Carb issues? - have searched threads

8 replies to this topic
  • ktmwhore

Posted April 23, 2009 - 01:29 PM


Having a difficulty with this..
06 yz450
sea level to 3000ft
fmf powerbomb, ti-Q muff, uni-filter & notoil
48pj, 170 main, JD blue #4 & zip ty davis mod
Fresh piston, rings, valves, seats & springs
have verified valve timing, have removed carb verified float level, verified clean jets and pilot circuits, etc.(even after zip ty mod)
problem is this; at about 1/8-1/4 throttle (off idle, i guess) there is a hesitation / stammering until you get about 3/8-1/2 throttle where it runs very well. when finally warmed up the engine idles down normally..though it seams slugish to react to pilot screw adjustments, it does respond. i've not detected any vacuum leaks..what is next?

  • Wiz636

Posted April 23, 2009 - 02:41 PM


With that 48 pj you are probably running a little too rich now that the weather is warming up. I would try a 45pj.

  • grayracer513

Posted April 23, 2009 - 03:02 PM


I agree as to the pilot jet. Ordinarily, I'd say the 170 was a little big, too, but the JD needle probably needs that.

As an experiment, disconnect the TPS and run it that way. If it improves, thoroughly test the TPS according to the manual and check the adjustment.

  • ktmwhore

Posted April 27, 2009 - 06:42 AM


thanks guys, i'll try that. really appreciate the help!

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  • ktmwhore

Posted May 06, 2009 - 08:49 AM


still having that heavy stammering/bog/hesitation at part throttle..went to stock 42PJ - no help.. now it just pops on decel like it used too. but it does seem to respond better to fuel screw adjustments (still not what i would expect though) will go to 45pj when this problem gets sorted out. disconnecting TPS did nothing to resolve hesitation..

noticed the following:
when bike is cold and cooler temps around 60 deg there is no hesitation and runs the way one would expect.

after warmed up good, no matter what OAT, the problem returns.

after heavy whoops or a small jump, any situation where negative G's are felt, there is the stammering/bog.

  • grayracer513

Posted May 06, 2009 - 10:53 AM


Check the float level next.

  • GCannon

Posted May 06, 2009 - 11:00 AM


Does Zip Ty mod the AP circut?

  • grayracer513

Posted May 06, 2009 - 11:02 AM


I believe they do the O-ring mod, but no mods to the circuit itself. They modify the main air jet passage and install a new emulsion tube/needle jet.

  • ktmwhore

Posted May 06, 2009 - 11:33 AM


Check the float level next.

have verified the float level is at the .310" dimension.

zip ty mod..heavier spring in ap linkage and emulsion tube

i think i'm going to go back to stock jet and needle just to eliminate those changes..

any other ideas?

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