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Mystery hydro lock

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by jack_1313, Jan 31, 2013.

  1. When I tried to start my Hornet this morning, the starter motor turned for a split second and then "click" - stuck. The engine wouldn't turn over by hand, so I pulled the plugs and, sure enough, cylinder #3 was hydro locked. Ok, problem solved - but what on Earth could have caused the lock to occur sometime between when I parked the bike last night and when I got to it the next morning?

    The vacuum-operated fuel tap is not leaking.
    Cylinder #3 is sparking fine and heating up in sync with the other cylinders.
    The is no sign of coolant entering the combustion chamber - no smoking, and the liquid spat out appeared to be fuel.

    So it's a mystery. Any ideas?

    The only thing that I can think of is that the float in carb #3 is malfunctioning, and the fuel left over in the fuel line was enough to feed in, via gravity, and flood the cylinder. I wish I'd checked the line to see if it was empty when I pulled the tank!
  2. So you're saying it was full of fuel?
  3. Yep, to the extent that the piston was unable to complete its stroke, preventing the engine from turning over.
  4. Float in no 3 carburetor bowl got stuck, didn't close and filled the carburettor and eventually the cylinder?
  5. coolant low ?
  6. oil colour ok ?
    best to eliminate some possibilties
  7. If it was purely fuel, I'd suggest as above with the float in the wrong spot, but it doesn't explain if the fuel tap was off.
  8. You 100% sure it was fuel? Did you drain the cylinder for the 67ml of fuel? You certain the tip of the plug wasn't just a bit wet? I do believe that 250 hornets exhibit that exact symptom on flat battery. Having a battery collapse is far more likely than fuel leaking from nowhere.
  9. If you didn't try and drain the cylinder, turn the engine with the plug out, see if that removes any fuel. Alternatively, set it up in working order and put a pan under the carbs to collect any runaway fuel this time around.
  10. Hey guys, thanks for your insight! The engine was definitely hydro locked - by "pulled the plugs" I meant that I took them out and used the starter motor to spit the fuel out (I should express things more clearly). I then took the bike to uni.

    Of course, when I was done for the day I came back to the bike to find cylinder #3 hydro locked again. Luckily I had anticipated that that might happen and brought the necessary tools with me to pull the plug out. The base problem was a bit more apparent this time though - when I pulled the tank off, petrol was leaking freely from the fuel tap. Yet by the time I got home it had stopped leaking again.

    Thus, the key issues are fairly obvious:
    1. The fuel tap is leaking intermittently. The diaphragm is probably toast.
    2. Float/valve in carb #3 is letting fuel through when it shouldn't. This has probably been the case for a while, but has only become a problem now due to the faulty tap.

    Off to Supercheap tomorrow to get a switch to splice into the fuel line as a temporary fix until I get around to repairing the fuel tap and opening the float bowls.

  11. Sounds like you're on top of the issue.
  12. I was, up until the point where the fuel tap decided to go the other way and stop letting fuel through altogether. It was a long, uphill push to get the machine back to a mate's place.

    Just picked up the rebuild kit, so hopefully no more problems after a bit of work tonight.