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DR-Z 250 Jetting Saga-Part I, II & III

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Greetings:

For your amusement, here's a chronicle of my (pathetic) efforts to unclog and rejet my new 2003 DR-Z 250.

From the showroom floor, it was jetted pretty lean. The third day I had it the temperature dropped 20 degrees, and the bike would not idle for anything. I made some mods – namely, I took the snorkel out of the airbox, increased the size of the main jet one step (from a 127.5 to a 130) and increased pilot jet one size as well, … at least I THOUGHT I went up one size. It turns out I went up TWO sizes. More on that screw-up later.

After being rejetted, the bike ran and idled much better, and had a bit more power in the middle and on top. But it exhibited a weak, flatulent bottom end and abrupt power delivery at about 1/8 to 1/4 throttle. Also it was back-firing (i.e., belching out through the carb, mostly upon a chopped throttle). Frustratingly, the position of the pilot screw does not allow the rider to adjust the screw while the bike is idling, so I rode the bike a couple of days in this condition.

In the meantime, I ordered a Uni filter and a 2R Racing billet exhaust tip for the bike. I didn’t want to spend a lot of time chasing jetting around. However, I was interested in diagnosing the off-idle bog that I was getting, so I could understand what changing the airbox and exhaust might do. I asked some questions on the TT jetting forum and also researched as many jetting tutorials as I could find. Unfortunately the symptoms my bike was exhibiting can be described as a “classic lean pilot condition” or a “rich pilot circuit.” Both too rich and too lean will cause a bike to sputter and bog, and my lack of expertise prevented me from diagnosing it properly.

For the sake of experimentation, I pulled the carb and raised the needle one clip position -- at least I THOUGHT I raised it one clip position. It turns out I LOWERED it one clip position, which is my second blunder for this saga. And to add insult to injury, in the process of removing the carb I mutilated the "intake net" -- a little collar made of screen that hides inside the engine side of the carb.

I ordered a new "intake net," and boldly put the bike back together without the old deformed one. (The parts guy at my Suzuki dealership assured me it would be fine this way; he seemed to think the purpose of the intake net was to catch debris, but this doesn't make sense. My thinking is it prevents cavitation in vapor flow.)

Anyway, with the needle in this leaner position, the bike ran about the same as before, only the abrupt behavior was probably slightly smoother.

This weekend I installed the Uni and the 2R Racing billet tip. (Incidentally, 2R Racing sells billet exhaust tips via eBay. The tip advertised for the DR-Z 400 also works on the 250. It turns out the 400 and 250 use the same exhaust canister and exhaust tip!) I also drilled six 1” holes in the airbox and plugged them with Uni filtered plugs.

After I buttoned everything back together, the bike started up _amazingly_ well. I was going to just turn the motor over a few times with the kicker before hitting the e-start, but the bike fired to life on the first kick, which was a pretty weak excuse for a kick. However, after it warmed up, it bogged and died as soon as I tried to give it throttle. It restarted, and eventually I milked it into motion. It sputtered and choked on the bottom, but then cleared out in the middle – basically the same behavior as before, only maybe a little worse. I took the carb off again, and discovering my error I set the needle to the position that I'd intended to set it -- one position higher than stock, i.e., fatter. The result was that it seemed to smooth out the low-end abruptness a little bit, but it didn't seem to have much effect.

Thinking the bike was jetted too lean -- since a fatter needle position seemed to help it -- I unbuckled the carburetor, rotated it sideways, and adjusted the pilot screw out ½ turn – to 2-1/4 turns out. It seemed to run a little smoother, but was still flat off the bottom. I went out ½ turn more, and it didn’t seem to make much difference. This led me to think the pilot was probably too lean, so I pulled off the carburetor and LO and BEHOLD, the pilot that I had originally installed was TWO steps up from stock, not just one. Was this thing running too rich the whole time?

So I installed the size-40 pilot that I thought I installed the first time, and I re-set the pilot screw to about 1-1/2 turn out – approx the stock setting. I turned on the fuel and hit the magic button. It turned over, but would not start. I struggled with it for a while, then I turned the idle down several turns. The bike then started, but would not take any throttle. It just spluttered and died no matter how carefully I tried to give it gas. Also it did not want to stay running, but turning the idle up made it impossible to re-start.

This is where I’m at right now. This morning I’m going to try to find a few minutes to turn the pilot screw out ½ turn, and see what it does. I’ll post the results when I have them. In the meantime, here are a couple of pics from my recent modification efforts.

Have a good week. MORE TO COME.

Regards,

MTB

Airbox-plugs1.JPG

Exhaust-After.JPG

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DR-Z 250 JETTING SAGA CONTINUED

=========

Greetings:

After playing with the carburetor today, I've gotten my new 2003 DR-Z 250 to run pretty darn well. Specifically, I made the following adjustments:

1) Turned pilot screw out to 2 turns. After I did this, the bike started and idled fairly well, but it backfired into the carb and popped a lot on deceleration (chopped throttle). The power delivery off idle was quite abrupt.

2) Turned pilot screw out to 2.5 turns. After I did this, the bike ran much better, but still burbled quite a bit on deceleration. Power delivery still pretty abrupt.

3) Turned pilot screw out to 2.75 turns. Now we're talking! Once the bike heated up, the burble essentially disappeared. It pulls strong across the powerband, although it seems a little "crackly" in the midrange. The low-end power delivery is still a bit abrupt, but seems quite a bit better. It doesn't lurch and puke nearly as much as it did before.

4) Raised needle clip one position/lowered needle to stock position (one position leaner). This cleared up the crackly behavior I was getting in the midrange. It seems to pull nice and steady from about 1/8 turn up to WFO.

I'm still planning to pull out the pilot jet and go back up to the next-richer jet, with a lean pilot-screw setting. As the weather gets colder, I think I'll want someplace to go with that pilot screw, and the 40 pilot jet won't give me the headroom I need to richen the mixture much more.

With these mods, the bike is running as well as I've had it run, I believe. However, it's considerably stronger, particularly on the bottom and in the midrange. When I first got this bike, pulling a wheelie was an exercise in brute force. Now it's almost effortless to pull a wheelie in 1st gear. In 2nd it takes a tug on the bars, and in 3rd it's still a challenge. But at least now I won't ram into those logs on the trail!

Best Regards,

MTB

P.S.: Here's a picture of me adjusting the pilot screw. What I do is unhook the throttle cable fittings from the retaining hooks, but I leave the cable end-fobs in place (see far left, where cable end is still attached). Then I loosen the two clamps holding the carb in place, and rotate the carb counter-clockwise so the bottom comes up on the right side of the bike. I've gotten this procedure down to a science. I can do it without detaching the fuel line or the cable fobs, but it's impossible to do it while the bike is idling. Suzuki's got some 'splaining to do about that one!

Pilot-screw.JPG

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JETTING SAGA CONTINUED from Part II:

====================================

Greetings Again:

This evening I pulled the carb and put the fatter pilot jet back into my DR-Z 250. I cranked in the pilot screw and then backed it out to 1 turn. A few minutes later I started it up, ... but only after coaxing it along mightily. (It was still warm from the previous test, but not hot.) After riding it about 10 minutes or so to bring it back up to temp, I determined that I had what seemed to be a lean condition. It was a bit boggy, popped a lot on deceleration, and didn't want to idle right.

Back to the shop. Another 1/2-turn crank out on the pilot screw, and the popping now is muted to a burbling. But the bike still wants to choke and lurch at throttle positions of 1/8 throttle and less. Another 1/4-turn out makes it worse -- or at least substantially the same.

In other words, I'm basically right back to where I was when this saga began -- suffering a case of flatulence, at 1.75 turns out on a 42.5 pilot.

However, now there's one important difference: I know where to go from here (I think). I've already tried the 42.5 pilot with settings at 2 turns out and greater, and it just got more spluttery. Thus I need to return to the 40 pilot jet, put it at the 2.75-turn setting that it seemed to like, and ride the heck out of the thing.

Am I throwing in the towel? Sort of, temporarily. With the 40 pilot, and 2.75 turns out on the pilot screw, it was running pretty well. I'll experiment with 3 turns out and more, but I think I need to stick with the 40 pilot. Otherwise I'll be chasing the jetting forever, and the only riding I'll do will be to test the latest jetting mod. No thanks.

Thus endeth the saga, for now.

Best Regards,

MTB

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G'day, you may be able to get some help from www.kientech.com about your fuel screw extension, I got one for my drz400 and it made tuning it a breeze, Jesse doesnt list one on his website but he is very helpful. while on the subject of the drz250, do you think this is a underated bike that has potential to actually go fast on? I have an xr250 99' also and I have no trouble at all at suprising people at how fast she can move along the trails, do you think the drz would be an upgrade to the XR or is it a sheep in sheeps clothing? sorry to get a bit side tracked there.

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I like DRZ, Plenty fast to me, Handles well, Compares well to XR250's I've ridden. I like the Electric Starter. It takes my 185# body any place I want to go. I only wish the after market companies would product stuff just for the DRZ

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G'day Floppa:

I haven't owned my DR-Z for very long, but one thing I can say for sure is that it has plenty of go-fast potential. It is not a racebike, but the suspension is very good and I go faster on it than any bike I've ever owned. That's not saying very much coming from me, because I'm not a racer. However, my buddy CK _is_ a racer, and after riding my DR-Z he had to think about it awhile before deciding whether he could go faster on the DR-Z 250 or his WR450F. He decided that his 450's power would make up time in the straights that the DR-Z would gain everywhere else.

So I suppose it depends on what type of riding you do. If you're riding big, open, fast trails, then a bigger, faster bike is better. But for tight woods stuff, I love the DR-Z. It's the perfect combination of high-performance and friendly manners (except for the annoying off-idle bog that I'm trying to get rid of!)

Comparing it to the XR250, ... I'd have to say it's a new-generation of dirt bike, but not so new-gen that it requires a rebuild every 30 seconds. To me, the DR-Z is a better value, off the showroom floor, than an XR250 is. It has electric start and better suspension. It also has some nice features that make it simple to convert to a dual-sport -- i.e., the lights are wired to go on with the ignition key, etc.

I love my DR-Z. Now if I could just get the jetting sorted and ride the thing, ...

Regards,

MTB

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g'day Mtburr, thanks for your thoughts on the drz, Ive ridden,raced,bashed and crashed many bikes and I think these older tech (aircooled) 250s are underrated,I love the woods so I must test ride a drz. back on the topic of your off idle bog, all the jetting curcuits over lap a little so dont make more than one change at a time, so the initial needle function can richen/lean the idle circuit slightly, I know on my 400 it is very sensitive to adjustments on the slow/idle circuit. also I think your carby has an accelerator pump on it, and if this isnt squirting correctly (maybe to much) it will cause a off idle bog. this is a problem on a lot of modern four strokes. do a search in the drz400 forum about accelerator pumps or something similar, there is a lot of info there that is related.

regards floppa

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Alright, here's my story. I'm 15, and I live in Santa Clarita, CA. The middle of the desert. I just bought a DRZ250, 01 model, and at first was only mildly impressed with it. But after I got home from school, I would take parts of the bike apart to see what may be bogging the bike down. I did all the airbox, carb, exhaust, and screen fixing, and now this bike hauls ass. I couldn't believe what a difference it made! The thing pulls like a tank! I ride with my dad, who is the best rider I have ever seen. (Ex- MX and Enduro Champ) He rides an 04 DRZ 400. I did the same mods to his bike for him, but the 250 smokes the 400 in almost anything but fire roads. Granted, in straights, he catches my ass real fast, but the engine mapping is so well done it's amazing! you can literally put one foot down and do donuts with this bike, without dropping it. Try that with a race bike. This may seem insignificant, but when you're on the trails, you need this level of control more than you realize. also, I love how well the compression slows the bike down. on high speed downshifts, you better hold on! Anyway, I know I'm typing way too much, but I just wanted to share how happy I am about this bike. I'll get pictures soon.

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What are your final settings? main jet, pilot jet, pilot screw and clip position? Also, what is your current temperature and elevation? Finally, what are the mods to the airbox and exhaust. A nice summary would help others have a point to compare with.

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here are mine:

Main-137.5

Pilot-stock setting

Air-Fuel- 2.5 turns out

clip-middle position

i cut about five, 1 1/2 holes in the top of the airbox, removed the backfire screen, and bought a Yoshimura RS-3 Full system. I live at about 1000 foot elevation, and in summer it's about 110 average, winter about 60. I also added a 51 tooth Renthal rear sprocket.

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here are mine:

Main-137.5

Pilot- 45

Air-Fuel- 2 turns out

clip-middle default

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