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Thread: 1984 YTM200L idles too high once hot.

  1. #1
    Join Date
    Feb 2020
    Location
    Warminster PA
    --
    5

    Smile 1984 YTM200L idles too high once hot.

    Hi All, I'm new to this forum. I signed up because I'm having an issue with my 1984 ytm200L and I couldn't seem to find a thread that described my issue. If one exists, apologies for the long winded post.

    I bought the trike recently and replaced the carb because it was leaking and the choke didnt work. The new carb is set to factory settings that I found on this site. There are still a couple issues that may or may not be related.

    First...I can get the trike started no problem and it will idle once it is warmed up a little. Once it is running for a while, maybe 5 or 10 minutes, the idle gets weird. It will rev up then down randomly. If I bump the throttle, it will settle down into a nice idle again sometimes, but sometimes it will take a few seconds to get back down to idle. Then it will rev up and down randomly again.

    Second...the piston rings are toast. I'm getting a lot of blow by but I'm not sure that could be related to the idling problem.

    The diagnostics I've tried are mostly limited to looking for vacuum leaks and resetting the carbeurator (like dozen times).

    I built a smoke machine and found a tiny leak where the throttle cable hooks up to the carb, and on the throttle cable itself where the plastic meets metal right near the end. This doesnt change after heating up though. I dont know if it is enough to cause the problem.

    I would be interested if there were any ideas on diagnostics I could try so any ideas are welcome.

    It would be even better if someone has had the exact issue and has a solution already


    Any help is much appreciated!
    -Eric

  2. #2
    Join Date
    Apr 2011
    Location
    Mexico
    --
    9,003
    Check first that your throttle cable is free moving and has at least 1/8" of free play along the entire turn radius of the handle bars. Then check that the rubber manifold between the carb and the head has no cracks. There are two styles used on the YTM, the one that bolts to the head on the newer years uses an O-ring that could be cracked. If that checks out I would make sure the float height is correct. Nothing else comes to mind.

  3. #3
    Join Date
    Feb 2020
    Location
    Warminster PA
    --
    5
    Thanks for the ideas. I'll take a look at the manifold O-ring when I get home today or tomorrow. The O-ring from the carb to the manifold is fine since it is brand new.

    How could the float height change the idle? I did need to adjust the float height initially because it was leaking fuel from the overflow so the float wasn't stopping the fuel flow. That no longer happens but Is there a spec for float height? If so, where do I measure to and from?

  4. #4
    Join Date
    Apr 2011
    Location
    Mexico
    --
    9,003
    If you were leaking gas out of the overflow tube it’s more likely that the needle and seat were dirty than a float height issue unless the tab was badly distorted.

    I highly recommend that you buy a new needle and seat before you start chasing your tail around trying to find other problems, because if its worn it can leak intermittently and that will cause all kinds of inexplicable symptoms.

    If you haven’t already, I would also make sure that fuel is flowing freely through your petcock/fuel line. If its partially plugged you can end up running the bowl of the carb down and creating problems.

    Your float height is critical to proper carburetor function in ways that I could ever fully explain or understand, but the simplest way I can try to explain it is to imagine sucking on the straw of a cup of soda as it starts to run out of fluid and take on air. If this happens in your carburetor it will simulate a lean condition and revs will go up, same as what I mentioned about a plugged petcock. On the other hand if your float level is too high fuel can displace air space meant for positive pressure that’s needed to allow the vacuum of your engine to draw fuel up through the passages.

    Here’s a link that uses the super accurate height check method of a clear tube against the float bowl, or you can research how to set float heights and set it to 25mm. Lots of videos on Youtube to show you how.

    http://www.3wheelerworld.com/showthr...e-Fuel-Mixture

  5. #5
    Join Date
    Feb 2020
    Location
    Warminster PA
    --
    5
    Awesome info, thanks!

    I will check the O-ring between the manifold and the head and the float height again. That picture was worth a thousand words.

    The needle and seat should be ok because the carb is new.

    I'll check fuel flow from the petcock too. I get fuel for sure, but the lever is a little gummy so it might not be flowing fast enough.

    As soon as I do all those checks I will report back.

  6. #6
    Join Date
    Apr 2011
    Location
    Mexico
    --
    9,003
    Quote Originally Posted by Ericn View Post
    The needle and seat should be ok because the carb is new.
    Whoa! How did we get from leaking carburetor and adjusting float height to new carburetor? Are you saying that a brand new carburetor was leaking on you and you adjusted the float height? This isn’t one of those $19.99 Chinese eBay carburetors is it?

  7. #7
    Join Date
    Apr 2014
    Location
    Edmond, KS
    --
    2,531
    Quote Originally Posted by El Camexican View Post
    Whoa! How did we get from leaking carburetor and adjusting float height to new carburetor? Are you saying that a brand new carburetor was leaking on you and you adjusted the float height? This isn’t one of those $19.99 Chinese eBay carburetors is it?
    He did say in the first post that he replaced the carb because it was leaking. The next sentence starts out with "the new carb". Those cheap, Chinese carbs can make all kinds of crazy things happen. Your best bet is to rebuild the original one.

  8. #8
    Join Date
    Feb 2020
    Location
    Warminster PA
    --
    5
    It is a cheap chinese one. I read somewhere else (I dont remember if it was here or some other forum) that those are usually ok but I was just assuming. Happy to be informed otherwise.

    I might be able to rebuild the old one, but the previous owner jacked up the choke valve. I may be able to straighten it out but I'm not sure.

    Where do you suggest sourcing parts? It looks like bike bandit has a bunch of stuff but mostly individual parts. ATVworks might also. The dealership or is that going to be ridiculous?

  9. #9
    Join Date
    Apr 2011
    Location
    Mexico
    --
    9,003
    I might have some spare parts. Post photos of what you need.

    jetsRus.com is a great source for carb parts. They never answer the phone now. You can also try Sudco. They usually pick up.

  10. #10
    Join Date
    Feb 2020
    Location
    Warminster PA
    --
    5
    Quote Originally Posted by El Camexican View Post
    I might have some spare parts. Post photos of what you need.

    jetsRus.com is a great source for carb parts. They never answer the phone now. You can also try Sudco. They usually pick up.
    Thanks for all the info.

    I think I fixed both issues.

    I reset the float a bunch of times then I looked at the needle and seat (on the new cheap carb) and I thought I could see a little nick in the seat. I rebuilt the old carb with new o rings and the bowl gasket from the new carb. I was able to straighten out the choke valve enough that it moves freely. Swapping the carb seems to have fixed the fuel issue.

    I had it idling for 30 mins and was riding around and it seemed great.

    I added a slightly heavier spring on the throttle cable and that fixed the surging issue.

    Thanks for all the input and I'll update if new issues come up.

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