No top end 1985 ATC250r
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  1. #1
    Junior Member abcsgarage's Avatar
    Join Date
    Apr 2019

    No top end 1985 ATC250r

    So long story short I just bought a 1985 ATC250R that’s been sitting for at least 8 years in an enclosed trailer. I got it by happen chance, my uncle owned this bike and made it very nice back in the early 2000s. 15 years later I aquired the bike and it’s only been ridden twice since my uncle owned it.

    Anyways, I got all the old gas out of it and cleaned out the carb and jets. I ran 32:1 Golden Spectro two stroke mix and non ethinol 92 octane fuel. Cleaned the air filter, changed the oil and got it fired up. Idles fantastic and has decent throttle response under a load. First ride out which was at the local sand dunes on the Oregon coast which is at sea level. I had all sorts of fuel related problems getting fuel into the bowl. Got that sorted out and I have a solid bottom to mid range, the bike gets right to where the power should really come alive and it falls flat and almost sounds like it’s popping. I haven’t messed with anything yet other then just clean the carb. Still running the original jets from when my uncle owned it. So I have a hard time beliving it’s a jetting problem. I just took the reeds out for inspection and they look fine no noticeable cracks or wear. Cylinder/piston also looks fine on the one side.

    I’ve ridden many many two strokes and don’t have a problem running them wide open and I did get it into 6th running flat out down the dune as hard as I could thinking maybe it was loaded up but alas the kick to the nuts never came. Anyone have any ideas as to what my issue might be? Can a CDI cause a high RPM issue and still run great on the bottom end? Would 32:1 cause an issue as well? My uncle mentioned he always ran 40:1 which is what I usually do but I panic’d when I saw the 20:1 sticker on the frame. Compression is really strong as well.

  2. #2
    Senior Member atvguy's Avatar
    Join Date
    Jul 2014
    Race fuel
    8 or 9 plug .020 gap
    make sure didn't over oil filter


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