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Thread: 84 250r running lean

  1. #1
    Join Date
    Mar 2020
    Location
    Rhinelander
    --
    5

    84 250r running lean

    So I have a 84 250r and I just rebuilt the top end now it leans out when I’m running wide open. The motor revs itself so I have to use the brake to bring it back down to idle. My question is if it didn’t do it before the rebuild it shouldn’t be crank seals right? Would you guys just think it’s main jet? It idles good and plug is dark brown. Just want to know where you guys would start? I will pull stator cover tomorrow to see if there is any oil residue and it doesn’t smoke like it would if the clutch side were bad.

  2. #2
    Join Date
    Mar 2020
    Location
    Georgia
    --
    48
    Check your float level before you start messing with jets there is a lot of things that will make your engine lean. Another thing is rev it up at idle if it goes back slowly then you will need to turn your screw that moves the slide up and down bring out Iíve had that problem before I done that and that fixed it but it wonít idle so it could be that and the float but try the screw trick first before you tear your carb apart.

  3. #3
    Join Date
    Mar 2020
    Location
    Rhinelander
    --
    5
    It doesn’t have an inline filter so it’s very possible that it got something in the carb. I will clean the carb tomorrow also and take notes of jet sizes just in case it still does it. I don’t want to run it much in fear of blowing it up. lol

  4. #4
    Join Date
    Mar 2020
    Location
    Georgia
    --
    48
    Yeah I would be careful about it running lean especially since it’s a 2 stroke. And yes look into the air filter cause that would open up more air into the engine.

  5. #5
    Join Date
    Mar 2020
    Location
    Rhinelander
    --
    5
    I meant inline fuel filter and I plan on changing air filter too.

  6. #6
    Join Date
    Mar 2010
    Location
    Slidell, LA
    --
    4,625
    Quote Originally Posted by BrandonRadtke View Post
    So I have a 84 250r and I just rebuilt the top end now it leans out when I’m running wide open. The motor revs itself so I have to use the brake to bring it back down to idle. My question is if it didn’t do it before the rebuild it shouldn’t be crank seals right? Would you guys just think it’s main jet? It idles good and plug is dark brown. Just want to know where you guys would start? I will pull stator cover tomorrow to see if there is any oil residue and it doesn’t smoke like it would if the clutch side were bad.
    I don't know what you mean by "motor rev's itself".....

    If you just rebuilt the top end but didn't pressure test the motor post rebuild, you have done yourself a disservice. I would start by pressure testing the motor (this is not a leak down test, this is a crank case pressure test). There are many how-to articles, a few I have written myself on the subject that you can find on this site.

    A dark brown plug after idling and riding will tell you nothing. The plug could be brown from the idle circuit or the needle circuit or the main circuit. Once you have the motor pressure tested and it passed (needs to at least hold 6lbs for 6minutes) then move on to the carb. A thorough cleaning would help along with identifying the jets you are currently running. On idle circuit your air screw should be turned out 1.5 turns and your engine should rev fast and then quickly come back to idle. If this is not the case then your pilot is wrong.

    Start on the pressure test and then move to the carb cleaning and then to the idle circuit and report back.
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  7. #7
    Join Date
    Mar 2020
    Location
    Rhinelander
    --
    5
    It was so lean the motor was revving out by itself. The only way I brought it down was to hit the breaks in gear. And I will try to get a pressure tester and test it. I just thought it would be okay since it was running perfect then I had it bored and a new piston. It revs fine comes down fast and is super snappy. It’s just when it gets to 5th on the road it leans almost as if it’s not getting enough gas.

  8. #8
    Join Date
    Mar 2010
    Location
    Arizona
    --
    810
    Sounds like your needle jet is too lean. The needle jet controls fuel delivery from about 1/3 to 2/3 throttle, and then your main jet for the final 3rd. Drop the needle jet c-clip down by one slot.

  9. #9
    Join Date
    Mar 2020
    Location
    Rhinelander
    --
    5
    The thing is it runs great for a few passes and it doesn’t do it but I would say like 5-10 minutes of harder riding it will start to rev without throttle. I had an old 2 stroke tri moto and the fuel filter plugged and it leaned out of fuel and revved uncontrollably. Same way this one is revving out. It’s like I’m using fuel faster than the bowl fills. I ordered a pressure tester online so I will test that next week sometime.

  10. #10
    Join Date
    Mar 2020
    Location
    Georgia
    --
    48
    Oh I thought you met a air filter sorry. If it’s getting warm then doing it that means it is most likely pressure or the needle move it Down one spot from where it is now that would richen it up when you give it throttle.

  11. #11
    Join Date
    Jan 2012
    Location
    Carthage NY 250r rules
    --
    2,193
    Check your gas cap vent you should beable to blow through it.
    250r rules

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