2005 YZ250 jetting questions

O.K guy's what's the best all around jetting specs you have come up with that works great year around in or near the north Georgia area? I currently running #48 pilot #172 main jet and N3CJ jet needle. My air screw ranges 1 1/2 to 2 1/2 turns depending. I still have some more work to do from closed throttle to 1/2 throttle range but the bike is running pretty clean at this time. One question I have is has anyone changed the power jet? Stock is #50. Can't find any info stating when this power jet comes into play. Manual says this circuit is active under 8,500 and 1/2 to full throttle. I know there is a solenoid valve on the carb that controls this circuit. I know it must be determind by throttle poistion due to the carb having a TPS and the pick up coil providing rpm to cdi unit. I guess I would need a tach installed and see at what rpm and throttle postion am at while riding. Is the power jet for hard acceleration only? Is the power jet even worth messing with? Any reason why the 2007 and newer YZ250's have 2 sizes richer on the jet needle? What changed in the engine/pipe to need the richer jet needle. Thanks.

The 06 pipe came in that changes things up a bit - hence necessitating the richer needle jet in 07 as stock. Have heard the 06 bike had the needle supplied with a new bike purchase but not installed. If you're pipe is the 05 you may not have need to try the richer N3EW needle though some have said it's a success.

I believe the N3CJ is leaner than stock. You might try the stocker with a 45 PJ or tweak that air screw. You can never have one jetting setting per year unless you only ride it during one season i.e., summer.

The 06 pipe came in that changes things up a bit - hence necessitating the richer needle jet in 07 as stock. Have heard the 06 bike had the needle supplied with a new bike purchase but not installed. If you're pipe is the 05 you may not have need to try the richer N3EW needle though some have said it's a success.

I believe the N3CJ is leaner than stock. You might try the stocker with a 45 PJ or tweak that air screw. You can never have one jetting setting per year unless you only ride it during one season i.e., summer.

I know it's tuff to come up with a setting that's works all year. Just tied of messing with it as the season changes. I thinking of obtaining another carb and jet it for fall through spring and have and another carb jetted for the hot summer months. Could be as easy changing carb then jets. The N3CJ is one size lenaer jet needle then stock and it really cleaned up my 1/8 to 3/4 throttle running in stock #2 clip position. I going to try the #45 pilot but also might order the N3EK jet needle another size leaner. I don't wan't to start a jetting thread and get way off track here. I would love to find or read more information about the power jet if anybody can provide it. Thanks.

I know it's tuff to come up with a setting that's works all year. Just tied of messing with it as the season changes. I thinking of obtaining another carb and jet it for fall through spring and have and another carb jetted for the hot summer months. Could be as easy changing carb then jets. The N3CJ is one size lenaer jet needle then stock and it really cleaned up my 1/8 to 3/4 throttle running in stock #2 clip position. I going to try the #45 pilot but also might order the N3EK jet needle another size leaner. I don't wan't to start a jetting thread and get way off track here. I would love to find or read more information about the power jet if anybody can provide it. Thanks.

Gotcha. The only changes I make are clip position on the needle (leaner in summer) and a leaner PJ in the summer too. My main is constant at 175. :busted: These changes seem trivial to me as opposed to buying a carb $$$. What would be nice is a detachable fuel line in a length appropriate to a Clarke 3.1 gallon tank. I have to snip mine each time and then install a new line each time the tank comes off.:moon:

FWIW- the last letter in the needle code refers to the needles straight diameter. The 07' and newer needle N3EW is 1 step richer on the straight diameter than the 06' and earlier N3EJ stock needle. N3EK is 1 step leaner than N3EJ, again straight diameter only. The straight diameter affects closed to @ 1/8 throttle, 1 step = @ 1% more or less fuel in this area, after that it's no longer in play as you've moved onto the tapers, so from @ 1/8 on these 3 needles are the same. The 3rd letter in the code refers to the taper starting point, N3C_ is @ 1/2 clip position leaner than N3E_. Clip position has a varied affect throughout the throttle range.

I'll be working on my winter jetting in various areas from Alpharetta to Dawsonville & Commerce, Ga., these next few weeks. (I have not ridden my '06 YZ250 all fall.)

My summer specs, with a very slightly milled & modified head, and 25% V.P. C-12, were a #38 pilot jet, stock needle in 1st or 2nd clip, (have not had time to experiment with other needles yet,) and 172 main, (though I felt I could have gone lower, and wanted to try a 170.)

I don't think I've seen anyone here run a #38 pilot, but my bike finished the Perry Mtn. 24-hour Challenge in AL, with this jetting, last June, (in record heat.) We were running Sunoco 110 straight, for that race, though. I get fantastic bottom-end with this set-up.

I'll be jetting a bit richer before I go to Commerce this weekend, though.

Gotcha. The only changes I make are clip position on the needle (leaner in summer) and a leaner PJ in the summer too. My main is constant at 175. :busted: These changes seem trivial to me as opposed to buying a carb $$$. What would be nice is a detachable fuel line in a length appropriate to a Clarke 3.1 gallon tank. I have to snip mine each time and then install a new line each time the tank comes off.:moon:

I dont undderstand why you have to cut you line everytime the tank comes off? Just woundering:excuseme:

I have to use a utility knife to slit the tubing at each fitting (carb and petcock) to actually remove it. As stubborn and cheap as I am I can't bring myself to buy factory tubing to the tune of $15 and then carve it all up to fit.:busted:

I'll be working on my winter jetting in various areas from Alpharetta to Dawsonville & Commerce, Ga., these next few weeks. (I have not ridden my '06 YZ250 all fall.)

My summer specs, with a very slightly milled & modified head, and 25% V.P. C-12, were a #38 pilot jet, stock needle in 1st or 2nd clip, (have not had time to experiment with other needles yet,) and 172 main, (though I felt I could have gone lower, and wanted to try a 170.)

I don't think I've seen anyone here run a #38 pilot, but my bike finished the Perry Mtn. 24-hour Challenge in AL, with this jetting, last June, (in record heat.) We were running Sunoco 110 straight, for that race, though. I get fantastic bottom-end with this set-up.

I'll be jetting a bit richer before I go to Commerce this weekend, though.

WOW a 38 pilot, i'm considering getting a 42 as i think it going to be about perfect, the beauty with the pilot is ya go leaner until you bog then you go back 1 step richer

The distance between the petcock and carburetor is much much shorter with an aftermarket tank. It carries the fuel lower. I could have simply shortened the stock fuel line but wanted to save that in case I ever wanted to put the stocker back on. I used aftermarket tubing that is slightly smaller diameter than the OEM. It won't just slide off. I prolly bought it one size too small. Just a few more feet of that until I run out.:moon:

I have to use a utility knife to slit the tubing at each fitting (carb and petcock) to actually remove it. As stubborn and cheap as I am I can't bring myself to buy factory tubing to the tune of $15 and then carve it all up to fit.:busted:

I did not know that you had a over sized tank. Kinda makes sence i gess.Or you can get this http://www.cyclegear.com/spgm.cfm?L1=&L2=&L3=&L4=&item=TUC_53-0382_G

I have had my fuel line on and off so many times in the past years and im still using the same peice,LOL

WOW a 38 pilot, i'm considering getting a 42 as i think it going to be about perfect, the beauty with the pilot is ya go leaner until you bog then you go back 1 step richer

his (spydenken's YZ) is slightly-milled, and a milled- or squish adjusted- head always has the tendency to require leaner jetting.

also with race gas, e.g. C12, you would need to lean out too, as mentioned by bruce372 in one of the threads here

his (spydenken's YZ) is slightly-milled, and a milled- or squish adjusted- head always has the tendency to require leaner jetting.

also with race gas, e.g. C12, you would need to lean out too, as mentioned by bruce372 in one of the threads here

I'm not so sure that either the head mod or the fuel require the leaner jetting, but simply allow you to go leaner, thus reaping the benefits of the low-end I enjoy, IMHO.

I've still got plenty of "testing" to do. I've never experienced a 'bog' yet, and I still have ignition timing, a couple of E.G. modified heads, pipe spacers, and a Gnarly pipe to test, yet. I always make sure to only make one change at a time, and ride at least twice after each mod., before the next change.

I sure am enjoying this! And then there is my 125, that I haven't ridden for a very long time.....:moon::busted:

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