maybe someone can shed some light....


4 replies to this topic
  • gbalias

Posted November 15, 2012 - 07:28 PM

#1

buddy got a used 2004 450.


had blown head gasket. we fixed all the normal stuff thats involved. the top end has recently been done by PO. i inspected and verified this. its got a wiseco std bore/comp piston.

reassembled and ready to go.

now, i found it to be strange that it had a 52 pilot jet in it.....OBEMR needle (and i forgot the main jet #)....

ran way lean with the screw at about 2 turns. hanging idle, instant red hot header, sputtering, etc. (im quite familiar with the YZ's as ive had a number of them in the past 400, 426 and now on an 08 450) all the others including mine and another friends 2003, we;re using a 48 PJ at about 2 turns out.

on THIS setup, the one with the 52PJ, it didnt end up running 'normal' until it was a little over 3 turns out.


my question is where is this OBEMR needle from and why so darn rich on the pilot circuit? ive tuned a lot of FCR's in the past as well and nothing ever this rich.

we still have yet to ride it for a shakedown (ie, track, woods, etc.....so far only the street up the block or so.) but i want to be prepared with jets when we do go out.

i was considering putting in a 45 or 48 just to see what was going on.

  • grayracer513

Posted November 16, 2012 - 08:37 AM

#2

The OBEMR needle is the Canadian (AUS, Euro, etc.) spec'd part. The US model had an NCVQ. As built, the CDN carb had a 172 main and a 45 pilot, while the US bikes had a 168/42.

There are probably other differences internally, like the needle jet/main nozzle, but a lot of things can contribute to lean operation in spite of such rich jetting as you have. One is tight intake valves or an intake leak. Intake vacuum at a 2000 rpm idle should be around 8-10 in/hg on a gauge. Cam timing being retarded on the intake side will also lead to similar symptoms.

You could also have a dried varnish deposit in the pilot jet or elsewhere in the circuit. Compressed air and spray carb cleaners won't remove these, usually. A broken or inverted vacuum release plate on the back of the slide will give you trouble as well.

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  • gbalias

Posted November 16, 2012 - 11:12 AM

#3

hmmm...ok...we've determined its a canadian bike. theres some canada stickers on the steering stem along with race 'license' decals matching the numbers on the number plates. who the heck knows how it got way down here...but no sweat.

valves are within spec as we reshimmed everything once we got it back together, then verified the clearances. cam timing is also good. but im still gonna recheck all that.
slide/vacuum plate is good, and i didnt notice any restrictions in any of the carb passages with the ol carb cleaner check. lol.

hot start plunger is good, etc. next step is to verify any intake leaks and go from there.


im thinking to also put the stock jetting from my 08 in there and see what changes. (ive got a JD kit in mine, so the stock stuff is available)

it runs good all around the rest of the throttle, its just this idle thing....i just find it strange it needs 3 turns on a 52 to act like mine with 1.5 turns on a 48. i mean, they cant be all THAT different, right?

  • grayracer513

Posted November 16, 2012 - 03:26 PM

#4

You never know, but how much could it hurt to try it? I'm not up on what the exact difference is between the Nxxx and OBxxx series needles is, but I don't think JD discriminates between US and Canadian models with their kits, so they probably interchange to some degree.

  • gbalias

Posted November 16, 2012 - 06:30 PM

#5

i can only assume its for a richer (relative) mix. seeing as how they are damn near north pole, average ambient temps are probably considerably lower. maybe its to offset that.

but like you said...who knows.

ill throw my stock jetting in there and see. probably wont be till sunday, maybe. depends on this darn house remodel.





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