Help! 2012 YZ250F jetting issues

[Ando422]

I'll start by making a record of the changes i have made to the bike

FMF 4.1 mega bomb pipe

ported the head

jd jet kit

twin air filter and removed the screen

airforce moto tassinari air boot

currently running a mix of aviation fuel (100LL) and premium 3 gals avgas to 1 gal premium

 

jetting currently

182 mj

RED needle 5th position 

50 leak jet

2 turns on fuel screw

pilot jet unknown at the moment

 

the bike is ridden primarily at 500-1500 feet at 50-80 degrees

 

 

 

My problem is that the bike runs hard at 0-1/8 of throttle (probably pilot) However the BIG issue is that under load (soft sand or g outs or getting close to over rev while airborne) the bike will bog down hard or run really hard and start cutting out.  At a local track this weekend I had the biggest issues when dropping off a single jump to flat bottom.  All last year I had issues with the bike falling flat on its face coming out of corners and bogging out while using the throttle in the air.

Since porting the head this winter I have had to move from a main jet of 185 to 182 and i've changed the accelerator pump screw multiple times and i think its in the most effective position.  Running the bike through the gears and to full throttle the bike feels good its only once on the track during load does it start to have issues.  To be honest all the issues started when i put the Airforce boot on, but I don't want to take it off because it was a lot of money and there is a power gain while its on.  

 

Would a Quickshot 3 be a good idea?  Should I run different gas?  Should I get a different ignition system?

 

Any advise would be great.  My local shop owner is tired of me stopping in every day.  

[ronbuell]

I thought the RED needle was the HIGH Altitude needle.  You said you are at 500-1500.  I used the BLUE needle at that altitude, and mine ran great with settings in the documentation.  Maybe they changes something for 2012, but I'd check the docs and maybe change the needle!

[Ando422]

I tries the blue needle before and it ran really badly from 1/4 to 3/4 throttle.

[SUnruh]

while that is what the docs say, the temps also affect which needle to use.

 

my bike never ran well with the blue, but did with red.

 

either go richer or leaner on the main 1 step at a time

[moleson10]

Stock leak jet is a 90-95. I'm suspicious of the 50 leak jet causing your bog and possibly other problems.

 

The changes you've made, air boot, filter, head porting and muffler should have increased air flow and require richer jetting. But you are leaner than stock on the main 182 vs 185 stock and lean on the needle. At your altitude that doesn't add up.

 

My advice is to go back to stock settings, including the stock needle if you still have it. Replace your pilot jet cause they tend.to clog. The bike should run OK with all the stock setting even with the changes you've made to the motor. Get a good base line and go from there.

[oldnbold]

I'm with sunruh on the needle. The red worked best for me and my red is on 3rd or 2nd from top.

Contrary to popular thought the more airflow you have the LEANER you go on the jets due to more airflow thru the carb "sucks" harder on the jets making rich condition

This is true for all the carb circuits except the leak jet circuit.

I'm at same altitude yet mostly warmer temps with a pipe cam and mild porting

Pump gas

I'm 40 pj

red needle 2nd

185- 180 MJ depending on temp

45 LJ

My bike can easily pull 3rd gear out of almost any corner w/o bogging all the way to the limiter if need be.

The only time I get a bog is after sitting in the heat and 1st lap of another moto It's like the fuel has boiled in the bowl and the LJ has nothing to squirt. It's consistent so I compensate by twisting the throttle hard before getting on the track It only does it the 1st time then I'm good to go.

[Ando422]

Stock leak jet is a 90-95. I'm suspicious of the 50 leak jet causing your bog and possibly other problems.

The changes you've made, air boot, filter, head porting and muffler should have increased air flow and require richer jetting. But you are leaner than stock on the main 182 vs 185 stock and lean on the needle. At your altitude that doesn't add up.

My advice is to go back to stock settings, including the stock needle if you still have it. Replace your pilot jet cause they tend.to clog. The bike should run OK with all the stock setting even with the changes you've made to the motor. Get a good base line and go from there.

You were right it was the leak jet that JD jetting supplied. I don't know why they give you a 50leak jet. Right now I'm at a 182 mj with the stock leak jet and the bike rips again.

[Daniel meyer]

On 5/8/2014 at 9:34 AM, Ando422 said:

I'll start by making a record of the changes i have made to the bike

FMF 4.1 mega bomb pipe

ported the head

jd jet kit

twin air filter and removed the screen

airforce moto tassinari air boot

currently running a mix of aviation fuel (100LL) and premium 3 gals avgas to 1 gal premium

 

jetting currently

182 mj

RED needle 5th position 

50 leak jet

2 turns on fuel screw

pilot jet unknown at the moment

 

the bike is ridden primarily at 500-1500 feet at 50-80 degrees

 

 

 

My problem is that the bike runs hard at 0-1/8 of throttle (probably pilot) However the BIG issue is that under load (soft sand or g outs or getting close to over rev while airborne) the bike will bog down hard or run really hard and start cutting out.  At a local track this weekend I had the biggest issues when dropping off a single jump to flat bottom.  All last year I had issues with the bike falling flat on its face coming out of corners and bogging out while using the throttle in the air.

Since porting the head this winter I have had to move from a main jet of 185 to 182 and i've changed the accelerator pump screw multiple times and i think its in the most effective position.  Running the bike through the gears and to full throttle the bike feels good its only once on the track during load does it start to have issues.  To be honest all the issues started when i put the Airforce boot on, but I don't want to take it off because it was a lot of money and there is a power gain while its on.  

 

Would a Quickshot 3 be a good idea?  Should I run different gas?  Should I get a different ignition system?

 

Any advise would be great.  My local shop owner is tired of me stopping in every day.  

I would try standered needle 5th position 180 main jet a 42 pilot jet and air mixture 2 and a half turns out and oring mod to the exalerator pump