Engine Trouble MX5 - Where to get information and parts? Leaky head!

Discussion in '2-Stroke Engines' started by boy&hisdogs, Oct 26, 2015.

  1. boy&hisdogs

    boy&hisdogs New Member

    Long story short, an MX5 equipped bike has fallen into my lap and it need some work. Where can I find information (repair manuals, torque specs, carb settings, etc) and/or replacement parts? Google turns up nothing except some very basic sales specs.

    It currently does not run, it came to me with a leak between the head and the top of the cylinder and will not start. If I hold the flywheel at TDC I can hear air escaping and the pressure against my hand dropping until just the weight of my hand makes it spin. Also, the exterior of the motor is all greasy and filthy below the cylinder/head line, but the top (exterior) of the head is relatively clean. I pulled the head off and there is no gasket there. Is this stock/normal? The head nuts look like they had not been tampered with before, at least not by the same drunken ape who stripped all the screws and rounded all the bolts elsewhere on the bike.

    I have a drill press and I'm pretty handy with a jeweler's saw (high-precision coping saw for soft metals) and could easily make my own copper gasket, but would prefer a commercial source if possible. I'd also be interested in any carbs or carb parts that might be available. That's the next hurdle once I get this engine sealed up. I tried fitting a Chinese "high performance" carb (for the common 48/66/80cc chain drive kits) but it was way to large for the MX5's intake. Also, are there other 33cc or really any engines out there that might share parts if I can't get anything MX5 specific?

    Thank you all for your time. I'm not a newb to small engines in general, but I am out-of-the-loop as far as motorized bicycle specific things go.

  2. butre

    butre Well-Known Member

    a little bit of PTFE tape twisted up and laid around the mating surface makes an effective head gasket. try that before you go spending 40 minutes cutting a head gasket with a jeweler's saw.
  3. boy&hisdogs

    boy&hisdogs New Member

    I'm fixing this bike up to sell it, so I don't what to ghetto rig anything. I ended up making a gasket out of .025 aluminum. The smallest piece of copper I could find was about 1x2 feet and was $45, so I went with a smaller $10 piece of aluminum and still have enough for several more. I cut around the outside with a sawzall, drilled the bolt holes on my drill press, then cut the main hole to about 90% size with the jewelers saw (5/0 blade ate through it like butter) and finished with a file, checking it often.

    No more cylinder leak, but the bike still won't start. The carb leaks around the top of the float bowl (maybe elsewhere too) and I'm sure the settings are all out of whack. I bought a tube of "gas resistant" RTV gasket maker/sealer, we'll see if it holds up.

    Nice sig btw butre. That's one of the projects on my list after I get this thing running and sold!
  4. jaguar

    jaguar Well-Known Member

    check for air leaks at the crank seals.
    do you get a nice spark while holding the spark plug against the head?