YZ426F Blocked Pilot Circut or Valve issue

Discussion in 'Thumpers' started by foreverboard, Mar 28, 2016.

  1. foreverboard

    foreverboard Adventurer

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    Whistler bc
    Hey guys, I bought a 2002 YZ426F this winter with the hopes of bringing it back to life from the previous owner not giving it the love it needs. When I got the bike it wouldn't run so I dove into the carb and cleaned it and still nothing. I went into the top end and shimmed the intake valves into spec because they were quite out of wack and it would run but the second I released the choke it would die. I pulled the carb off looking for the pilot jet to be blocked but it was fine. I've looked for vacuum leaks around the boots but it's hard to tell when it's running on the choke. I took a few pics... one of the intake and exhaust valve buckets and the exhaust bucket (right side ) seems to be sitting in oil is this normal. Another thing I've read is if you do not align your Cams up properly it can cause it to not idle so I took a picture but it looks good to me. One other thing to note is the Carb float bowl gasket looks a little worn. Could this cause enough of a vacuum leak to make the bike not idle? I'm trying to figure this out on my own but ive hit a road block but dont want to give up. Any advise you could give me would be awesome and hopefully it's something small I am over looking

    Thanks for reading 20160328_100428.jpg 20160328_095321.jpg 20160328_100428.jpg 20160328_100428.jpg
    #1
  2. Snks

    Snks Been here awhile

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    Feb 4, 2014
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    557
    Pilot jet could be partially plugged. I would replace the pilot jet they are hard to clean. Also make sure the port above the jet is clean.
    #2
  3. debaisley

    debaisley Long timer

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    Timing is good , there is no auto decompression on that bike so should be easy to check if its getting good compression.
    #3
  4. SpaceCowboy7777

    SpaceCowboy7777 Adventurer

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    if the bike isn't fully warmed up, it won't idle without the choke. Also your idle could be set too low, try turning it up.

    I'd recommend buying the jd jetting kit and an easily adjustable fuel screw, my wr400 runs better than ever with those. Best $100 I've spent on the bike
    #4
  5. foreverboard

    foreverboard Adventurer

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    Hey guys,

    The pilot is new so should be all good there but I'm not sure about the circut itself. Carb cleaner will come through the fuel screw hole but not the pilot air jet

    The compression feels ok but I haven't checked it.

    I'll try giving it a solid warm up before I run it next time and I'm pretty sure the idea is in a goof spot. To me it seems like the pilot circut isn't getting fuel because it dies so quickly after the choke button goes back in. Did you guys see the one picture with the exhaust valve bucket in a puddle of oil? Is that normal? It's the only one that has that much oil around it.
    #5
  6. Indy Unlimited

    Indy Unlimited Long timer

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    Location:
    Parker, CO
    Definitely sounds like carb issues. I would check all the vent tubes make sure they are clean and clear. adjust your idle high while running with the choke to get her to run without the choke. Check the carb slide is not installed upside down.
    Pilot air jet needs to be clear and good idea to take carb off again and clean the entire carb with cleaner thoroughly. You really need to check the fuel screw is out 2 turns and the washer 0-ring and spring is intact.
    Jetting: start with this: 165 main jet, needle in middle clip position, and 42 pilot jet, fuel screw 2 turns out.
    There are a lot of seals and rubber parts in the FCR carb.
    Sudco sells all the parts you need to replace all seals and o-rings:

    http://www.sudco.com/images/FCRMX.gif
    #6
  7. debaisley

    debaisley Long timer

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    #7
  8. davesupreme

    davesupreme grand poobah

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    i didn't have the problem you're having, but.... i just changed that big o-ring thing that fits between the slide and that plate on the front of it... you can see it in the fiche.... made a BIG difference... that big oring thing seals it all up so you have good vacuum... check it out... should fit to the throttle plate pretty tight, my old one was pretty soft and loose....
    #8
  9. foreverboard

    foreverboard Adventurer

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    Thanks for all the info guys. I pulled the carb apart and noticed all the gaskets are pretty flush with the metal. Would this cause enough of a vacuum leak to cause my issue. Also I noticed there is a piece of the neck missing where the pilot jet screws in. Not sure if this would cause anything either.

    The carb is all clean and jets are good to go. I noticed the main was a 162 so I stuck a 165 as Indy unlimited recommended. Also the fuel screw o-ring felt a little worn so put a new one on. Hopefully this sorts it out but if not I guess a gasket kit is next. I will report back with what happens

    Attached Files:

    #9