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Thread: 84 atc 70 - idles but won't accept throttle

  1. #1
    Join Date
    Feb 2019
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    84 atc 70 - idles but won't accept throttle

    I posted some of this information in a different thread earlier, (just realized I can start a new thread, so here goes).

    Bought two atc 70's, a Christmas Special and an 84. The 84, I'm trying to get running so I can ride it. The Christmas Special will be restored to glory.

    The 84 ran at a very high idle when I first got it, and barely would gain rpm's when you gave it throttle, it would rather stall. I cleaned the carb and it got worse?!?!
    I have since adjusted the valves and points and tightened the timing chain tensioner. I cleaned the carb extensively; it's the stock carb with the stock jets in there, which I believe are 38 and 58. It seems like a fuel problem but I have noticed some indication of blowback through the carb.
    I have good spark.

    Went over everything last night again and it fired up first pull but seemed to be giving me the exact same issue. It idles but will stall if you go to give it gas.

    Any thoughts on this matter oh knowledgeable three wheeler forum?

  2. #2
    fabiodriven's Avatar
    fabiodriven is offline Aspiring romance novel cover model, and the Official 3WW slayer of thieves and swindlers. Catch me if you can
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    It's likely you have a leak at the intake manifold gasket.
    85 Tri-Zinger 60
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  3. #3
    Join Date
    Jul 2018
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    Yep, most likely a vacuum leak. Ever so gently mist some starting fluid in and around the carb and intake. If the motor speeds up, you found it.
    Amateur Resurrectionist

  4. #4
    Join Date
    Feb 2019
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    I like those ideas and have a new manifold gasket that I can try. Before the most recent adjustments, I attempted to spray either in the air filter and it didn't change anything.

    Appreciate the suggestions.

  5. #5
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    If the points are old replace them , OEM only , they are big part on how the spark is advanced when you accelerate . Their is no mechanical spark advancer or CDI , itís all done threw the points , adjust them to .016 .

    Itís also very important on the stock carburetor to have a perfectly sealed air box which includes the intake boot .
    78 atc 90/180cc Dickson Full Suspension
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  6. #6
    Join Date
    Jul 2016
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    Kentucky
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    Agreed. I’d replace the gaskets, replace and set the points with a light bulb if you can and order a new carb. They’re cheap, just be sure to tighten up that screw on the butterfly inside before you install it, I’ve had several come loose. Might as well check the valves too. Be sure you’re too dead center on the compression stroke for valve adjustment. Otherwise it might not ever start for you.

  7. #7
    Join Date
    Feb 2019
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    Update:

    It wasn't a vacuum leak. I tried propane and either and neither made any difference, actually you can spray either in the air filter and it doesn't do anything.

    Did a compression test and it was low, like 88psi. So I figured why not just put this 88cc kit on it. I did that Saturday night and unfortunately I still have the same problem. The bike starts and idles fine, but won't rev up. It doesn't exactly stall either when you give it gas, just doesn't do anything. We did notice the valves weren't seating 100% so we lapped them and the result put us in spec according to the manual.

    I suppose I'll buy a new set of OEM points, although the points look new, maybe they're aftermarket and junk? I had the points set at .035mm or something to that affect...following the service manual.

    I have a metal mesh air filter on it, not the stock air box so it's definitely getting enough air and when you choke it that's no improvement so I don't think that air is the issue.

    Again; I appreciate the suggestions. Thanks!

  8. #8
    Join Date
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    I will get flamed for it by the purists but a points delete kit is cheap. They're pretty simple to wire up and you don't have the points to deal with anymore. Points are great....until they ain't. More to them than just the gap. The contacts need to be parallel to one another. Not sure how the dwell can be adjusted as I've never touched Honda points to my knowledge.

    Anyway...it's an option. I've done it to several older engines and it always works fine.
    Amateur Resurrectionist

  9. #9
    Join Date
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    Your problem is the missing “AIR” box , the stock carburetor will not accelerate without it .
    A clamp on filter will not work on a stock carburetor !

    Your options are either buy an aftermarket carburetor or try and find an OEM complete air box assembly .
    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

  10. #10
    Join Date
    Feb 2019
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    Can someone point me in the right direction to purchase OEM points? And possibly an aftermarket carb that would be suitable.

    This red 84 came with a kehin on it that's not the stock carb, but I am using the stock carb (from the christmas special) to test with since I know it's the right one. I have tried the carb that came on the bike multiple times, but maybe it's got the same issue because I'm not using a stock air box??? Wouldn't the choke (at some level) replicate the restriction of the stock air box and therefore let it run right, even if it was just for a second? I'm asking because that never happens.

    Again, the help is appreciated.

  11. #11
    Join Date
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    Part number 1 and 3 should be replaced at the same time , both available new from Honda .
    https://www.partzilla.com/catalog/ho...0-a/alternator

    These guys are local to me and their carburetors seem to work good .
    https://www.ebay.com/itm/Honda-ATC-7...ty!33331!US!-1
    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

  12. #12
    Join Date
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    Quote Originally Posted by shortline10 View Post
    Part number 1 and 3 should be replaced at the same time , both available new from Honda .
    https://www.partzilla.com/catalog/ho...0-a/alternator

    These guys are local to me and their carburetors seem to work good .
    https://www.ebay.com/itm/Honda-ATC-7...ty!33331!US!-1
    I picked these items up and also a new head. One of these things should do it! I'm getting frustrated and I'm just going to take the anger out on the throttle...eventually!

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