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  1. #1

    Quick First Start Questions and Problems...

    I started my 750 engine today for the first time after its overhaul. Carbs were for a 650 and way out of whack anyways, so i was concerned about it being wayyy off there.
    No fuel in the lines or pump, so it was a rough start but i got it going and let off the throttle, it ran at a healthy idle for a sec or two then started to ramp up to damn near full throttle, even though i was off the gas. Right when it started to sound like it was revving by itself, i held the stop button, and it kept on revving, so i pulled the lanyard and killed the fuel and it sounded like it was at WOT. It maintained this for about a second or two and i was getting worried and pulled the spark plug wires, all 3 and it kept running... It went for 5ish seconds with no spark.

    What the hell is that?!

    I came back 30 mins later and got the hose ready to try and get it to idle. I turned the idle adjustment out 2-3 turns from where it was on my 650, to try and starve the thing of air at least so it cant rev if it decides to. I cranked it and it started right up and i turned the hose on. After about 2-3 seconds of idle it started to rev slowly again, except this time the stop button worked.

    Now, i found out one of the heads is the wrong one and had 150 psi in one cyl and 120 in the other two, so that could be detonation from high compression? Pop off is set to about 12-13 psi. Im thinking thats why its revving?

    I have a video... Uploading now.
    Last edited by ZOMGVTEK; 07-22-2008 at 09:13 PM.


  2. #2
    seaobin's Avatar
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    sounds like an air leak

  3. #3
    Click avatar for tech links/info, donation request K447's Avatar
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    If you have a choke, pulling it will reduce air flow, should get the RPMs to drop next time.

    Sounds like it was dieseling before you pulled the plug wires. The stop button might actually have worked and shut off spark, but the engine wasn't needing spark to keep running. Finally ran out of fuel and stopped.
    Do you have the correct spark plug heat range installed?

    Are you sure the throttle plates are closing properly? No binding when you let off the throttle lever? Spring return working t close the throttle plates?

    If the throttle is not opening by itself, then you may well have an air leak into the crankcase - crank seals or intake gaskets. Are the carbs dribbling fuel at idle?

  4. #4


    There is the video.. I put a good bit of fogging oil in each cyl before cranking, and sprayed a little in the carb before each attempted start. It might be flammable? But, wow...

    And a air leak is bad, that better not be it. Give me something thats wrong besides a crank air leak.

  5. #5
    bump for WTF!?!? and my odd sounding drunk voice.

  6. #6
    Quote Originally Posted by K447 View Post
    If you have a choke, pulling it will reduce air flow, should get the RPMs to drop next time.

    Sounds like it was dieseling before you pulled the plug wires. The stop button might actually have worked and shut off spark, but the engine wasn't needing spark to keep running. Finally ran out of fuel and stopped.
    Do you have the correct spark plug heat range installed?

    Are you sure the throttle plates are closing properly? No binding when you let off the throttle lever? Spring return working t close the throttle plates?

    If the throttle is not opening by itself, then you may well have an air leak into the crankcase - crank seals or intake gaskets. Are the carbs dribbling fuel at idle?
    Where the carb sits now, its damn near fully closed when you dont touch the throttle, and i didnt touch the throttle after it started running, it did all of it on its own. Im running BR8ES plugs, brand new. Im sure there was alot of oil and assorted possible flammable fluids in the crankcase before this run, its the first time it actually ran. The carb is opening and closing properly and smoothly.

    I cant have it running long enough to see if the carbs are dribbleing fuel, im assuming you would be able to see it looking down the carb?

    I dont see how i could have a air leak this bad... Isnt it a hardcore leak for it to go WOT by itself?

  7. #7
    ph2ocraft's Avatar
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    WELCOME to the Death Rev. Glow Plugging can and will also occur with a lean running condition, things get wayyy to hot, the plug acts like a glow plug and away she revs, no spark needed. Gotta love a diesel.

    If it starts to get away next time prime the crap out of it or pull the choke to introduce more fuel/less air. Keep the idle low and chances of a runaway are slim.
    Last edited by ph2ocraft; 07-23-2008 at 12:37 AM.

  8. #8
    Well i dont know what the idle is, it never ran before...

    I just want to make sure the engine is running alright-ish so i can drive the hour it takes to get to water and break it in and tune the carb a bit..

    Right now i have no idea what the idle is, but the carb looks closed from the top, no real gap at idle, and it runs. I took the 150psi head off, so i cant run it until i get the right one.

  9. #9
    If i need to pull the engine again to fix some air leak im going to be pissed.

  10. #10
    Quote Originally Posted by ZOMGVTEK View Post
    If i need to pull the engine again to fix some air leak im going to be pissed.
    me too, mister i dont lift my own engine.

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