Yz250 jetting for woods

Yz250 jetting for woods DEFAULT


Originally Posted by bykeView Post

2SYS will probably have some specific jetting info,

Come Byke, we know you know YZ250's too! Will be fun subject to discuss with 2SYS!

James -

To start with, you have your airscrew analysis backwards (you are thinking of it like a fuel screw on fourstroke). If its only 1/4 turn out you need to go richer on your pilot, not leaner. As you unscrew a two stroke airscrew it leans the mixture unlike a 4T fuelscrew that is adding fuel. So if anything, you need to go richer on your pilot.

While every two stroke bike (even same model and year bone stock) can be ever so slightly different with jetting requirements, there are some general bands. I think the N3EW needle will be too lean, but will come back that.

This is just my opinion and experience, others will vary. I have an 02 YZ250 with just about every possible mod/tuning trick to make it the best single track bike possible for me. I'm a slow senior C type guy that rides a few harescrambles a year and spends the rest of the time riding black diamond single track. My goal was smooth tractable power for climbing loose, rocky, rooted, rutted single track. Majority of my riding on any particular day will happen between 1500-4000 ft.

I run the OEM pipe with FMF Turbine Core II sparky. Ignition retarded, 11 oz flywheel weight, head cut to lower compression slightly (like the YZ250X), squish corrected run pump gas reliably, and 18" rear wheel. In addition to this, I run a G2 throttle tamer. It you are light and looking for smooth easy to use tractable power, I would stick with the stock reeds.

The combination of the engine mods along with the way the bike is set up, it chugs and hooks up almost like a fourstroke in nasty conditions. Really softening up the compression (relative to MX type settings) on both ends along with the heavier 18" tire with more sidewall makes a big difference. The throttle tamer really helps in the those low throttle opening aka slow conditions when navigating over over rocks and roots to keep traction (along with an active clutch hand.)

Now, back to jetting. I currently run a N3CJ needle in its second clip, 48 pilot, and 172 main and 32:1 fuel mixture. I own a full array of pilots, mains, and needles (N3EJ, N3CJ, N3EK, N3CK), so have tried a lot of combos. E or C on the needle denotes when the taper starts and J, K, W the width of the needle. W being the widest and leanest.

As Byke already mentioned, dont jet or change your oil mixture for spooge. Jet for feel and the engine performace you are looking for. An MX bike being tuned for max hit and hp will run towards the leanest hottest burn. For me running tight single track, I am looking for control and trying to smooth any hit to keep track as well as keep the engine cool. So I go more towards the rich spectrum.

When I went too lean on either my main or needle, I would get heat related run on and or knock after long knarly climbs. My motor simply would get too hot with a W needle on really long climbs. I know the new bikes come stock with that needle and it works well for many, just not for me.

Speaking or rich vs lean, a slightly richer carb setting will also smooth the hit. Its all relative and a fine line, but I think you get the picture. For me MX hit big power is a detriment. My bike runs clean, has never fouled a plug in years, has good response, more than enough power to loft the wheel at will.... but smooth. Not that it matters, but my bike gets about an inch long dribble of spooge after 2 days of riding on single track. None in the open like Moab or SoCal. You honestly cant get rid of it with a turbine sparky unless you are on a track or riding somewhere wide open alot.. unless you jet it dangerously lean. I wipe off the very small collection oil dots on my fender before loading it up.

Anyways, long book of a response. I think if you are trying to set the bike up for single track/traction you can play with your current needle first to see if you really need to go leaner (drop it two clips and ride it).

Let see what Eric (2SYS) says.
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Sours: https://www.bayarearidersforum.com/forums/showthread.php?t=522546

Yz 250 woods bike

I have owned my 01 since I bought it new & have tried several different configurations before arriving at what seems to work best. I run an FMF SST pipe & their "Q" series turbine core spark arrestor... Please don't be an idiot, & DO use a spark arrestor! No one likes forest fires...or being turned away from a riding area &/or being fined for not having a spark arrestor or because their bike is too loud. I have also used the Pro Circuit Works pipe & spark arrestor, but like the FMF combo I have now better. I also run a Boyesen Rad Valve & it rocks... I have tried the V-Force reed valve & didn't notice much difference between it and the stocker (besides the fact that you have to buy 2 sets of reeds).

Don't mess with your gearing unless you split the cases & install a wide ratio gearset. 13/50 is only useful as an alternative to a wide ratio tranny on the tightest nastiest trails that can be found, & it turns your bike into something that has to be shifted every 2 seconds with a pitifully low top speed. 14/52 would be better in a pinch... It basically splits the difference between 13/50 & 14/50. I run 14/50 & because my bike is perfectly tuned & I am a skilled rider, it works just fine.

Stock jetting should be pretty close for our area this time of the year when temps. are between 60-80 degrees, but you may need to go leaner when it gets between 80-100 degrees, or in the middle of the summer when the humidity is high, especially if you ride up in the mountains. One persons perfect jetting is rarely another's... You should learn how to fully understand / implement changes in jetting yourself & experiment a lot.

Be careful not to take the easy way out & drop the main jet way down until it runs crisply. Experiment with different needles & clip positions until you get good results in the 1/4-3/4 throttle range while still using a larger main jet so you don't wind up with a lean situation at full throttle. White spark plugs & metallic silver looking stuff mixed in with the black spooge which drips from the power valve vent hose are bad, mmm-k...

Just for reference, the leanest meanest jetting I have ever run with my particular configuration is: Air screw-1 turn out, Pilot Jet-48, Jet needle-N2EJ (2nd clip position), Power Jet-55, & Main jet-175. However, yesterday when I rode up in the mountains in Blairsville, I ran this configuration: Air Screw-1.5 turns out, Pilot Jet-50, Jet Needle-N3CW (3rd clip position), Power Jet-55, & Main Jet-175. I have never needed to change the power jet or slide valve.

The drag strip at Durhamtown Plantation (quite possibly the coolest place on earth) is great for testing your carb. configuration...you can have a buddy watch & listen which helps when selecting a main jet, then once you get that right, the rest is easy! The same jetting (if done properly) should work in any application, woods or otherwise. You just have to change it a lot to get maximum power...without damaging your motor, depending on the weather conditions. Or, you can just err on the (only slightly) rich side, & it will run fine. As long as you don't foul spark plugs or find black exhaust spooge all over the bike & your back, you should be lean enough & you won't have to rebuild your top-end constantly.

I got a bigger see-through tank a couple of years ago, & would highly recommend it to anyone. It beats walking 5 miles back to base camp amidst wild animals which could eat you if they felt like it without a gun!

Hope that helps.


Sours: https://dirtrider.net/forums3/threads/yz-250-woods-bike.133217/
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“I’ve been running Apex heads with the SX dome on my two yz250s for the past season and I must say I am pretty impressed.

The head gives me a noticeable power increase in bottom end into the mid-range. I race woods and occasionally moto and this head changed my engine into a luggable, torquey, four stroke like machine. When riding back to back with stock motors the difference is night and day. I can literally pull a gear higher in many sections/turns. I have not noticed any drop in power on the top end.

I did not need to make any jetting changes with these heads and have had zero issues with detonation even on 100% pump gas. The customer service you get from Matt is very personable and responsive to any questions I have had. The bang for the buck you get with these heads goes much further than any other motor mod I have used.”

“The Apex billet head with the MX dome was a direct bolt on, required no jetting changes or other tuning. I noticed an improvement right off the start, it came onto the pipe sooner and faster and felt like it never fell off. The head gave me a much wider power range to work with and easy to manage for a 20min moto. This head is deceivingly fast and easy to work with. The bike was a 2019 YZ250, Apex MX head, Boyesen Rad valve and a FMF Fatty with a Powercore2 silencer.

I’ve also now got about 30 hours on my 2017 YZ250 that has had the head machined by Apex Technical Innovations to the XC dome specs. The motor produces lots of low end torque and revs through the power range very smoothly, yet still having the ability to be lugged right down low. I’ve also noticed an impressive gain in fuel usage. 2017 YZ250, Apex XC head mod, Boyesen Pro Series reeds, Stock pipe with FMF powercore2 silencer and a GYTR offroad flywheel.

“I’ve had some time now to put about 15 hours on this Apex Technical Innovations head on my beta (21 300 Race edition). I have to say this thing is awesome. Since 99% of my riding lately has been technical hard enduro I went with the XC dome to squeeze more grunt and low end lugability out of it.
The biggest difference I noticed is improved power delivery. Especially on the bottom end to into the mid I could feel a pretty noticeable torque increase. So much so to a point where I’ll be changing my gearing to be taller since I can now pull taller gears. This has helped me in a lot of tricky spots where traction is key. The power curve feels VERY linear now compared to stock. If you are wanting some more lugging power and mid range the xc dome is the way to go!
Apex also has an MX dome that gives a power increase more evenly across the entire powerband and an SX dome which turns the motor into a fire breathing monster. I’ve ran the SX head on my last two YZ’s, but the type of riding I’ve been doing has changed lately from mx/xc to hard enduro.
A couple other things I noticed, the bike starts extremely quickly. Even more so than stock. The last 3 races I did I got the holeshot. The bike runs a bit cooler as well. The head visibly has much larger water jackets than the stock head. This is where the motor goes boom so the larger cooling capacity makes sense. Doing a lot of rock gardens and technical hill climbing my fan kicks on less often with the head.
I have no issues continuing to run 93 pump gas with any of my Apex heads. The only jetting change I did was going in a 1/4 turn on the air screw. I needed to make this change previously anyways.
If you’ve never tried a head before i would compare the power difference to double the performance increase you would get out of full exhaust system + reeds. If I had to choose between buying an aftermarket carb or a head I would much prefer the head. Plus id have a bunch of cash leftover that I could spend on important stuff like spoke coats and replacement horns. A pipe will move the power around and give you an increase in some areas but this is more noticeable. This is the best bang for your buck motor mod you can do to a two stroke

“I finally got a regular ride day tune and test the new head, back to stock jetting and its dialed wow the bike felt perfect I was loving the day, me and a buddy on his beta 250 where equal. Feel like its exactly what I was hoping for I could hold 3 gear almost everywhere, I was really enjoying the ride, thanks again so much. Keep up the good work!”

“Hey, I got to spend to time on the beta yesterday evening. I gotta say Matt you have done your homework here just like the yz.
The Mxc dome has more torque down low, will lug forever. Places I was having to use the clutch a lot on 2nd gear before is no issue at all now. Mid-top is a major improvement also, soon as it comes on the pipe it just keeps pulling, before the power was flat on top. Definitely a major improvement over stock from bottom to top.”

“This Apex Cylinder head felt almost like a displacement increase. More torque down low, more mid range and definitely a screamer on the top. My 14 year old rides it all day long on the weekends with no jetting changes, on 10% 93 ethanol pump gas. It seems to run very cool and consistent for an 07 with thousands of hours. Highly recommended for an easy, bolt on, very noticeable upgrade.”

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“I had my stock head recut to his xc specs and I absolutely love it. By far the best change I have made to my bike. The jetting was very easy to get dialed in and the bike runs much better. Throttle response and power are both greatly improved. More power everywhere, but also easier to control that power to find traction. I ride lots of single track 2nd and 3rd gear, plus lots of technical hill climbs. Apex has their sh*t together. You will not be dissapointed.

“I had them cut my stock head to the XC spec and it works great in the woods! Well worth the $70.”

“These guys have some of the top of the line billet products for the YZ250 2 stroke with awesome prices to match. Thanks heaps.”

“First ride with the sx dome tonight and was impressed with the change in how the power was put to the ground. Lots more low end and a seamless midrange. I was able to stay with some guys on 450s that usually I’m just not on pace with. That’s from the added low and the fact that I could concentrate on the track and not putting the power down. I’m a vet pro and this is a great option for what I do considering I jump in the woods and do some arena x practice. My complete setup is pro circuit pipe and silencer, v force reeds, vp, and now the apex head.

“Matt at Apex is great to work with. I got my billet head with the XC dome installed on my YZ250X tonight. As some of you may know, the OEM head doesn’t clear the frame when trying to remove it on some bikes. The billet head from apex is machined so that it is easily installed and removed with no clearance issues. I’m a huge fan. The bike has much more usable power down low and a nice pull all the way through. Nice work!”

“I Went with the xc head for tough single track riding. I have noticed after the xc head install that the power is so much more smoother and controllable, = better traction. I can ride harder, faster, and longer than before also due to not getting as tired with the smooth power. I highly recommend Apex for your yz needs. Great costumer service and top of the line products at a very good price.

“I can’t say enough great things about how well this SX/XC head works on my YZ125. makes more low and power as promised. easy bolt on and go. small jetting adjustment. highly recommended for vet riders having fun getting back into the sport and faster riders wanting a more tailored power delivery”

“First of all their customer service is top notch! But on top of that, I got the xc head on my yz250 and it makes a huge difference. Moves the power around where you want it and makes it much more controllable than the typical on/off power the yz250s are known for. 10 out of 10 would highly recommend!”

Sours: https://atinno.com/testimonials
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For yz250 woods jetting

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