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Thread: Atc 70 backfires

  1. #1
    Join Date
    Mar 2018
    Location
    Tulare, California
    --
    21

    Atc 70 backfires

    So I am having trouble getting my 70 to run correctly. Here is what has been done to it.
    - Piston and ring replaced same as stock
    - Spangler atc 70 stock replacement carb installed
    - points have been adjusted to 0.35
    - ignition timing is correct
    - Carb has been cleaned a handful of times but nothing is ever dirty.
    - At first bike would only run on choke but that has been fixed, I have a aftermarket k&n filter on it. Iím not sure what else to look at as of right now. Bike will idle fine but when you go to give it gas it boggs out. I have been told it is the jets but Iíve never went down that road. Somebody please help!!!!!!!!!

  2. #2
    Dave8338's Avatar
    Dave8338 is offline At The Back Of The Pack Arm chair racerAt the back of the pack
    Join Date
    Jan 2013
    Location
    Central MN
    --
    363
    Sounds like it is running lean on the main jet, likely a result of the air filter change to a high-flow K&N. Have you oiled the filter and blotted off any excess oil? I assume it is backfiring through the exhaust? If not and it is through the intake, it is typically an ignition/timing issue. Plug gapped correctly? I'll admit to not being an ATC 70 expert however, all four-strokes run correctly with the same issues addressed.
    The Goal... All I Need Is The Time...

  3. #3
    Join Date
    Jul 2009
    Location
    South Florida
    --
    5,870
    Trying to make a stock carburetor run with an open air filter will make the exact symptoms your describing .
    Can try a larger main jet or buy a factory air box set up .

    Their are at least 50 threads on this same atc70 topic .
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    Performance Shop is Open PM me for Service

    My Feedback http://www.3wheelerworld.com/showthr...ck+shortline10

  4. #4
    Join Date
    Jul 2009
    Location
    South Florida
    --
    5,870
    Try choking the air filter with a rag and see if you can get it to rev up , if yes you’ll need a larger main jet .
    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
    84 atc 200x Powroll My race bike from 80's
    83 atc70/108cc Powroll blue Xmas Special
    81 atc185s HP-ATC full suspension

    Performance Shop is Open PM me for Service

    My Feedback http://www.3wheelerworld.com/showthr...ck+shortline10

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