjust it. Any help?

 

A glowing header is normal if you let it sit idling. 

 

If it won't idle even after adjusting the idle screw, you probably have a compromised pilot jet circuit, which is typically just a corroded or blocked pilot jet.

 

Until you service the carb completely, there is no point in assuming the jetting is off, even if it is.

Do a valve clearance adjustment too.

 

http://www.dirtrider...r_carb_rebuild/

 

This indludes replacing the wear items (assuming it has some real hours on it) like the needle jet, slide plate seal, and apump diaphragm.

You also need an aftermarket fuel screw for easier adjusting. (R&D racing).

 

While the carb is apart, you need to verify the previous owners jetting, and veriry the apump is squirting.

You can read the FAQ's or Jetting thread to find your bike, and copy someone else's jetting, if needed.



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  • Dirtrider 88

Posted November 13, 2015 - 08:03 AM

#5

What @krannie said is very correct. My o9 yz250f header glowed if it ran for more than 5 minutes at idle. Best to kill the bike if your gonna sit for more than a minute or 2

  • grayracer513

Posted November 13, 2015 - 08:38 AM

#6

... the more lean it is the higher it will rev.

 

 

Sorry, that's false.

 

You said the bike is hard to start and doesn't like to idle, and that it sat a while.  A common occurance is for the pilot jet, which controls idling and most of starting, to develop a film of dried fuel varnish that reduces its size.  The metering orifice in these jets is very small, so it only takes a thin film to make a difference. 

 

Start with a free manual download:

http://api.viglink.c...uals/index.aspx

 

http://api.viglink.c...ook.com.au/?r=0

 

Then read about cleaning the carb:

http://www.thumperta...o/#entry6879695

 

Then follow the procedure in the manual for adjusting the idle.  If you don't get any results from that adjustment, it usually means you missed something in the carb, or there might be a valve clearance or timing problem.

 

It is normal and mostly harmless (as long as you stay clear of it) for the header to glow red enough to be seen in the shade of a garage, or at twilight if you let the bike idle for as much as a minute, but it's also true that a lean and/or fast idle will make that worse. 



  • Dirtrider 88

Posted November 13, 2015 - 08:49 AM

#7

Sorry, that's false.

You said the bike is hard to start and doesn't like to idle, and that it sat a while. A common occurance is for the pilot jet, which controls idling and most of starting, to develop a film of dried fuel varnish that reduces its size. The metering orifice in these jets is very small, so it only takes a thin film to make a difference.

Start with a free manual download:
http://api.viglink.c...uals/index.aspx

http://api.viglink.c...ook.com.au/?r=0

Then read about cleaning the carb:
http://www.thumperta...o/#entry6879695

Then follow the procedure in the manual for adjusting the idle. If you don't get any results from that adjustment, it usually means you missed something in the carb, or there might be a valve clearance or timing problem.

It is normal and mostly harmless (as long as you stay clear of it) for the header to glow red enough to be seen in the shade of a garage, or at twilight if you let the bike idle for as much as a minute, but it's also true that a lean and/or fast idle will make that worse.

okay buddy thanks for pointing that out. I don't know the whole thing about motors. It just worked on nitro rc cars lol. But thanks for pointing it out

  • grayracer513

Posted November 13, 2015 - 10:20 AM

#8

RC car engines are generally all two-strokes, for one thing, and nitro behaves in a vastly different manner than gasoline does.







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