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Thread: 1978 Honda atc 90 wont run right.

  1. #1
    Join Date
    May 2020
    Location
    Wisconsin
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    1

    1978 Honda atc 90 wont run right.

    Hey guys looking for some help here. I have a 1978 Honda atc 90. Was given to me and was told it had low compression. Did a compression test and found that it only had 25 psi. Checked valve clearance, found both valves has 0 clearance and were holding the valves open. Adjusted valves and got 60 psi on compression. Still low. So I took the top end apart. Found the piston and cyl scored. So I ordered a factory cyl, and piston kit. The cylinder head was egged out for where the camshaft rides. So I did some searching. Turns out the 110 head is the same but the valves are different. So I put it all together hoping it would work with a little carb adjustment or a 110 carb. It will only run on choke and revs high. When the choke is off. You have to keep pressing the throttle and is runs very poorly. Has new points, and spark plug. And verified the ign timing a millions times. Has a very strong blue spark. Have tired a new 90 carb and a 110 carb. Still runs very poorly. Can't figure this one out. Some please help me out if you can. Any help would be much appreciated.

  2. #2
    Join Date
    Jun 2010
    Location
    Cold Lake, Alberta, Canada
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    2,969
    Sound like you have an air leak between the carb and the motor. Are the O-rings good? When it's running, spray a little carb cleaner around those areas to see if it sputters.
    Trikes
    1970/71 US 90 (Aquarius Blue)
    1970/71 US 90 (Future Resto Project)
    1972/73 US 90 Camo Project (110 Big Bore)
    1972/73 US 90 Green
    1977 ATC 90 w/83 110 motor (Fugly)
    1982 ATC 70
    1983 ATC 70 (Ladybug)
    1973 ATC 70

    1965 Marketeer 3 Wheel Golf Cart with 1986 Honda 250 drivetrain

    TF 2015

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