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Thread: just rebuilt my atc70 and now no start

  1. #1
    Join Date
    Mar 2018
    Location
    Halifax, NS
    --
    34

    just rebuilt my atc70 and now no start

    I just rebuit my atc 70 1983. Quite the rebuild... crankshaft, engine case, head (all used but good) and now it won't start...
    Compression seems quite good when I crank it.
    There is good spark. I checked the cam timing and it looks good (when flywheel is at T, the O is on the far end of the head)
    Gap appears good on the point and spark is good. Fuel makes it in the cylinder as after cranking like a crazy mo... the spark plug gets wet and I can burn the vapors from the cylinder. What drives me crazy is that there is nothing... it doesn't even fire a bit...
    What does the neutral safety switch do? How do I bypass that? *(but given I have spart I would think that the switch is good?)
    Thanks for any pointers!
    David

  2. #2
    Join Date
    Jun 2010
    Location
    Cold Lake, Alberta, Canada
    --
    2,592
    My first action would be to get a number on a compression test. Should probably be around 140#.
    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)
    1984 Big Red 200es w/85 250 front end
    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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  3. #3
    Join Date
    Nov 2015
    Location
    Davenport iowa
    --
    826
    Are you running the stock air box?
    90 nickolson Bored and Stroked "The Good"

    Big Bore 110 Pauter frame "The Bad"

    90 Bored and Stroked "The Ugly"

    110 Nickolson Bored and Stroked "Waterloo"
    flat track build.

    1974 original 90 X 2

    1974 Original 70.

  4. #4
    Join Date
    Mar 2018
    Location
    Halifax, NS
    --
    34
    Better find that compression tester somewhere...
    Yep, still the original airbox.
    My valve seats were quite rough so maybe the valve is not sealing properly even after the lapping...

  5. #5
    MrConcdid is offline At The Back Of The Pack Arm chair racerFirst time rider
    Join Date
    Nov 2019
    Location
    Florida
    --
    202
    my guess is your timing is 180 out of phase. T/F comes up twice per cycle. TDC is the first T/F of the cycle.
    Try another spark plug, I had one that would spark outside the cylinder but not under compression.


    MrC.
    Last edited by MrConcdid; 03-20-2020 at 11:24 AM.

  6. #6
    Join Date
    Jul 2009
    Location
    South Florida
    --
    6,099
    Cam / timing sprocket is a 3 bolt setup so it’s idiot proof you can’t set the timing 180 degrees out when the O and T are set .


    Quote Originally Posted by MrConcdid View Post
    my guess is your timing is 180 out of phase. T/F comes up twice per cycle. TDC is the first T/F of the cycle.
    Try another spark plug, I had one that would spark outside the cylinder but not under compression.


    MrC.
    78 atc 90/180cc Dickson Full Suspension
    76 ATC90/180cc Nicholson
    77 atc 90 Dickson Full Suspension
    84 KLT 110/123cc Powroll Racer from 80s
    87 atc 125m stock
    84 atc 200x Curtis Sparks
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  7. #7
    Join Date
    Mar 2018
    Location
    Halifax, NS
    --
    34
    Alright!! Started! It turns out the new plug was bad. There was spark but most of the time between the plug body and engine not between the electrodes. New plug and it fored right up!
    Now another question. The secondary cam chain adjuster (the one below the engine) how do we know the correct position of the adjuster bolt in there? Tighten until the chain is jot noisy?
    Any idea of where to start?
    Thanks!
    David

  8. #8
    MrConcdid is offline At The Back Of The Pack Arm chair racerFirst time rider
    Join Date
    Nov 2019
    Location
    Florida
    --
    202
    So it was the plug, nice.
    MrC.

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