Well I just bought my first 4T an 07 rmz-250 all stock. I have torn it down, checked the valves etc, and these are the jets that are currently in it. It seems to me like the previous owner richened it up. The bike runs ok, no bog really accept when i try a sudden snap off idle it will die/bog unless i release the throttle. The current jets are:

Main: 180
Pilot: 45
Slow???(jet next to the main):75
Leak:40

My friend suggested going to a 55 on the leak jet to help with the bog when snapping the throttle, but is there a better jetting combination i could try out? No popping, no bogging anywhere else other than the one i spoke of. Would the o-ring mod be helpful for the bog? Or are the quick shots a good product to use?

Paczowski123, on 07 February 2012 - 04:09 PM, said:

Congrats on the new bike.

Jetting:
Main: 180
Pilot: 45
Slow air jet : 75
Needle:? (NCVS)
Air jet: ? (use stock)
Leak jet: 40 (too small, go to 50)

Here's the deal: Bog is 100% a function of the Accelerator pump system (assuming the rest of the jetting is correct, and the apump diaphragm is not old and crusty...)
You must determine what is and what isn't working with the apump system. The easiest way to do this is to pull up the subframe exposing the entry to the carb, and watch the apump nozzle work.

1. it should squirt every time, unless you open the throttle veeerrrry slowly.
2. it should squirt all the way into the head, one single straight stream of fuel
3. it should last .8 - 1.2 seconds
4. it should NEVER hit the slide (early) , or be way behind (late) when the slide opens. Any evidence of gas hitting the slide and it will run poorly.

1. if it doesn't, the spray nozzle is clogged. Clear it with solvent type carb cleaner (but keep the slide up, so you won't ruin the slide seal)
2. if it doesn't, the leak is too large (not enough fuel), or it's still partially clogged
3. this should not be a problem if the stock diaphram is used. Do not use older CRF450 diaphragms
4. the adjustment screw for timing is under the black cover on the side of the carb. Clockwise delays the squirt.

Oh, and do all this with the engine off, please. I don't want to see pictures of your gas-burned leg and arms......

Have fun.

haha while i was reading that i was like, wait i do this with the bike running lol...But ok ill check it out. You say the adjustment screw is under the cover, is that the phillips head that presses up against the black lever (the one everyone does the o-ring mod on). Now let me make sure im following you correctly.

Make sure the diaphragm is not old and crusty if it is replace it (do not use crf450r)

The stream should squirt under the carb right into the head as soon as the slide opens (but does not hit the slide if it does turn the adjustment screw counter clockwise to slow timimg)

If it doesnt spray the leak circuit is clogged

(now heres where im confused where you said the leak is too big) you said :"if it doesnt the leak is too big" if it doesnt what? spray all the way into the head or have a strong stream??

Correct on all.

Quick question, where is the air jet on this carb?

And when someone is talking about adjusting the air screw on these fcr carbs which screw is the air screw? Is that the screw on the bottom of the carb? I always thought that was the fuel screw?

Also, when you were listing the jetting underneath my post, were you listing the stock jetting or just verifying what i said? And what does NCVS mean?

Don't change the stock air jet (in the intake bell of the carb).
Pumper carbs have fuel screws, not air screws (on bottom) which you should upgrade, cause you will need to adjust it regularly.
NCVS is the best needle for MX type FCR applications, in most cases like the CRF, YZF, KX. Motors with shorter intake tracts (KTM) like different needles.

Krannie, on 10 February 2012 - 08:44 PM, said:

So are you saying my RMZ does not have a NCVS needle?
I will be upgrading my fuel screw shortly i was thinking of the R&D Flex Jet looks simple to adjust even while sitting on the bike. Any experience w/ this?

Paczowski123, on 12 February 2012 - 10:34 AM, said:

I don't know. I know the Honda CRF450R came stock with the NCVS needle for several years, and it is used by tuners on the YZ, CR, RM, KX, etc, etc.