98 yz400f wont start.

1 reply to this topic
  • jasonstowe

Posted February 06, 2009 - 09:25 AM


I bought this bike and it had a blown head gasket. So i removed the head and resurface it and adjusted my valves. installed it back on the bike by the book. The bike started and ran for about 2 seconds then gut off. It did that a couple of times. So i went through the carb and cleaned it up. And it still is doing the same thing. I also checked the vent tubes to check and make sure it wasn't vaperlocking. It's got good spark and plenty of gas. Could it be the throttle position sensor? the book had me check ohms between the green and black wires on the throttle position sensor and it should be between 4 and 6 ohms. it was at 4.36ohms. what about timing? the book had me face the cams opposite of one another with the dots on the cam gears at 9 12 3 with the exhaust cam gear 9 oclock dot in line with the head surface. and the intake cam gear 3 oclock at the head surface. and the crank with the "I" in line. Help please.!!!!!!!!!!! :)

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  • grayracer513

Posted February 06, 2009 - 09:35 AM


Your engine needs three things in order to run:

  • Spark at the right time
  • Compression
  • Fuel

Start by narrowing down to what it's missing.

  • Check the cam timing, and while you're at it, check that the TDC mark on the flywheel is actually at TDC. Do this by lining up the I while probing through the spark plug hole for the piston.
  • Check for spark.
  • Check for fuel in the float bowl.

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