TTR 125 Problems

Discussion in 'Mini Racing' started by SuddenBraking, Jan 4, 2020.

  1. SuddenBraking

    SuddenBraking Well-Known Member

    Do you have a 1290 you track sometimes?
  2. SuddenBraking

    SuddenBraking Well-Known Member

    Lol, you may be on to something there......definitely flying a bit blind with how to seat the throttle assembly in this new carb. I'll take a look at it when I break it down and see how I may have fucked it up.
  3. SuddenBraking

    SuddenBraking Well-Known Member

    Update - fairly certain the carb needs to be adjusted as I "invented" the way I installed it with a plate I'd never seen (presumably to hold the throttle cable) - will take pics so you guys understand what I mean.

    Related to the engine, took the engine plug covers off (thanks for making them out of swiss cheese, Yamaha) and am checking the valves now. Never done that before so it should be interesting, but if I've indeed found TDC (fairly certain I have - pic is attached), then my valves are tight as fuck. Current plan is to get them in spec, fix the carb assembly, and then fingers crossed that this SOB runs like it used to.

    Attached Files:

  4. pscook

    pscook Well-Known Member

    Rotate the engine one more full revolution and check the valves again. You might have it at the "wrong" TDC.
  5. SuddenBraking

    SuddenBraking Well-Known Member

    So, checked the valves and they're all good. Brand new carb/spark plug should be working fine and finally went out and tried to start the SOB and it idled weakly for a bit and then died. Then it wouldn't start again after kicking the shit out of it.

    Would really like to troubleshoot this as I'm guessing it's something stupid but the risk of it being a serious engine problem (I'm a big boy and I rev the fuck outta that little kid bike) makes me hesitant to invest too much time. TBD on next steps.
  6. britx303

    britx303 Plagued with FZRs...........

    Check the float/fuel height in bowl? Our brand new ebay carb had machining debris in the needle valve and would either not allow fuel in or would not stop the fuel and would overflow. Kept f*cking with the float height until we did a disassembly of the new carb and found the crap in there.
  7. damiankelly

    damiankelly Well-Known Member

    Make sure you have fresh gas in it...they like fresh gas
  8. SuddenBraking

    SuddenBraking Well-Known Member

    Yeah, it's got Tru Fuel in it (only 30 days old) so it's not the gas.

    It's probably a carb problem but it's clearly outside my skillset as I've rebuilt the current carb and then installed a brand new aftermarket one and neither worked.
  9. joec

    joec brace yourself

    Could it be the rev box?
  10. SuddenBraking

    SuddenBraking Well-Known Member

    Not a clue, but it's running like absolute dogshit.

    Here's a quick video I put together.

  11. Kurlon

    Kurlon Well-Known Member

    On choke still, is it HOT yet? TT-Rs are stupidly cold blooded. Also, air leak?
  12. damiankelly

    damiankelly Well-Known Member

    Take the cap off and see if it runs ok could be the hose in the cap is clogged— those after market things can clog—- —-I dunno
    Last edited: Jan 26, 2020
    pscook likes this.
  13. britx303

    britx303 Plagued with FZRs...........

    Did you recheck that the slide spring/needle are installed correctly? Seems like its bouncing around in there jumping from normal to overly rich and back to normal with the intake pulses causing it to jump around. Can you do a short disassembly video of the slide assembly for us to see?
  14. SuddenBraking

    SuddenBraking Well-Known Member

    I appreciate the insight and I would except I think I'm done futzing with it and am just going to send it to the pros to fix. Will report back on what the issue(s) were once I get some more info.
  15. Shenanigans

    Shenanigans in Mr.Rogers neighborhood

    Its junk, just send it to me and i will put it out with my junk.;)
  16. xTomKx

    xTomKx Well-Known Member

    When you rebuild the carb there is a small port in the bowl that needs cleaning. That is the source of 90% of the carb issues on those bikes. The factory made the port too small and it easily plugs up. Some people drill them out but micro drill bits are needed. I got tired and upgraded to Mikuni VM24. Runs so much better.
  17. SuddenBraking

    SuddenBraking Well-Known Member

    After I tried to rebuild the original, I replaced with that exact carb (Mikuni VM24).
  18. xTomKx

    xTomKx Well-Known Member

    did you jet the mikuni properly?
  19. SuddenBraking

    SuddenBraking Well-Known Member

    Probably not, although I'm doubtful it's a bad jetting issue. If I had to guess it'd be the carb being installed incorrectly, but TBH I think it's probably the top end. I can't recall what it sounded like when it ran good, but it sure sounded (to my ear) like total dogshit as it idled in that video upthread.

    I'll have Rob from TSP diagnose it and then we'll go from there.
  20. Spang308

    Spang308 Well-Known Member

    Not sure what class you run, but I don't think aftermarket carbs are legal in Stock100. May want to have the original rebuilt.
    Robert is an undisputed expert on those bikes. He'll certainly get it sorted.

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