Recent content by Mammoth

  1. Mammoth

    GX390 Build

    Im learning just like everyone else. I have smart friends and a pile of books that help me build things. The best thing to do is get the engine breathing. The stock carb that comes with these engines is a restriction. Get a motorcycle carb. I like Dellorto they flow better than most and are...
  2. Mammoth

    GX390 Build

    Been consumed by work seven days a week for a month so I haven't had time for anything extra. I did take possession of the boat which took longer to receive than expected, but none the less it did arrive all in order. After looking over the pieces and all the work put into the kit I'd say its a...
  3. Mammoth

    My Weird obsession with stupid chinese four wheelers

    I share the same feeling with the early 1980's honda trx125. They are little pack mules and fun to ride with bigger tires. Im up to three of them. I learned a long ago that little is better for tight trails.
  4. Mammoth

    GX390 Build

    I have a coupler that will connect the 1" shaft to the transmission, and after that it will have a drive shaft to a propeller. Im going to try to increase the efficiency by not running a jet and go with a propeller built into a tunnel. The tunnel is going to be more of an arch. After...
  5. Mammoth

    GX390 Build

    To make a long story short bypassing all the failed ideas and get right to the point after weeks and dozens of attempts the engine finally fired up today. I had installed a new magnet to where I thought it would be, but it wouldn't fire. Had an electrical engineer show up today with all his...
  6. Mammoth

    GX390 Build

    This video has lots of good info about bore vs stroke.
  7. Mammoth

    GX390 Build

    Got the engine all back together and it turns over alot smoother now. Still doesn't fire correctly, but I may have found an answer. I'm thinking the magnet on the flywheel I'm using to trigger the pickup is too long. The instructions call for a 3/8" round magnet. I think the long bar magnet on...
  8. Mammoth

    GX390 Build

    While turning it over on the dyno it seems like its having ignition issues. Can't quite figure it out. The instructions say to set it at 18* before top, but it acts like its firing too early. I tried at 18, 9, 2, then went past top and tried 5, 10, 15, then 20. It fired a few times in a row at...
  9. Mammoth

    GX390 Build

    I see. The transformer still needs 100 amps to operate the welder at max 50 amps. I had to find a solution for the size of the cable going to the welder. A 100 amp 240 volt cable is prety big with screw in connections. By going through the transformer I can now plug it into a regular 50 amp...
  10. Mammoth

    GX390 Build

    I ended up ordering two individual bearings in ceramic for the side cover purchased through CBR Bearing. I will pm you about the snowmobile. Once I make real progress on that project I will start a thread on it.
  11. Mammoth

    GX390 Build

    When your racing every gain in percent counts. After a number of laps the first and second place finishers are usually right next to each other. That means the race was won by a fraction of a percent. Ive never had any negative side effects from thinning the dipper. You can picture how little...
  12. Mammoth

    GX390 Build

    It will go in an aluminum mini jet boat hull. Most people use a jet ski engine, but they use 2.5 gallons or more of gas an hour. Im going to build this boat for long rang. A stock 390 uses just under 1 gallon an hour. This is what I have in mind.
  13. Mammoth

    GX390 Build

    Spent the last three days getting the dyno ready and the engine mounted. Still have a few things to do before testing.
  14. Mammoth

    GX390 Build

    Learning as I go with lots of books for reference. Picking up tons of info on boat design. A lifetime could be spent studying propeller shape. It would be suicidal to the health of your fingers if you put them in the holes of the pull start handle. The plan is just to wrap my fingers around the...
  15. Mammoth

    GX390 Build

    Still going on this pushing it as much as i can, but progress is slow and hard won. Added a tach.
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