Noob with a YZ250F

Hi everyone, I'm new here and a total noob rider.

I recently decided I was going to finally get myself a motorcycle and hit the trails around here. I had never ridden a motorcycle before, but I had ridden lots of 4 wheelers around our ranch. I managed to snag myself a '04 YZ250F in pretty good condition for a only $1550 (seems to be a great deal for what others around here have been selling for!). A little maintenance (oil change, clean carb-it had been sitting a while, new chain and sprockets) and it starts right up!

I have a couple questions about how it runs though. First, if I get it going good and fast, then let off the throttle and slow down, it backfires (crackles?) a lot! I had figured this was normal, but I was reading somewhere on here and I came under the impression that it needed some mixture adjustment or something. Is this normal behavior?

Second is I noticed one of the first times I took it out I was running it kind of slow going up a little bumpy offroad incline in 2nd (I didn't want to give it too much power accidentally in 1st). I noticed what seemed to be the chain kind of making a knocking noise and the movement kind of chugging. Sort of like letting off the clutch in a car wrong and it kind of chuggs off... The bike seemed to have plenty of power available and it didn't sound like it was going to stall so I figured maybe I had the chain too loose or something. Is THIS normal? Now that I have a better feel for the bike, I don't really run it like that anymore but I'm just curious.

Third question is, is there any must-have accessories or things I should get? The bike is pretty much all stock ATM. I don't think I need much more power right now, she seems to have plenty in that department for me! I'm looking at a ProMoto Billet kickstand, a JD fuel mixture screw, and I need some sort of spark arrestor. I'm debating whether I should get the ProMoto billet endcap and possibly silencer, or get a FMF Q4.

Hopefully it will quit raining for a while so I can ride some more without tearing up the ranch TOO much! I'm going crazy waiting... I'm totally hooked. I can't wait to hit the trails!

Thanks for any help!

First off, being the bike is new to you, I would have the valve clearance checked while your doing maintenance. You can do this yourself. It takes like 30 min at most.

The backfiring is your jetting. If the bike is jetted for summer and your riding it now, the jetting is a hair off due to the weather.

The chain slack should be about three figure width, measured at the screw for the top chain guide toward the front of the swingarm. It sounds like you could've done shifted there, It's pretty hard to stall these bikes, yet they will kinda bog if you to high in the gears.

If your looking for more power, I would'nt touch the exhaust. You won't gain anything for the money you'll spend. If you just want it to be quiter, then I'd get the Q4 or powercore. I have the powercore and it has 2 differant inserts i can put in it to quit it down. The smallest insert makes it basically the same pipe as the Q4. I'm not sure how the Q4 is setup and don't know if it has removable inserts or not.

And i'm with you on the rain crap. Hope this helped you out.

Must have item in my opinion would be a whole JD jetting kit and adjustable fuel mixture screw. It might help a little with the backfire. Some crackle is normal when you let off the gas but if it sounds like gun going off behind you then it needs to be looked at or you'll blow your muffler

Thanks for the info.

I'll see if I can find some specs on the valves. The guy who sold it to me said he just had them checked by a shop, but it couldn't hurt to check again.

Is the chain tension checked when it is sitting on its own weight, or when the sprokets and swingarm are in a straight line?

I was looking at that jetting kit, but since I'm not really looking for more power just yet I wasn't sure if it was worth the money. I do live up at about 2200 feet so maybe the kit is in order... I couldn't find any clip reccomendations for altitude so I left it stock.

As for the exaust, all I NEED is a spark arrester so I'm still torn between the cheaper endcap or the better(?) Q4...

The JD kit will provide power and they provide different main jets and needles for different altitudes. You can put all the horsepower add ons you want, they ain't gonna do squat unless the jetting is spot on

The chain is checked with the bike on the ground. Take a look at the jetting sticky, you may find a good setup for your altitude that you can start at, then fine tune from there.

I bought an 04 from a friend a year ago also, definitely check the valve clearances again, simple, easy to do and it'll give you peace of mind. As far as what you felt while riding, I agree with educkett29 "It sounds like you could've done shifted there, It's pretty hard to stall these bikes, yet they will kinda bog if you to high in the gears." But if you did just change sprockets and chain, it would be worth it to check the tension, theres a link to a downloadable pdf of the owners manual floating around, definitely worth checking it out for all this maintenance stuff.

As far as the spark arrestor, I was in the same situation you are, de PMB S/A were around $120 and a new exhaust was worth at least $250... I bought an Lexx exhaust with S/A from rocky mountain and am extremely happy with it. It's worth checking it out, according to me it is quieter during normal riding, during WOT it sounds like the stock one, simple to install, well made. And my butt dyno says it does free up the engine a little. Link:

Check ebay, they sell them cheaper ($175)

Oh check the alignment of your sprockets, do not go off the marks on your axle blocks because they are usually off

Thanks for the help everyone!

When I changed the chain and sprockets, I had the bike on a bucket and I adjusted it to about 2" slack, I think that's what I read in the manual. Then a friend came over and said it was way too tight, he took it off the bucket and had me adjust it until it was about the same slack when he was sitting on it.

How do I check the alignment without the notches? Will it work to just measure the distance from the adjuster to the wall of the pocket, or do I need to check if it is square off of something else?

Thanks for the help everyone!

You're Welcome. I cannot speak for everyone, but as long as you're brave enough to ask the questions, I'm willing to help you the best I can. I don't know everything, but I won't BS you either.

How do I check the alignment without the notches? Will it work to just measure the distance from the adjuster to the wall of the pocket, or do I need to check if it is square off of something else?

You can check your rear wheel alignment by measuring the center of the axle to the center of the swing arm pivot bolt as seen below. Adjust each side so that they match in distance and make sure you have the necessary slack in the chain. Be sure to be very precise with these measurements, down to the millimeter.


OK, will do. Thanks.

I'm going to hit the TT store and spend that additional 10% I got from signing up. Talk about icing on the cake!

EDIT: looks like the shop is down... Hmmm guess I'll have to wait.

OK, I've got my cart loaded... I'll probably put in the order tomorrow, but I have two things left to decide:

First is to get a FMF Q4 or a PMB endcap. I could go with the FMF Powercore, but I heard that it isn't quiet enough even with the insert. Would I need the silent insert for the PMB endcap to make it quiet enough for trails?

The second is the kickstand. I like the design of the PMB better, but it looks like they are weaker than the TrailTech. The TrailTech look worse, and stick out more, but they say they are strong enough to stand on while starting and they are cheaper. I'd like to be able to start it on the kickstand, but it isn't too hard to start without the kickstand... Should I just screw it and go with the PMB? They should have them on the Thumper Talk store!


I have a quitcore insert for my fmf powercore and trust me, it's quit. fmf told me it was the same insert the q4 uses, therefore it turns the powercore into a Q4.

IMO ProMotoBillet kickstand is hands down the best. It's very solid and good looking to boot. It's well worth the extra $$$. Another thing to consider would be a set of Cyrca hand guards. They are virtually indestructible and will save your levers and your hands. I prefer the CRM(center reach mount) version.

You can save some money on the jetting by just ordering a needle from an '09 yz250f and doing the A/P mod.>>>

I would also highly recommend an adjustable fuel screw for fine tuning on a daily basis. It'll greatly help in keeping the jetting right as the temperature and humidity changes, which effects how easily it will start if stalled hot.

I have a quitcore insert for my fmf powercore and trust me, it's quit. fmf told me it was the same insert the q4 uses, therefore it turns the powercore into a Q4.

I'll take your word for it. It was an older thread I was reading so things must have changed. Is there any advantage to the powercore? I guess it's probably more powerful than the Q4 when the insert is removed. Sorry for all the noon questions:bonk:

Thanks for the link to the carb thread. I think I'll get the jet kit anyway just so I have all the stuff, but knowing never hurts!

Looks like Ill be getting the PMB kickstand and just start it on the ground... thank goodnes for long legs!

MY THOUGHTS: Being that I also live in Idaho (riding 2-4 times every week) and have a 09 and '10 yz250f, I can honestly say that you will not have one bit of trouble with the FMF powercore4 with the quiet insert, which sells for less than $30.00 (insert). Just this year, I've passed 4 separate 96 db sound checks before races and have come in well below the mark. I've put the powercore4 on my last three bikes and plan to continue doing so in the future.

As far as the PMB exhaust tip goes, all of my friends have put on the PMB turn down insert with it and have passed sound check, but I'm not sure if it would pass without the insert - being that I do not know of anyone who has been tested without it. It is worth considering that by time you buy the end cap and the insert, the cost difference between the PMB set up and the FMF exhaust is rather negligible to me.

Finally, don't even waste your time considering any other kickstand! Always go with the PMB kickstand. It is tucks away safe and out of site and before every ride I fire the bike up, put it in gear, and lean the entire bike up on the kickstand to oil my chain. I've had one on my last two bikes and I've never seen any weakness in the kickstand from doing this or had any bad experiences with it. Plus, it has an extra large base to stand the bike up and it has never given out and dumped the bike on even the most soft sidehill yet. I can't say the same about any other kickstand, most likely because most kickstands lean the bike way far over and have a foot print/base the circumference of a quarter.

Cool, thanks! Looks like I'll be getting the PMB kickstand and the Powercore exhaust.

I checked the valves, It felt like a .004" feeler would just hang on the intake and a .007" would just hand in the exhaust. Those are both just slightly over the metric spec form minimum gap. The guy did say that he had it done by a shop after the initial break-in and it hadn't been run much since them. I had to get a feeler set from NAPA and grind it narrower to get it to fit, but it is still done in round inch increments, not mm. Does anyone know of a place I can get metric feelers that are narrow enough to get to the valves without modification?

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