98 won't idle

7 replies to this topic
  • grnrex

Posted June 18, 2005 - 06:53 AM


I just bought a 98 wr400 that was built up for racing and it's got all the power in the world but it won't idle except when cold with the choke on. Any guidance would be appreciated.

  • MN_Kevin

Posted June 18, 2005 - 11:56 AM


Your fuel screw and idle setting...

  • Dirt_rebel

Posted June 18, 2005 - 01:30 PM


check ur carb pilot circuit..(fuel screw, idle screw n pilot jet)..oso check ur air-cleaner, make sure they're clean..

  • MN_Kevin

Posted June 19, 2005 - 03:44 AM


if you decide to open up your carb, there are two air jets that are prone to clog w/ oil from a freshly oiled filter.

These would be the Pilot Air Jet &
Main air jet.

They are inside the air horm on the airbox end of your carb.

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  • grnrex

Posted June 19, 2005 - 05:44 AM


Thanks for the info, I think I'll look at ripping the carb out this next week and check both jets.

  • tcmII

Posted June 22, 2005 - 01:33 PM


If you are getting into the carb, make sure that you check the accel pump too. It won't effect the idle, but the shaft is prone to corrosion and the diaphram collects dirt. Both of these result in a shot shot.

And, as everyone knows, no one whats a shot shot> :)

  • MN_Kevin

Posted June 22, 2005 - 03:09 PM


Speaking of the AP, the 98 / 99's use either the Taffy Mod (less intrusive) or my KL Mod to limit diaphragm pump stroke. Stock, the stoke is ~ 4 seconds. 0.5 has been recommended by a Yamaha Pro Mechanic (the BK [ Brian ???] mod).

But something that could change the results is a power now installed. I don't know if it would help or hurt w/ such a long squirt duration...

  • dkwok

Posted June 24, 2005 - 02:15 PM


maybe the carb slide is cracked???
better open up the carb b4 something serious happen,


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