Re-Jetting 08 CRF250

10 replies to this topic
  • grantmotox

Posted March 12, 2008 - 12:36 PM


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


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


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

  • Drehwurm

Posted March 13, 2008 - 11:28 AM


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).


  • nzmech

Posted March 13, 2008 - 03:05 PM


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

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • grantmotox

Posted March 13, 2008 - 04:24 PM


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


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


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


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


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


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

Related Content


Jetting by Jensen333

Dirt Bike   Dirt Bike Technical Forums   Intake - Jetting / Fuel Injection
  • 4 replies

Cylinder skirts by Jensen333

Dirt Bike   Make / Model Specific   Honda   CRF250R
  • 3 replies

Honda CRF250R 2016 by zing

Honda CRF250R 2016
  • * * * * -
  • 4 reviews
  • Last review by Jean Lucas
  • On September 10, 2016

Honda Crf250x mods by Son_of_harry14

Dirt Bike   Make / Model Specific   Honda   CRF250X
  • 6 replies

Is it worth it? (Cam and High compression piston) by macgi77

Dirt Bike   Make / Model Specific   Honda   CRF 150/230 F/L
  • Hot  36 replies

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.