new bike jetting

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#1
I have a new YZ 250 R. The stock jetting according to the manual is #50 pilot and #175 main with N3EJ needle. I am at about 900 feet here at Lake Lanier. The bike runs great, but seems too rich on the low end. Also, I am not an aggressive rider, and will be learning for awhile, since I have not ridden since the 70s.

My question is should I put the #48 pilot jet in and lower the needle clip from the middle posistion? Or just jet down and leave the needle alone.

I am very expierienced in two stroke jetting on stand up skis (full race motor) but have not tuned bikes before. The plugs are black, and I have fouled a few, but I understand that is normal if you don't ride hard.

Also, can you only get the 10w-30 type SE at bike shops, or is that regular auto oil. The manual says SAE 10w-30 SE. I have two tanks run through it now and would like to change the gearbox oil per the book.

Sorry for the long post, Thanks, John
 

biglou

#2
You can easily drop the pilot to a 48, 45 or even a 42 if you want. I'm no jetting master by any means, but if I remember correctly, I've been told by Rich that you won't seize the motor by jetting the pilot too lean. You should notice snappier throttle and hopefully less fouling. Also, note that plug reading is done after a max load, WFO run then chopping the throttle, shutting down immediately, pulling and reading the plug. I've never done it myself, but I have read about it on here (and I did stay at a Holiday Inn Express last night...). ;)
 

bclapham

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#3
48 or a 45 pilot on a yz250 sounds about right, thats what i run. try the pilot first then try the needle
 
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#4
I have an 04 YZ and what fixed the fouling for me was an extra 1/4 turn out on the pilot air screw adjustment and switched to Amsoil 100 percent synthetic race 2 stroke oil @ 40 to 1 ratio, was using Yamalube @ 32 to 1 and there was constant fouling and alot of spooge dripping out of the silencer. The bike run's awesome now.
 
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#5
a bike should not foul plugs, even if it isn't ridden hard. As for the oil type, I wouldn't use an automotive grade oil as a motorcycle has a wet clutch, where the tranny oil also lubricates the clutch plates. Auto motor oil has alot of anti friction additives , wich WILL cause your plates to slip.(they will than have to be changed as normally, cleaning them will not fix the problem.) Normally, manafacturers recommend 10w40, motorcycle gear box specific oil(such as belray gear saver), or atf.
 
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#6
Thanks guys. I am using Klotz R-50 full synthetic race oil, but with only a few tanks through it, I have probably not rid the system of the Yamalube "break in" tank full the dealer put in, and it was mixed 20:1. Witha few more tanks run through, all of the Yamalube should be history.

I did install the 48 pilot and opened the air bleed 1/4 turn. It ran much better down my street, for about 500 yards, till the plug fouled...but I was expecting it and was already headed back to the garage hehehahah. It is odd runs fine for my short 2 or 3 hour sessions, and then fouls the next time you start it....like after washing it back at the house. Hopefully this problem will be gone with the great advise on this board.

I love how the manual mentions nothing about how the whole rear end tilts up to get at the carb, or just to remove the large drain plug to rejet.....but I am sharp....I caught on pretty quick..LOL

Thanks again, John
 
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#7
John,

The 48 should be about right, make sure needle is on clip 2 and not 3.

I have been fighting the fouling problem on my 03 yz250 and just pulled the carb today and found the float out of adjustment. Made the adjustment and did a quick test ride in the yard. So far so good.

There have been a few of us with this problem.

I hope this fixes the fouling.


Guy
 
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#8
I have not checked the float yet. The dealer even warned me about "keeping it up in the band" or fouling would result. I ofcourse felt the same way as another guy posted here....that a properly tuned motor should not foul plugs just because it is not ridden hard. He told me this after the deal was done, so I just took it as a challenge to resolve the issue.

I am assuming you want me to raise the c clip one notch to let the needle sit down in the jet more, hence leaning the mixture?

I will also be running NGK BR8EIX plugs (irridium), since I stock them for my Jetski business. These cost a bit more than the others, so all the more reason to solve this.

If this continues with proper jetting and synthetic oil, should a heat range change be in order? I am always worried about deto!!

Other than this issue the bike is fantastic, very well designed and manufactured machine. I hope I get many years of service from it.

I will report back after I run a few more tank through it.
 
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#9
sjmaster,

I think the stock setting on the needle is clip 2 (from the top).

Try doing a plug reading before it fouls.

Mine always looked great.

Then after sitting for a little while it would load up after you took off.

Guy
 
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#10
Still fouling plugs, the saga continues

OK, the motor runs a bit snappier with the next smaller pilot (47 I think)> Ran one whole tank today...motor still ran flawlessly, like it did with the 50 pilot, just a bit snappier. Never really had a crap coming out of the pipe (as others have described), but there is less gunk dripping out of the PV vent line.
SO....I took the carb off (love those two phillips in the top cover, they are now stainless allen head ) and I found the float at 3.9mm The book says 5.5 to 7.5 And "THE FLOAT ARM SHOULD BE RESTING ON, BUT NOT DEPRESSING THE NEEDLE VALVE" well, this has me stumped....it has a tiny stainless spring loaded pin on the end that the tab applies pressure to to close it. The float definately pushes that pin down to the end of it's travel...maybe 1.5 mm or so. Is this what they mean by resting on but not depressing? The spring for that tiny pin can not hold the wieght of the floats....for sure...it pushes it down with ease. So do I set the hieght with this pin in the needle depressed? I don't see any other way right now. Please advise.

Also, the clip was in #2 (from the top) should I try moving it to the top for the leanest setting?

I am guessing the tiny pin and spring is there to ensure shutoff under bouncing conditions.....watercraft Mikunis and Kehiens do not have these little pns in the needles.

ALSO what hieght gives a leaner (less fuel in the bowl) setting....I would say the higher (7.5mm) is this right???

Thanks in advance, John
 
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#11
sorry forgot this info..could not edit

I also wanted to say that it did not foul the plug till after I got home and started it again to run around the street and terrorize the dogs. I am guessing that the cool down cycle must cause the oils to penetrate and foul the plugs. Is there anyway to save them? I tried cleaning and heating with a small torch flame, but the ohm meter still showed about 10meg ohms if I remember correctly.

Thanks, John
 
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#12
OK it get stranger The stock jet is supposed to be a 178, and it is. Since the bike came with #178, and # 172, I assumed it had a 175 in it, since the dealer said it comes with one higher and one lower. Well, heres the wierd part. The original jet in the carb is a 178 S (with the logo mark), and the extra jets that were supplied are 178 and 172 WITH NO S mark !! Whats the S mark?? I measured the holes on both "178" jets and they are exactly the same!!
ALSO...I se how the float pin works for measuring hieght....you just can't hold the carb upside down as the instructions state. If I roll the carb over till the float tab hits the pin, it is right on 7.5mm ! So, all that said, I guess I will try moving the clip to #1 posistion, since I have the 48 pilot in there. My riding is getting better, I am staying in 1/2 throttle or more quite a bit now. If this persists, should I try a smaller pilot or 172 main?
 
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#13
I've never heard of a YZ250 R. What year is it? I'm in the same boat as you kinda. I have a '01 YZ250.

My bike runs perfect all day until it sits in my garage for a week and then I go start it cold. It seems like this happens to alot of YZ250 owners on this forum. It fouls 60 seconds after idling. Sometimes I can get past the fouling part and then it will run perfect all day.
I live at the same elevation as you pretty much -1025 ft. w/ 70's weather
main: 178 S(whatever the S means) just bought a 175
pilot: 48
needle: N3EJ and 2nd clip position
air screw: 1.5 turns out (Ive never messed w/ it bet next time I am)

My bike doesn't or has never bogged before and I think it has great throttle response but I'm not sure b/c I've only been riding for 5 months. My plug is always oily or a dry, black ash color.
 

merlinnn

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#14
I have an 03yz250 and have not experienced any of the problems you guys are unfortunately having. I am currently running a 50 pilot, the first leaner needle from stock,(not sure of the part no) on the second clip and stock main (178). plug is standard running 40:1 motul 800 or shell advance oil. I am still learning so the bike is not always in the powerband and am yet to foul a plug.

The temperature I have been riding in varies between 10 to 32 degree's ( sorry not sure how to convert) elevation would vary between sea level and 2000 feet.

I respect your patience in regards to plug fouling as i would have spat the dummy long ago.
 
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#15
Not really addressing your question here but it seems you should have a method for jetting before you begin, not just putting this or that jet in to see if it gets better. The fouling thing is beyond me, but if your plug is black it is probably too rich. That said, make sure the float bowl setting is correct, that you have enough air coming through a clean air filter, and that you have the manufacturers recommended jetting specs handy. Then go through your whole jetting procedure from start to finish on a warm engine. Do you have a procedure?