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loss of power

Discussion in 'Technical and Troubleshooting Torque' started by DillanDog, Mar 6, 2007.

  1. I recently bought a wrong spark plug for my 2-stroke Aprilia 125. It was a grade 6 plug and it should have been a 10. Consequently it burned right to the threads. I replaced the plug with the right one. The top of the piston looks ok, looking down the hole, but the bike is not performing well in the power band. It struggles, like its swallowing chunks of air instead of petrol. Its a 2-stroke and I had it for 3 weeks, so its hard for me to comment on the normallity of the engine noise, but it doesnt seem right.
    Did 4000 km service and they said the compression was fine.
    If the piston, the head, or the cylinder got damaged would that affect the compression?
    Its not cheap to start taking the head of, but if I did it I would not know what I'm looking at rally.
    Any help is gratly appreciated.

  2. Some plugs the lower the number, the hotter, others it's the other way around.

    If it was a colder plug, you may have coked up the combustion chamber, so you may now have poor combustion and hot spots.

    Alternatively you may have other problems that are just a coincident like carby problems
  3. was the service before or after ya fragged the plug into fubarland ?
  4. It was after the service.
    Spoke to another mechanic today. He wasnts $300 for head inspection/work and its $500 for top and bottom if need be. Plus parts of course.
    Its most likely the power valve, he reckons.
    Also 2-strokes apparently drink petrol and eat pistons he says. And here I go picking a relatively newish bike with low K's so I can have a peace of mind in tearms of engine work, over say a '93 CBR250RR. :roll:
  5. I say powervalve is a likely culprit, or the powervalve motor.

    Hope it is motor, and not the valve being broken. RGV's are good at eating them.
  6. What he said, Pull ya power valves out and have a look.
  7. Amusing you purchased an Italian 2-stroke over a Honda for 'peace of mind'. Live and learn.

    If the plug caused a problem, it will be damage to the piston crown (though usually this is catastrophic and you KNOW you have a big problem). But it should be able to be checked by simply pulling the head off and looking: hardly a $300 job. More like $50.

    Also, 90% of 2-strokes are traded in when the owner realises how much the major service is going to cost. back when RGVs were plentiful, every dealer had one with 19,000km on, because the 20,000 service was a full engine rebuild and people just got rid of their bike.

    But 2-strokes are quite easy to work on so if you feel inclined, get in there and have a go.