Re-Jetting 08 CRF250


10 replies to this topic
  • grantmotox

Posted March 12, 2008 - 12:36 PM

#1

Ok, i tried posting this in Jetting forum and didnt get much help.

i have an 08 CRF250, Fitted a set of Akrapovics on it, everything else is standard, it seems a bit flat on the top end, what you suggest?

Iam at sea level, 0-30 degrees c

  • oabike

Posted March 12, 2008 - 06:29 PM

#2

I've done a lot of dyno runs with a gas analyser and this is what I have come up with. On top the U.S. bike is supplied with a 188 main. It is very rich. For more horsepower and better throttle response I use a 172 main on days over 60 deg F. When the temp drops into the low 50's I run a 175. The carb seems to be finicky in the cold so go bigger (175-180) when the temp drops. I also run a bigger main (175-180) when the track is disc'd really deep,muddy or sandy. On pump gas in the U.S. the bike can run in the safe zone with a main jet as small as 168.

The mid-range is also rich. I drop the needle from the 3rd to the 2nd clip. Honda race techs here recommend the NMUU needle on the 2nd clip. The poor mans solution is to use a half-clip (washer/spacer) and run the stock needle at 1-1/2. The pilot circuit seems OK. Maybe a little rich but the oversize carb doesn't like to go below the 42 pilot so leave it be. The accelerator pump circuit is very lean. You can use a 40-50 leak jet or a MERGE ALJ to fine tune this circuit. I run the MERGE at 3/8 to 5/8 turns out. That is equal to a very small leak jet. My throttle response is very crisp and it never bogs.

  • grantmotox

Posted March 13, 2008 - 10:26 AM

#3

My bike, which was imported into the UK,
Has a #178 main stock...

  • Drehwurm

Posted March 13, 2008 - 11:28 AM

#4

My bike, which was imported into the UK,
Has a #178 main stock...


It has also a richer needle - NMTT ! This is smaler on the straight diameter (richer down low) and one clip richer on the clip position. NMT*#3 = NMU*'4

I have a Euro-spec bike also (do we get different, 96dB, exhausts ?) and currently run 178 main, NMUU#3, 42 pilot, R&D power bowl with ALJ 1 3/4 turns (= 50 leak jet).

Michael

  • nzmech

Posted March 13, 2008 - 03:05 PM

#5

On our 08s here (and 07s) the accelerator pump cam doesnt complete the lift from about half through to full throttle resulting in a bog if the throttle is snapped open to fast in this range. Reshape the cam so there is 3mm lift throughout the entire duration. I am running a 175 main, std pilot,needle & clip pos, & a 55 leak jet over here in nz in 25C & below

  • grantmotox

Posted March 13, 2008 - 04:24 PM

#6

do you feel the difference with the smaller leak jets ?

also, you say your runninh a 175 main, is that with stock pipes?

  • nzmech

Posted March 13, 2008 - 04:34 PM

#7

do you feel the difference with the smaller leak jets ?

also, you say your runninh a 175 main, is that with stock pipes?


Yeah sorry that is with stock pipes, and with the mods you cannot bog the thing on the track..

  • grantmotox

Posted March 29, 2008 - 09:20 AM

#8

i tried a #180 Main and it was worse, got sum stutter when hitting the higher rev range.

also got a #60 Leak jet but havent got round to fitting it yet

  • Exision

Posted March 29, 2008 - 11:51 AM

#9

I´m at the same height and humidity as u.
I run a 180 main, HGS exhaust and have a twinair net and over filter around my airfilter.
Runs good, good response/no bog lots a power

  • grantmotox

Posted March 29, 2008 - 12:51 PM

#10

weird how the 180 made my bike stutter and sort of bog in the higher rev range really.

  • grantmotox

Posted March 30, 2008 - 07:29 AM

#11

been told to richen up the piolet and lean out the main a bit more





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