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leak jet question

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I have been reading alot of posts, I am finding alot of people with the 05 yz250f like mine have been leaning out the jetting specs then running a lot more richer leak jet? :thumbsup: I have read alot and everything says the the smaller the leak jet number the more fuel is flowed ie it is richer. and on PC's web site they stay with the #90. how can you go all the way down to a #40 leak jet and not be floding it out? please someone help. my ap squit is very nice and lasts about .5 seconds no dribble. alot of posts say this is perfect. help help help

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If the bike bogs on the AP squirt and a smaller leak jet helps (by lengthening the squirt duration), then the bike simply needs a smaller leak jet.

If you think about it, it makes a lot of sense. If you lean the pilot/main/needle jetting, then the engine will have less fuel in the air/fuel mixture off-idle than it previously did. When you crack the throttle quickly, the a/f ratio goes way lean and the previously correct AP squirt is no longer adequate to properly richen the mixture.

I have an '07 WR250F. In my case, I went fatter on the pilot and main, but only because I replaced the exhaust and throttle stop, did a bunch of mods and am moving a lot more air than the stock bike did. When I crank in a bunch of throttle quickly, the a/f ratio goes leaner compared to how lean it used to go until the air velocity picks back up enough to bring more fuel through the pilot and emulsion tube and puts the a/f ratio back in the best power range.

The carb is well tuned for power now, has the o-ring mod, and still has a slight bog when I gas it hard near idle while riding the bike. The bog improved a lot when I went from the stock #90 LJ to a #70, but it's still not gone. I'm expecting that the bog will disappear with a #60 or #50 LJ.

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NIce video what one do you prefer to use or does others in here like to use ?

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#60 through #40 seems common here. It depends on what you're doing with the bike and your riding style.

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I'm having a moderatly bad stumble from the off idle position while in any gear on my 05 DRZ sm . Got the sudco FCR kitted carb & have it set to 'Burned's' rec . Removed the pilot air jet (runs real crappy with it in) as per rec thread . Pilot jet = 45 , main = 160 , emn needle clip pos @ middle groove (runs the same @ 3rd groove), 200 main jet . I ride @ generally 500' to 4500' elevation and it does the same thing at all elevations . Tried adj pilot screw @ all positions & seems to work best @ 1 turn out . Was given a rec from a competant mech friend that said to change the leak jet to a couple sizes richer then swap the pilot jet to a 42 . Whatta y'all think ? do it or does someone out there have the answer ? By the way , mods include the above carb , Yoshi rs2 complete exh sys , & uni air filter . What is the stock leak jet for that carb by the way ?

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Hi gravityjunkie,

The LJ and PJ are separate circuits. You can somewhat mask a wrong LJ with a rich PJ, but you wind up rich on the needle. That may actually be your case, I'd need to know a bit more:

1T on the fuelscrew seems a bit low. Is that at the lean peak or to the rich side of the peak? Removing the PAJ is correct. Since you're at 1T, going to a 42 PJ would put the fuelscrew at about 0T which is wrong because you wouldn't be able to lean the pilot circuit at higher elevations.

The 200 MJ sounds rich, and I'm a little confused. Do you use the 160 or the 200? or do you mean the MAJ is 200? (<== should be the case) How does the bike run at WOT.

I don't know the stock LJ size.

Do you get the off-idle stumble when you roll-on power or when you crank the throttle hard? A stumble is usually associated with a rich condition and a bog with a lean condition. If it's a stumble and not a bog, you're too rich on the needle and/or your AP squirt is too long.

I set my carbs up in this order:

MJ: 1 size smaller than what causes a rich stumble at WOT.

PJ: Whatever size gets me to about 1.5 - 2T on the fuelscrew when I'm at the lean peak. FS set just barely to the rich side of the peak.

Needle: best response and power from 1/4 - 3/4 throttle.

AP: shortest squirt duration that eliminates the off-idle bog.

I'll check back on this thread some time in the late morning (pacific time).

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Hehe, I should remember the simple things and not post after a 14-hour day. Thanks for the follow-up Eddie.

-Dave

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Hi Y'all. Thnx for the responses . !st, to answer the questions , sorry bout the typo on the Main AIR Jet - it's a 200 . Main Jet is the req 160 . The stumble happens when rolling off then rolling back on while in any gear . I'll try adjusting the needle leaner as you suggested and also the 'O' ring mod to the ap linkage as per Eddie's suggestion. The only thing is I haven't a clue as to how to do the o-ring mod . This is the 1st I've heard of it . Is there a thread on it or can someone 'splain' it to me if it's not to much a bother . Thanx again guy's for all your help . This place 'rocks' .

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I think I found the ap o-ring mod info in the How To Guide , "Professer Redbeard450's AP Mod". Does all the specs apply to my FCR MX carb too?

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Does anyone know what size the 'O' ring is,I would like to buy

some but the guy at my local shop doesn't know anything about it.

Thanks,

DFS

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I think I found the ap o-ring mod info in the How To Guide , "Professer Redbeard450's AP Mod". Does all the specs apply to my FCR MX carb too?

I'm pretty sure that Eddie would say "Install the o-ring and go ride the bike", but don't quote me on that... :busted:

I'll suggest that though. :thumbsup:

1) Take the throttle cable cover off of the carb

2) Slip the o-ring over the AP lever spring and and stretch it over the AP cam so that it holds the AP cam against the AP lever screw

3) Put the throttle cable cover back on the carb

4) Ride the bike and grin :thumbsup:

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Does anyone know what size the 'O' ring is,I would like to buy some but the guy at my local shop doesn't know anything about it.

5mm - 6mm (about 3/16 inch) - the smallest i.d. that will fit over the spring.

A 6mm fits on pretty easily and still holds the cam decently.

A 5mm is a tight fit over the spring, but probably works a little bit better.

There are handy kits you can get for a few dollars that will last you forever if you want to go that route.

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