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Thread: 86 250sx project won't start. Need help!

  1. #1
    Join Date
    Feb 2023
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    Deansboro
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    11

    86 250sx project won't start. Need help!

    I bought 2 trikes in pieces. An 86 and an 87 250sx. I have the 86 mostly back together. I'm doing a semi restore just removing rust and painting parts and fixing the mechanical stuff. I did the entire top end. New rings, gaskets, lapped the valves and adjusted them. Totally went through the carbs with all new jets and gaskets from 223cycles but the 86 came with an 85 carb which I don't imagine is a big deal. The wiring harness is a bit rough but I have what looks like good spark. I'm getting fuel to the cylinder I have the throttle and choke hooked up. Exhaust is on but it just will not fire. The starter is bad so I'm turning it over with a drill and when I open the throttle up it turns over quite a bit harder. It won't even cough with starting fluid. I'm stumped.

  2. #2
    Join Date
    Feb 2023
    Location
    Deansboro
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    11
    After screwing around with it more I decided to test the compression. It's only at 75 psi which is a lot lower than I thought it would be after putting new rings in it. So now I'm thinking I should put oversized rings in it but do I need to bore it also or can I just go with the bigger rings? I'm thinking that could be why it won't start because of the low compression. Am I on the right track?

  3. #3
    Join Date
    Apr 2014
    Location
    Edmond, KS
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    2,531
    Are you sure that your compression gauge is accurate? Sometimes they're not. If your cylinder wasn't worn too much, then I doubt that oversized rings will help. If they do, you should hev had your cylinder bored and installed an oversized piston too.

  4. #4
    Join Date
    Feb 2023
    Location
    Deansboro
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    11
    It's hard to know if my Guage is accurate to be honest. It's new but it's also a cheap one from Pepboys. The rings felt like a nice fit when I put the piston in. The only other thing I can think of is maybe the ignition timing is off somehow? I have no idea how to check that or adjust it if it is.

  5. #5
    Join Date
    Jul 2019
    Location
    Shelton
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    96
    Rings lap into the honed surface of a fresh cylinder. Just installing new rings into a used cylinder almost never works. At a minimum it needs to be honed, or the best way is to bore to the next oversize. Sometimes if the cylinder is in real good shape a hone and new rings is ok. It will never be right though because it's almost guaranteed to be out of round and tapered (more wear at the top). PM me if you need more into. You can't install oversize rings into a stock bore. They shouldn't fit or else you have a ton of wear.

  6. #6
    Join Date
    Apr 2023
    Location
    Florida Panhandle
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    10
    The 85 carb should work fine. I think the 86 just added some cold weather starting improvements. I agree with the other responses as well. Compression gauges can be bad, but 75 is where they wont fire. Boring is a pain and it can be difficult to find a machine shop these days. $90 should get it done somewhere though. You can go up .25 mm without any issues, but you will need oversized piston and rings. Do you know the history of the bike. It may have already been bored once and that would explain why standard piston and rings arent sealing.

  7. #7
    Join Date
    Feb 2023
    Location
    Deansboro
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    11
    So it's sounding like I need to either bore this cylinder and get a oversized piston and rings or buy another cylinder with it's piston that came with it.

  8. #8
    Join Date
    Mar 2023
    Location
    Earth
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    78
    Quote Originally Posted by Heavymand View Post
    So it's sounding like I need to either bore this cylinder and get a oversized piston and rings or buy another cylinder with it's piston that came with it.
    You probably assembled it wrong or adjusted the valve clearance incorrectly.

    Stop throwing parts at stuff and start reading and measuring.

  9. #9
    Join Date
    Feb 2023
    Location
    Deansboro
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    11
    I'm not throwing parts at it belive me the less i have to buy the better. The only reason it got new rings was because the rings were stuck in the piston originally and I broke them getting them out. I've assembled and timed everything per the service manual so far. I haven't measured the cylinder though.

  10. #10
    Join Date
    Mar 2023
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    Earth
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    Quote Originally Posted by Heavymand View Post
    I'm not throwing parts at it belive me the less i have to buy the better. The only reason it got new rings was because the rings were stuck in the piston originally and I broke them getting them out. I've assembled and timed everything per the service manual so far. I haven't measured the cylinder though.
    Well I'll be damned.

  11. #11
    Join Date
    Feb 2023
    Location
    Deansboro
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    11
    Yup so now I'm hear asking the more experienced people for guidance. The 87 I'm not worried about. It has 120psi of compression on my tester so I'm leaving that alone. The guy I got these from had the right side cover off of both engines though and both reverse shafts installed wrong. The spring wasn't under tension in the 86 and the 87 had the shaft rounded off with the spring hanging out of the side cover while the installed the cover. These things have been a lot of work so far but like I said I bought them almost completely torn down so I knew they would be.

  12. #12
    Join Date
    Mar 2023
    Location
    Earth
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    78
    Quote Originally Posted by Heavymand View Post
    Yup so now I'm hear asking the more experienced people for guidance. The 87 I'm not worried about. It has 120psi of compression on my tester so I'm leaving that alone. The guy I got these from had the right side cover off of both engines though and both reverse shafts installed wrong. The spring wasn't under tension in the 86 and the 87 had the shaft rounded off with the spring hanging out of the side cover while the installed the cover. These things have been a lot of work so far but like I said I bought them almost completely torn down so I knew they would be.
    If you have the opportunity to measure the bore accurately in 6 places like it should be do that. You cannot measure a bore with a vernier caliper.

    Be sure the valves arent tight at tdcc. Very common when rebuilding a topend.

  13. #13
    Join Date
    Apr 2023
    Location
    Florida Panhandle
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    10
    Hang in there Heavymand. Compression seems to be the issue that you have identified. Especially if your gauge seems to be reading correctly on the other machine. I would bore before trying to find a secondhand jug in good shape. By the time you get it all figured out you'll be an expert on Honda 3Wheeler. As a side note - sometimes I throw parts at stuff because it is "cheaper" than spending the time to dig through things.

  14. #14
    Join Date
    Mar 2023
    Location
    Earth
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    78
    Quote Originally Posted by SoFarKingSlow View Post
    Hang in there Heavymand. Compression seems to be the issue that you have identified. Especially if your gauge seems to be reading correctly on the other machine. I would bore before trying to find a secondhand jug in good shape. By the time you get it all figured out you'll be an expert on Honda 3Wheeler. As a side note - sometimes I throw parts at stuff because it is "cheaper" than spending the time to dig through things.
    Sometimes you can throw statements at people because its faster and more efficient at getting them to offer info than asking polite questions. I got exactly the response I needed to skip multiple questions.

  15. #15
    patriot1 is offline At The Back Of The Pack Arm chair racerAt the back of the pack
    Join Date
    Mar 2020
    Location
    Palestine, AR
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    356
    Heavymand:

    Please read my "350x Saga" thread. It's still ongoing but sounds very similar to your situation.

    G&H Honda in TN offers great deals on top end kits, check them out especially if you don't have a machine shop close by.

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