All 2st WHY CHANGE FROM MIKUNI TMX38

WRONG you have that backwards. The PWK has a AIR SCREW not FUEL MIXURE SCREW. So the further out you get on air screw the leaner the mixture. The more in you go the richer the mixture.

If you had the old 125 with a TMX and not the TMXX Id say switch to the PWK with a 250 Id say if you want more bottom end and maybe lose a little top end then go with a PWK .
If you are a trail rider or do more technical riding then the PWK - if you do motocross - Mikuni.

I am not a big fan of the JD needles and maybe you could try original specs - and start from scratch . Ive never seen anyone with JD needle in a Mikuni.

Isn't that what John just said without saying richer or leaner?

No, he had it backwards. Think about it.

My 2008 cr 144 with tmx works great on motocross track now. Just took a little jetting might need a little ajustment if there is a big temp change.

Thanks Vinduro I didn't know the two carbs were different in that way. I just wrote down what I read on the jetting section in TT.

It was part my fault. I wrote that my airscrew was unresponsive clear out to 2 3/4 turns and I changed the pilot and it fell in the middle without specifying wether it was rich or lean so I think I misled you, sorry about that. Backing out the air screw gives the mixture more air, going to a larger pilot# gives it more fuel.

Ok thanks Guy's

On BOTH carbs. A 4 stroke carb usually has a fuel mixture screw instead of a air mixture screw. The way to tell which it is is position of the screw. Air mixture screws are always on the back side of the carb, usually on the side. Fuel mixture screws are toward the front . Usually underneath.

Humm... thanks learn something everyday. Now I need to go out to the garage and look at the CR144 and 2010 Husky TC250 to put it all together. Good info.

My Bike was tuned by a mate who is a pro superbike racer, he also owns a 2010 WR300. My bike is a 2008 WR250 which produced more power on the dyno, than my mates 2010 WR300. However, my bike rides like an MX 250 being a real difficult bike to ride on tight slow tracks.

Bike will run all day WOT, but on the tight stuff it will foul plugs. The slide I am currently running is for the polution gear, and the bike has no polution gear fitted. I am about to retune the bike with the carb TMX38 from a 2010 WR300.

The carb on the 2008 model has different internals. Well, I'm sure I will be on the money, with a new carb and #5, #7 slides to play with.

I will post an up date once bike has been retuned

Regards