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74 Honda ST90

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  • 74 Honda ST90

    Hey everyone.
    I'm looking for some help with a 74 Honda ST90 trail bike I'm working on for a friend. I have a strange problem with it, but first I'll you what was going on with it . When I first got it, my friend told me it was leaking gas, which it was comming out the overflow, and also it would run wide open with no throttle controll. Ok so after pulling the carb,I found a bad float, and replaced it. Set it to 21mm. Cleaned the carb passages, and jets,which wern't clogged, but figured I'd do it up right since I had it torn down. There are 2 adjustments on it. One for the idle and one for the mixture (if I'm correct). Got it all back togeather and back on the bike, got it started up and it was bogging down when you hit the throttle hard. Started to adjust the mixture and idle adjustments, it stalled out. couldn't get it started till I did a heavy cleaning on the plug. had carbon foul deap in it. Since then I have been able to start it when it's cold,but once it warms up, it starts bogging down, stalls and won't restart. The plug isn't fouled, and it's getting spark. I believe it's a fuel flow probelm,but I have gas in the carb, a line filter on it, because the internal screen has a hole in it. I've noticed it does not have a bowl vent, unless it's venting someother way. It seems it's getting plenty of gas to the bowl untill it runs for a while. There are no blockages in the carb or fuel lines. Is there something special that causes a flow problem with this type of bike. Someone said something about the gas cap on the tank, but I can't remember what it was. Checked the float to make shure it wasn't hanging up also. Air filter is off the bike, so it isn't choking out.
    Open road and power between your legs, nothing better!!

  • #2
    ok

    AIR FILTER IS OFF THE BIKE... will cause it to get a big gulp of air and bog out as it has no restriction. HTH
    Doug
    Doug Mitchell
    82 XJ1100 sold
    2006 Suzuki C90 SE 1500 CC Cruiser sold
    2007 Stratoliner 1900 sold
    1999 Honda Valkyrie interstate
    47 years riding and still learning, does that make me a slow learner?

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    • #3
      Could be the gas cap vent is plugged. To check it, as it begins to bog, take off the gas cap. If that fixes it you have found the problem.
      http://farm2.static.flickr.com/1241/1480921818_241eade448_s.jpg

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      • #4
        Sounds to me like vapor lock. When it stalls after warming up, does removing the gas cap cause a whoosh of air? If so, you've got a vapor lock issue somewhere.
        BobE
        Richmond, RI
        1980 XS1100G - "The Old Coot"

        PREVIOUS RIDES
        2005 Venture, 1993 Venture, 1983 Venture
        1978 Gold Wing, 1983 Gold Wing
        1975 CB500T, 1983 Husqvarna 250WR
        1981 XL500, 1975 CB750K5
        1981 CB900F, 1965 C200 (Honda 90)
        1968 Powell Challenger (Hairy-Chested Mini-bike)

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