yz250f rebuild - jetting

[williamson425]

03 yz250f - we just put in a higher compression piston and completely redid the head with new valves, and had the seats machined and all that.. perfect adjustment and so forth. also a jardene (sp?) full pipe put on it.

There is a lag if you pop the throttle.

We raised the needle one spot
bumped the main from 178 to 182
It has a 40 pilot
air screw is 2.25 turns out (stock i think)

Question is.. would putting a 42 pilot in sound unreasonable ?
possibly need a little bigger main as well ?
thoughts on needle position. ?

Pretty soon we are sending the carb to toyko mods but trying to make it usable for now.

 

[rockers109]

What do you mean there's a lag? Does it make a booowahh sound when you go to get on the throttle? Sounds to rich to me.

 

[williamson425]

dead spot .. if you roll it on a bit slower it is ok. if you snap it quick it kinda bogs out then revs

 

[stevena198301]

168 main jet... 42 pilot. Try that one..

 

[SFO]

Check the AP squirt time.
I'd go 1.5~2seconds tops.
A better running engine can generate a stronger intake pulse requiring leaner jetting.
Anytime my yzf bogged it was rich.
not rohrich

 

[Matt90GT]

Yamabog

That is the affectionate name for it.

You are running to rich on the main, lean on the pilot. Also probably lean on the leak jet that is causing the majority of the problem.

Run a 45 pilot, 178 main, play with the needle clip position. Fuel screw should be abotu 1.75 turns out and a #60 leak jet.

 

[RM125Guy]

Hmm i know my jetting is way off from stock but my bike seems to run GREAT someone tell me if something is way off here....it has the stock keihin carb......mods are as follows...twin air filter,hot cams stage 1, all new ti valves,new vertex piston and a new crank, pro circuit ti 4 full exhaust, hmm i think thats it....but messing with the jetting here is what i have right now that is running good...i mean its very strong no lag or anything....185 main,58 pilot, needle on bottom position, and air screw is out 2 1/2 turns leak jet is stock 105 does this seem ok or is the pilot way off? i had a 42 stock thanks ..

 

[BadgerMan]

Fuel screw should be abotu 1.75 turns out and a #60 leak jet.

Yes, swap the #105 leak jet for a #60 or even smaller.