jetting confusion

5 replies to this topic
  • budweiserfrog

Posted June 18, 2005 - 04:49 AM


I have no experience jetting wise at all.
Having bought a new 04 wr450 with yamaha uk fitted road kit it will not idle and revs on hunting when i want to stop. i have found that it has been down jetted a lot so i have fitted:-
Main jet no 165.
Pilot jet no 48.
Fuel screw 1.75 turns.
also Needle standard & clip position no 4.
Altitude 0-4000ft.
Temperature 70-80.
Now the snap of power is great,
Idle revs steady, couldn't be nicer,
Revs don't hunt anymore,
BUT at a steady rev, especially a low or mid rev it seems to choke up and cough.
If i release throttle it will idle fine & if i increase throttle i need to open it up well to clear the roughness.
There is no popping.
What do i do?
I'm not sure whether to play with the fuel screw or adjust the needle clip position or what? :)

  • Indy_WR450

Posted June 18, 2005 - 04:53 PM


disconnect your TPS at the carb and the problem is solved! :)

  • budweiserfrog

Posted June 18, 2005 - 11:34 PM


:) I've solved it.
When i took the top off the carb i noticed that i'd forgot to put the little grub screw that holds the needle down back in.
It's always the same, you learn by your mistakes.
After a test run it was near perfect.
I raised the needle clip to position 3 & :) .
Thanks Indy for your suggestion, how will the tps disconnected affect my bike?

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  • Indy_WR450

Posted June 19, 2005 - 05:10 AM


Your TPS will act like it is cutting out the ignition at steady 1/4 throttle while you maintain constant speed. Some members like to have a switch added to turn the TPS on and off. TPS plays with timing at low rpm and full throttle technical riding. :)

  • deadcarnahans

Posted June 19, 2005 - 01:16 PM


My bike just purs along fine at any constant throttle setting. Never messed with the TPS, and the book says not to disconnect it. Could you elaborate on this subject some more? Thanks.

Finally drove a KTM 450 the other day. A totally different engine compared to the WR. Smooth as glass, couldn't feel any vibes hardly. I was impressed.

  • Robert_Brazil

Posted June 19, 2005 - 03:38 PM


What is a a TPS,? That black e-connecting plug on the left side of the carb.?Why should one turn that off? Has the YZ has it too


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