76 honda 2 stroke help

Discussion in '2 smokers' started by rackdaddy, Feb 27, 2013.

  1. rackdaddy

    rackdaddy Adventurer

    Joined:
    Aug 27, 2011
    Oddometer:
    22
    Location:
    Little Rock AR 72223 (on the way)
    Evening all,

    Rebuilding a 76 Honda Mr 175, I have the machine cranking and running for about 1 min at a time. Very hard to start usaully wheres me out before it cranks over. I get all excited when she fires up then crappes out on me. Rebuilt the carb, cleaned it all out. Had alot of blow-by when i got it. removed head cleaned it all out, fresh oill and gas fuel lines, pet...etc.
    Seems that it dies as soon as it warms up could the crank seals cause this. trying not to open up the crank if its not necessary. If the seals are leaking it isnt very bad.. (not alot of oil buildup underneath)
    Anyone have any EASY ANSWERS. :freaky
    Thanks for any input
    #1
  2. stainlesscycle

    stainlesscycle Long timer

    Joined:
    Jun 6, 2008
    Oddometer:
    2,330
    Location:
    morgantown, wv
    could be low compression. is there lotsa dark spots below the rings on the piston?
    #2
  3. anotherguy

    anotherguy unsympathetic

    Joined:
    Jun 18, 2009
    Oddometer:
    9,077
    Location:
    the hills
    It's 37 years old. There are no easy answers.

    Start with checking the compression. Should be at least 90PSI if not more. Must be at least 60 PSI to support combustion.
    #3
  4. Dave in Wi

    Dave in Wi Long timer

    Joined:
    Feb 25, 2007
    Oddometer:
    2,148
    Location:
    Madison WI (40 Square Miles Surrounded By Reality)
    Hard starting in a 2 stroke can be a symptom of low compression. Leaking seals can show up as uncontrollable high-rpm run-on or lean running due to an air leak, or lots of smoke from the transmission oil being sucked into the crankcase. I'd start by checking the compression. Good luck and let us know what you find.
    #4
  5. Gramp-Z

    Gramp-Z Been here awhile

    Joined:
    May 28, 2009
    Oddometer:
    960
    Location:
    Maple Valley , WA , USA
    I had one years ago , got it for cheap . Didn't run too well . So I rebuilt it and in the process I found somebody's extra strange port job . When I got it all together it still didn't run too well . I finally cut the expansion chamber apart and found some of the baffles had broken loose and was limiting exhaust flow . Welded it all back together and she ran as good as she could with the strange port job . Nothing in the high RPM , but would pull like a four stroke just off idle . If it isn't your crank seals , remove the exhaust and see if there is anything rattling around inside . Good luck !
    #5
  6. mudgepondexpress

    mudgepondexpress Long timer

    Joined:
    Jan 11, 2007
    Oddometer:
    1,206
    Location:
    Spokane, WA
    Same with my old MR175...the pipe was plugged with carbon and the baffle had somewhat come apart. The easy way to clean out the pipe is with 2 feet of wire rope and a drill. Untwist the rope at least 6 nches and then insert in the pipe. Start drilling and moving the rope in and out slowly. This should knock a most of the carbon out. You can shorten the rope as you go along so it is managable as you get near the headpipe.

    Pull the baffle out and soak it in carb cleaner, then rinse with water.

    I hate to say this but the MR was underpowered and overweight. IT's ate my bike for breakfast even when it was running perfect, it was embarassing to own in the 70's.

    Kenny
    #6
  7. Gramp-Z

    Gramp-Z Been here awhile

    Joined:
    May 28, 2009
    Oddometer:
    960
    Location:
    Maple Valley , WA , USA
    This is so true , as on its best day it wouldn't outrun a good 125 . The only place mine would out do almost every other bike was on slimy hill climbs (probably the port job) . Started out naming mine Gohmer Pile , later shortened it to Gomez . Used to unload it from my high trailer by releasing the straps and kicking it off to the ground . Some KTM guys watched me do that one day with their jaws hanging down . A short time later they were trying to get up a nice muddy hill climb without success and I just rode right up like it was no big deal . They looked a bit sad . Also with the air intake under the seat it was great for deep water crossings . It would do a nice 40' crossing up to the top of the forks . I beat that bike and it wouldn't die .
    #7