needle jet and seat on 98' yz400f

3 replies to this topic
  • honda0071

Posted July 10, 2009 - 03:20 PM


i took my bike to shop to get bearings pressed since i dont have a press and i guess they started it and found that it was leaking gas into motor becuz seat and needle is bad... they gave me part number, but i was wondering if this is really the problem..... im guessing the float bowl got stuck now needle and seat are bad or wat? ne suggestions greatly appreciated... and this happens when fuel petcock is in on position....

  • DeeCee

Posted July 10, 2009 - 07:01 PM


Usually a leaking seat also shows up by the overflow from the float bowl leaking gas. You could check the seat by hooking the carburettor up to your gas tank (carburettor not fitted to the bike), turning on the petcock and then seeing if there is any leakage. The problem could also come from an incorrect float bowl setting.

Seems to me your best advice is to strip your carburettor, take out the needle jet assembly and give it a thorough inspection, if OK, refit it and check the float bowl setting.

One quick check on the float valve is to have the carburettor off the bike and have the float bowl removed. Blow down the fuel pipe on the carburettor and move the float valve up. This will let you know if there is a seal, and whether it is a good postive seal. Do not blow hard. The best check is with fuel however, as described above.

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  • honda0071

Posted July 10, 2009 - 10:09 PM


ok ill try it... but ya it was leaking out the float bowl when i got my bike back from my house when i first got it to my new residency... so if it was leaking out the float bowl i need a new needle and seat?

  • DeeCee

Posted July 11, 2009 - 12:17 AM


If you cannot cure the leak by cleaning out the needle jet assembly (and the seat on the housing and covering on the jet look OK), best you replace it.

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