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Jetting after changes - New Setup

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Hello Chaps,

Once more I'm coming here for help from the TT team, hope you guys can help.

I had my bike runnig GREAT, but I'm doing a complete rebuilt and alto taking the opportunity to do a few changes/upgrades. That includes jetting.

Basic details:

1) YZ250F 2007

2) 1500 to 2000Mts altitude, Tropical weather (Kenya, Nairobi) (19 to 33 degrees), controlled humidity (not high uless it rains), Ride on high speed and technical trails and Mx track.

CURRENT SETUP Hot Cams, Scary fast power, MRD Pipe, Factory Red Acc Pump, Stock air filter setup

- Jetting - Fuel Screw 2 1/4 out, Unknown needle (how do I get this?? there's nothing written on it) Needle position 3rd from top to bottom, 175 Main Jet, 70# Leak jet, C32 pilot Jet

UPGRADES

- Added one hole to the Airbox in each side "1 inch diameter

- Twin Air Power Flow

- R&D Power Bowl 2(But didn't install the new Detent spring, shall I??)

- Added the o-ring Mode

- Bought a JD Jetting kit. And now need the help with the Jetting!! :smashpc:

I basically need to know:

How to make sure my squirt is right?

Basis the JD kit It appears to me that I need to run:

- 55# Leak adjustment (This came with the JD kit) (Almost 2 turns out on the Power Bowl)

- 180 Main Jet (Guessing basis JD instructions)

- ???? Turns Out on the fuel screw

- Blue needle on the #4 from top to bottom (maybe I should use the Red given the altitude and temp?)

- Same C32 pilot Jet?

I could do some trial error once the bike is ready, but appreciate your suggestions to make sure it's as close as possible as I will have a brand new engine.

To be clear. Consider myself a newbie on it. If any tutorial on basic questions and answers like the operation of the carb I would love it. Questions like the needle and it's function, how to optimize squirt and tune the leak jet, etc.

Thanks For the help

Edited by danilopucci

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you can look at one of my previous posts,do it just like that and your pilot should be a 42 or 45.use the red[leaner] jd needle.main might need to be a 175,but start with the 180.i use the thicker o-ring and also a good quality fuel[renegade mx-4 oxygenated/leade].that should put you in the ballpark.

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you can look at one of my previous posts,do it just like that and your pilot should be a 42 or 45.use the red[leaner] jd needle.main might need to be a 175,but start with the 180.i use the thicker o-ring and also a good quality fuel[renegade mx-4 oxygenated/leade].that should put you in the ballpark.

Cool,

I left the Pilot and the fuel screw as they were and will adjust once I fire it.

I added the main at 180, the red needle at the 4th place from top to bottom and added the thicker oring.

I installed the Power Bowl and tunned the squirt to be just under a second and present in mid to high acceleration, slightly longer than what it was. I believe it end up being the equivalent of a 60# leak jet.

I will rather be rich than lean on a new engine. in any case I believe the airbox modifications might turn the bike a little leaner as more air is coming through.

Parts coming now, might be able to test soon and post on the details next week.

Intriguing that the JD jet kit comes with a needle and mains but not a needle jet.. does that suggest that the needle jet plays a smaller role on the jetting?

Also, pretty disappointed that stuff like the bowl orings and top don't come with the kit given their price and how important they are (in my mind)

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Do not arbitraialy change the squirt. Set/check the AP timing per the manual. Fine adjust by actual test riding.

There are only two needle jets for the FCR carb, a solid and a perforated one. T4he solid is used with YZ's and delivers higyher high RPM performance, the other is used in the WR's and is geared towards low RPM performanjce.

Rich or lean will not hurt your bike. You can be so lean as for it to not even run and it will not hurt it.

You should not change any jetting until after the bike is test ridden and carefiul notes are made. Then when you make any changes, you make one at a time and retest.

If you have installed a scarynow/powernow device in the carb, you are going to have a tough time jetting it properly and getting the most out of it. Be sure to let everyone know you have it installed BEFORE asking questions. I only happened to notice you mention it in your sig.

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Thanks William for the comments, but maybe you didn't fully read my first post

As I mentioned there, the scary fast power was already there and the bike was properly jetted for it.

The changes that might affect jetting and were installe now are:

- The power bowl

- the twin air power flow

- jd jetting kit

- oring mode

Basis these 4 upgrades I changed the jetting as mentioned above

happy to hear if you have any comments on it

Tks

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