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Thread: ATC90 (132cc) help - idles but can't take throttle (FIXED!) now need seat advice

  1. #16
    Join Date
    Jul 2009
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    South Florida
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    6,722
    Look for a long style aftermarket manifold and I bet that fixes your problem .
    I have my Doubts that larger jets are the fix but it can’t hurt to try .
    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

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  2. #17
    Join Date
    Nov 2015
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    Davenport iowa
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    You never did say what size main you are running
    90 nickolson Bored and Stroked "The Good"

    Big Bore 110 Pauter frame "The Bad"

    90 Bored and Stroked “vey’s frame” "The Ugly"

    110 JSC frame Bored and Stroked
    flat track build. “Shop trike”

    1974 original 90 X 2

    1974 Original 70.

  3. #18
    Join Date
    Jul 2009
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    South Florida
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    Said he was using a 90 main .
    Quote Originally Posted by DAM shop View Post
    You never did say what size main you are running
    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

  4. #19
    pismorat's Avatar
    pismorat is offline At The Back Of The Pack Arm chair racerFirst time rider
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    Dec 2005
    Location
    San Diego
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    207
    I pulled the 90 and put in a 120. No change. Then I upped it for fun to a 150, still nothing. Makes me wonder if there is a jammed passage in the carb still or the timing is off, even though its set right. It will idle all day long, just starts missing when the slide goes up and doesn't increase engine speed. I'm going to try a compression test this weekend...not sure what that'll tell me though.
    '78 Honda ATC90 (132cc)
    '83 Honda ATC70 (88cc)
    '85 Honda ATC250R
    '86 Honda TRX200SX
    '04 Honda 400EX
    '73 Honda Trail 90
    '01 Honda XR70R (125cc)
    '16 KTM 500 EXC

  5. #20
    Join Date
    Jul 2009
    Location
    South Florida
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    Long style manifold .
    If your 100% sure the electrical is ok then it’s the manifold .


    https://www.ebay.com/itm/36391827071...Bk9SR9Kh9vP-YA
    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

  6. #21
    Join Date
    Jun 2013
    Location
    Oceanside, CA.
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    610
    I agree with shortline10, long manifold. It's been years since I've jetted 90's but as a stretch remember a friend who had cleaned their carb and lost the needle jet, gave the same symptoms.

    "HJ" Click image for larger version. 

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    ’84 YT60
    ’85 350x (423cc) with ’81 XL500 head conversion
    ’83 XR500 (628cc) converted 3 Wheel hybrid
    ’73 CB750 K3 converted 3 Wheel hybrid
    ’86 TRX250R chassis XR650L engine hybrid
    ’89 TRX250R (stock )
    ’90 LT500 Quadzilla
    ’85 FL350 Odysses ( water cooled head )
    Lost (sold) but not forgotten ’80 ATC 110 (205cc on alcohol ) ’83 200x ( 222cc ) ’83 200x ( 185s eng ) ’85 350x ( stock )
    added to the collection recently, (2) '70 US90 Aquarius Blue and '74 ATC90 Daytona Orange

  7. #22
    pismorat's Avatar
    pismorat is offline At The Back Of The Pack Arm chair racerFirst time rider
    Join Date
    Dec 2005
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    San Diego
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    207
    Hey all. thanks for sticking with me here. I disassembled the carb again over the weekend and boiled it, then blew all the passages out again to try and, for the umpteenth time, verify it is clean. No changes. I did a compression test and its at 175psi. This makes me wonder if I shouldn't have the timing set at "0", or if the advance is working. What's an easy way to test for that...before I go after a long manifold?
    '78 Honda ATC90 (132cc)
    '83 Honda ATC70 (88cc)
    '85 Honda ATC250R
    '86 Honda TRX200SX
    '04 Honda 400EX
    '73 Honda Trail 90
    '01 Honda XR70R (125cc)
    '16 KTM 500 EXC

  8. #23
    Dave8338's Avatar
    Dave8338 is offline At The Back Of The Pack Arm chair racerAt the back of the pack
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    Central MN
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    378
    Quote Originally Posted by pismorat View Post
    So I've been working on a '78 ATC90 for some time now and trying to get it running so its usable. It has a Bandito frame, 132cc kit, large Mikuni carb, Powroll intake, and a few other period-correct trick parts. I have put new points, condenser, and coil in it. The valves are adjusted and the timing is spot on. It starts with the choke on and the idle fluctuates a bit till its warm, then with the choke off it idles perfectly and will all day long. Any time I try to crack the throttle though, it starts sputtering and wants to die. I let off, and it idles again, so that tells me the idle circuit is fine, but something it wrong with the main? With the air filter off, gas almost comes spraying backwards out the inlet as I try to increase the throttle. I have taken the carburetor apart and cleaned it more times than I can count. I have played with the needle in all positions, messed with the air screw (idle circuit), and cannot seem to make it any better. My father-in-law ran it as is 25 years ago, so I am thinking the jetting should be close enough. Does anyone have an idea what to go after next?
    Not knowing anything about engines, ignition systems, or carbs, rubber band powered airplanes, model trains, or hydroplanes; I would suggest replacing your condenser and while you’re at it, throw a cheap coil on it too.

    If you’re burping up fuel you’re not short on fuel. Just my ignorant.02 for what that’s worth.
    The Goal... All I Need Is The Time...

  9. #24
    pismorat's Avatar
    pismorat is offline At The Back Of The Pack Arm chair racerFirst time rider
    Join Date
    Dec 2005
    Location
    San Diego
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    207
    I have put new points, condenser, and ignition on i at the beginning. I am starting to lean towards a timing or advance issue since it was able to rev up a few weeks ago, though not great, better than now. Then I did some things to it, setting the timing being one of them, and now it is far worse. Maybe the thing needs more advance or the mechanical advance isn't working right. That'll be my next area or fous.
    '78 Honda ATC90 (132cc)
    '83 Honda ATC70 (88cc)
    '85 Honda ATC250R
    '86 Honda TRX200SX
    '04 Honda 400EX
    '73 Honda Trail 90
    '01 Honda XR70R (125cc)
    '16 KTM 500 EXC

  10. #25
    Join Date
    Jul 2009
    Location
    South Florida
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    6,722
    If you don’t want to purchase a long manifold just make a makeshift one to try lol .
    Needs about two more inches for the fuel to mix better .
    A 2” block of wood and a hole saw and can be made up in a few minutes , this would be just for temporary trial of coarse .
    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

  11. #26
    Join Date
    May 2013
    Location
    Brownsville, Tn.
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    Long manifold, Long Manifold, Long manifold...... POSA or Long BAPP work the best. It will make a difference. The short manifolds and a Mikuni are a female dog to get right.

    BTW nice oldschool bike. The frame is a Nicholson and it appears to have HD front forks.
    * 1978 ATC 90/180 Pauter PJ1 / Springer "Team BAPP" Bike *

    * 1980 ATC 110/180 "Danny's Machine Works" 3D Sprint Dune Bike *

    * Nicholson 500 Race Bike *

    * HPATC Yamaha RD350 "Big Moe" Trike *

  12. #27
    Join Date
    Jul 2009
    Location
    South Florida
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    Hey Joseph maybe I should of said it like a broken record to
    But what the hell do I know , I’ve only built a few hundred of these motors




    Quote Originally Posted by Joseph Farrow View Post
    Long manifold, Long Manifold, Long manifold...... POSA or Long BAPP work the best. It will make a difference. The short manifolds and a Mikuni are a female dog to get right.

    BTW nice oldschool bike. The frame is a Nicholson and it appears to have HD front forks.
    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

  13. #28
    pismorat's Avatar
    pismorat is offline At The Back Of The Pack Arm chair racerFirst time rider
    Join Date
    Dec 2005
    Location
    San Diego
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    207
    It's fixed!! I ran it this afternoon and its screams (for a non-suspended ATC 90). I am sure it'll run better with a long manifold down the road, but I found the true issue. I dove back into the timing and went all the way to the camshaft. The pin coming out of it was cocked, so as everything from that point out was set from the misplaced pin, the timing was way off. I set the timing by eye (using a mutli-meter was measuring continuity even when separation started) and the thing started and revved no problem. Had a good time blasting it around my in-laws' property today and now will button up a few loose ends so I can take it flat tracking in a couple weeks. More pics to come...

    Thanks again for being patient and to all those who helped me track this gremlin down!
    '78 Honda ATC90 (132cc)
    '83 Honda ATC70 (88cc)
    '85 Honda ATC250R
    '86 Honda TRX200SX
    '04 Honda 400EX
    '73 Honda Trail 90
    '01 Honda XR70R (125cc)
    '16 KTM 500 EXC

  14. #29
    pismorat's Avatar
    pismorat is offline At The Back Of The Pack Arm chair racerFirst time rider
    Join Date
    Dec 2005
    Location
    San Diego
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    207
    Now I need help with the seat... I have the set of fiberglass fenders and made new seat pan attachment pieces, but I cannot find seat foam for it anywhere. I can get a cover off eBay, but that does me no good without formed foam. My usual upholstery guys don't have the time to work on it before I need it done in 10 days. What have you all used for seat foam, anything you can order that is close that need minimal trimming? I'd hate to take this thing to the flat track having to sit on a pillow, but I will if I have to.
    '78 Honda ATC90 (132cc)
    '83 Honda ATC70 (88cc)
    '85 Honda ATC250R
    '86 Honda TRX200SX
    '04 Honda 400EX
    '73 Honda Trail 90
    '01 Honda XR70R (125cc)
    '16 KTM 500 EXC

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