1974 MT125 Resurrection

Discussion in '2 smokers' started by woahblackbetty, Mar 6, 2013.

  1. woahblackbetty

    woahblackbetty Adventurer

    Joined:
    Mar 4, 2013
    Oddometer:
    20
    Location:
    SWMO
    G'day,
    Here's a run-down on the resurrection of my 1974 Honda MT125 Enduro.
    When I pulled it home from Conway, MO in March of 2012 it'd been sitting for at least 20 years in a combination of barns, fields, sheds, and driveways. Pretty rough shape to say the least!
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    I took it in trade for working on my mate's CT90 (in the background of this pic)
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    Nice and crusty looking... Actually considering clear-coating over the tank and keeping it looking ratty...
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    The original Keihin carb is junk. Pilot jet bore is stripped out, someone previously monkied with it really badly and it's not usable now.
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    Replaced the original coil with a universal EMGO coil.
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    JB Weld on the underside of the tank to seal it up prior to coating with POR15 tank treatment
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    Stator needed repair. Previous owner had jacked it up while taking the flywheel off by the looks of things.
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    Finally! After years of sitting she fired up again!! And smoked my garage out... No complaints here though!!
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    New Mikuni knockoff from eBay, not bad for $40 shipped and at least I can re-jet this one!
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    Installed new tires (not a fun job!!) Shinko SR244's, a 70% street, 30% dirt tread pattern. Bought them online from bikebandit.com
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    TRAGEDY!! I should have checked the status of the piston first rather than figuring that the compression felt 'good enough'
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    Here's a video of the first run in 30+ years. I edited out the first 35,327 kicks.

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    Dropped the piston and cylinder off to 417 Powersports (Springfield, MO)

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    Just picked up the cylinder and piston from 417Powersports (Springfield, MO). $45 for a rebore? Sounds great to me!!

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    Well after some wrenching to reinstall the top end, and some tinkering with the carb tuning, I think we're close to having some serious fun...

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    I worked up the layout of my current carb mount setup vs the Mikuni M-VM28-200
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    Looks like I'll need to file a little on the holes of that to get the screws to fit. Less than 1mm each side though.
    Is there anywhere here in town that may stock these things? I'd rather not have to wait on shipping from an online vendor.

    Also going to fab a support for the rear of the carb so I can run a Unisock or pod filter of some type. Factory airbox isn't in the greatest condition at all & the hose to connect to that is shot too.

    I mocked up the approximate location of the carb once the Mikuni flange adapter is installed and built a small shelf to support the back of the carburetor. I've got a UniFilter 1.75"x4" single stage filter on it's way.
    The shelf attaches to the cross tube which holds the upper rear engine mounts. It's made out of an old mount for radios in cop cars. Planning on using the holes in it to run a hose clamp or zip ties through to secure the back end of the carb when it's all said and done.
    Side view:
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    Front 3/4 view
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    Rear view showing the mounting screws in relation to the oil reservoir
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    Here's a prime example of failed backyard engineering.
    Due to the disintegration of the stock carb insulator and my swapping carbs I rigged up a solution to attempt to mount the Mikuni onto the cylinder.
    That solution was some heavy walled vinyl tubing and a couple of hose clamps. The tubing fit well onto both the carb and the intake spigot at first but then due to heating it became less of a viable option as you can see:

    The tubing in question, left end attached to the intake, right to the carb
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    Looking at the end that attached to the intake
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    Close up view. See that step in it? That's from the heating of the cylinder and the clamping action of the hose clamp.
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    Now, I know that would work in a pinch if I needed it to get me home and it's all I had but it's not going to work as a long-term solution. Live and learn!

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    The pilot that came in the carb is too lean. It runs best with that jet installed and the air screw all the way in. That jet is un-marked but I believe it's a Mikuni 22.5 as that was the stock pilot jet size for the '78-'79 Yamaha DT125 which this carb was supposedly set up for. The next size up that I have is a Mikuni 27 and it's way too rich.
    The bike will fire up and idle with the 22.5 pilot in and the air screw cranked in but there's no mid/top power at all under load so I assume the needle and main jets are still too rich.
    The needle jet/main jet holder won't accept a stock Mikuni main hex jet. The threads are just slightly different (metric vs SAE?)

    gave the cylinder and head a close inspection with the bike idling. Looks like there's a slight leak at the front of the head/cylinder mating surface. Off to Lowes I go for some .025" copper sheet and then O'Reilly for a can of Spray-A-Gasket...
    Here's what I found when I popped the head... Definite blow-out
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    Copper sheet from Lowes
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    Copper gasket spray
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    In process:
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    Finished product
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    The stock MT125 gasket is .050" thick. The CR125 gasket fits also and it's .020" thick. The sheet I got from Lowes is .025" thick so it should work out just fine!
    While I was waiting for the copper spray to set up on the HG I popped the exhaust sealing ring off, wrapped some copper wire around the pipe to force a tighter seal, then popped the pipe back on. It took a bit of light tapping with the hammer to get it to fit in properly and then I took it up the street a couple of houses to see if the HG and exhaust seal helped. No appreciable difference so I pulled back into the garage to think things over.
    On a whim I pulled the cleanout plate from the spark arrester:
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    Then took it for a run up the street... HOLY COW what a difference!! She ran like a scalded ape. Having discovered that I took a coat hanger and ran that up the tail pipe to knock crud loose, then I ran it up through the cleanout port and knocked more stuff loose. Did that a few times and then the cleaning proceedure listed in the manual "open cleanout, block tail pipe with a rag, rev engine several times to blow carbon out of spark arrester"
    Put everything back together, grabbed my helmet and hit the neighborhood.

    I put in a 5 mile jaunt. Due to gearing it's a stretch to get her over 45-50mph but for running around town it'll be great. Definitely a blast to ride, very agile & maneuverable, noisy, rusty, smelly, and in a word "BEAUTIFUL"

    Had an issue come up with the fuel tank lining that I did. Looks like it didn't take properly and there's a good size piece has blistered up from the wall of the tank. Working with POR15 to try and figure out the best fix. Will probably have to strip ALL the liner out and reseal

    I contacted POR15 simply to find out what the required process would be to correct this issue. I was figuring on taking a while, saving some green and re-coating when I had a chance.
    Then the UPS guy stopped by to drop off the new front tire for the Nighthawk. He also dropped this off!
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    Completely free of charge!
    #1
  2. bobfab

    bobfab Long timer

    Joined:
    May 11, 2009
    Oddometer:
    1,738
    Location:
    Westminster CO
    id like to do a old honda 2t resurrection someday, im in :lurk

    I also bought a replacement clone carb for my 1976 DT125. Looked identical to the one you posted above!
    #2
  3. woahblackbetty

    woahblackbetty Adventurer

    Joined:
    Mar 4, 2013
    Oddometer:
    20
    Location:
    SWMO
    I'd be really keen to hear any input you might have on jetting of that carb you've got. As I mentioned, mine seems to be somewhat of a hybrid where the jets are concerned!
    #3
  4. bobfab

    bobfab Long timer

    Joined:
    May 11, 2009
    Oddometer:
    1,738
    Location:
    Westminster CO
    unfortunately i dont think i will be of much help there, the bike is long since sold. Good luck!
    #4
  5. woahblackbetty

    woahblackbetty Adventurer

    Joined:
    Mar 4, 2013
    Oddometer:
    20
    Location:
    SWMO
    No sweat! Thanks
    #5
  6. Highside>Lowside

    Highside>Lowside Hairier Than Thou

    Joined:
    Mar 27, 2010
    Oddometer:
    1,085
    Location:
    ChiTown
    My Firstest Ever For Real Motorcycle was a '74 MT125. I rode the snot outta that thing. The only thing that ever stopped it was deep water.
    #6
  7. Vince

    Vince Been here awhile

    Joined:
    Oct 1, 2006
    Oddometer:
    475
    Same here,I couldnt even ride a geared bike.Had to get it delivered in a truck.Been a while,About 39years ago.
    #7
  8. woahblackbetty

    woahblackbetty Adventurer

    Joined:
    Mar 4, 2013
    Oddometer:
    20
    Location:
    SWMO
    Took the old girl out to a meet this past weekend.
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    #8
  9. smokin2stroke

    smokin2stroke Adventurer

    Joined:
    Mar 10, 2013
    Oddometer:
    18
    So how many heads turned when you wheeled that thing in? My 2 strokes generally bring around a few reliving their childhood. :thumb
    #9
  10. woahblackbetty

    woahblackbetty Adventurer

    Joined:
    Mar 4, 2013
    Oddometer:
    20
    Location:
    SWMO
    Always draws a crowd! Partly due to the rat look, partly because I have the exhaust cleanout removed so it's LOUD, and partly because it's a vintage smoker and everyone has a story about theirs from back in the day...
    The group I ride with are vintage & cafe guys so the old MT fits in really well.
    #10
  11. mortimer

    mortimer Been here awhile

    Joined:
    May 7, 2013
    Oddometer:
    144
    Location:
    east sf bay
    Recently acquired a 75 mt125 for my girlfriend, been having a blast with it, thanks for the writeup.

    Be curious to know if you ever get the carb jetting dialed in - keep us posted.

    :clap
    #11