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General jetting questions regarding my 98' cr250

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Well fellas let me start off by saying this forum looks amazing. I've been over at Allthingsmoto for a while and just discovered this forum today! This is in fact my first post however I'm not new to cr250's. I actually owned this 1998 cr250 in question, about 3 or 4 years ago and I sold it once I moved off to college...Well to make a long story short my buddy found the bike and I was able to buy it back 3-4 weeks ago. So, most of the 4 years it's just been sitting. It went through 2 owners that never rode it. When I got it it still had the same airfilter, plug, everything that I had on it when I sold it :busted: Good news is it has just been sitting though. First thing I did was new air filter, radiator fluid, and gear oil changed...

This bike still has amazing compression and I still have the same spark plug from 4 years ago in it. I know, I know....It WILL be changed this weekend. It's been running pretty good but now that it's fall here in Memphis, TN the bike has started to run a little lean. I experienced some surging a couple of weeks back. A mechanic friend of mine suggested I get a bigger pilot jet, and for the mean time he enriched it by screwing in the air screw until it was just 1/8th of a turn from fully closed.

Let me start by giving you some stats on the bike:

1998 cr250

32:1 ratio - Klotz synthetic race oil

Pro Circuit Platinum Pipe

Stock silencer (I think)

Stock jetting (175/55/42)

Now, this bike is somewhat new to me all over again. I know that in the winter the bikes tend to go lean and that means it's time to go richer on jetting by buying bigger jets. I would not be nearly as concerned if the bike was rich compared to lean, for the obvious reason of having it seize up.

Let me also add that I was able to download the 97-99 service manual for my bike and for the weather and altitude we have right now in Memphis, the stock jets (what I currently have) are exactly what the manual calls for, along with the air screw 2 turns out from closed.

I've been buying everything I can think of to get this CR fully dialed in. So far I've ordered a complete carb rebuild kit that includes EVERYTHING from jets, gaskets, o rings, seals, float, needle, everything...These are the stock jets and I also ordered a second set of stock sized jets...Getting ready to do the carb rebuild kit soon but here's where I get confused...

Part of me says keep the stock jetting in it since it is exactly what the manual calls for with my weather and altitude right now, and then part of me says well the bike was surging the other day and we had to turn the air screw way in (rich) to get the surging to go away so maybe I should go bigger on the pilot and main??? Tell me what you think.

Today I got to messing with it, and I was basically trying to set the air screw at the stock setting (2 turns out) along with setting my idle (which on 98 was by the top of choke knob) I had it set @ 2 turns out, started the bike and the revs would sort of hang up there so I thought to myself..Too lean...So I finally got the air screw to 1 turn out from fully closed and it ran like a dream...BTW 1 turn out is the MINIMUM amount I'm allowed before going richer...So I'm right on the fence right now.

Now the part that worries me is that the power is completely there and it runs great, but I also know that can be a symptom of it being lean...That crisp clean power can sometimes be deceiving...

Bottom line..I want to get this thing dialed to where it's just outside of being rich, and not set myself up for a motor seizure!!! After all, I'm not racing...I'm running 32:1...and I just want it right...The temps and altitude are very moderate changes here in Memphis so I shouldn't have to go far from the stock 175/55/42 jet sizes. I was thinking just the pilot and main, but I'm still very new to jetting so please feel free to correct me or give me any of your input!

Very glad to be here fellas! :busted:

Griffin

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Wow, anyone? I'm thinking the only way to be certain if it might be lean is a plug chop...but all I know is has the jets that the service manual calls for and runs great. I'm brand new to jetting though so I'm trying to learn so some replies would be great.

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im dealing with getting my cr125 jetted right for cooler weather. i found a chart that has correction factors for jetting, and my jetting was VERY close to the corrected size.

i will be bumping main/pilots by 1 size. keeping the needle the same. current size are 165mj, 55pj. corrected for 0-1500ft at 50 deg. is 166.6 mj, 55.5 pj. i know these are bseline figures, we'll change the jets then ride test it and see.

just google CARB 101 that will take you to the page.

Edited by argclh6670

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on my 97' cr250 PC pipe at 1000'-4000' elevation I run 172/55 jets and around 2 turns out on the air screw, I will usually play with the air screw once I get the bike warmed up and only turn it a little just to get a nice crisp rev off idle...I have had the same jetting and done the same air screw tuning since I got the bike in 2000. never had a problem and never fouled a plug...

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Move the clip down on the needle one notch. This will raise the needle making it ritcher and will probably take care of most or your problems. The needle clip effectes the 1/8 to 1/2 throttle region mostly. The air screw does idle to 1/8 and they do overlap each other and jetting is way morel complicated than i am making it seem. So if you make the needle richer you may then need to make the air screw leaner (turn it out)

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Move the clip down on the needle one notch. This will raise the needle making it ritcher and will probably take care of most or your problems. The needle clip effectes the 1/8 to 1/2 throttle region mostly. The air screw does idle to 1/8 and they do overlap each other and jetting is way morel complicated than i am making it seem. So if you make the needle richer you may then need to make the air screw leaner (turn it out)

Thanks for the info but my service manual says to always Re-Jet the main before changing clip positions in order to not do any damage to the top end...Not really sure how that protects the top end but I do remember seeing it!! Tell me what you think! I still need to lean out on the air screw 1 full turn so this method with dropping the clip may be able to do that for me!! Just don't want to do any motor damage obviously! Thanks again bro.

Griffin

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Hey guys well the jetting is feeling good. Still need to do a plug chop even though we haven't been riding as much (burrrrr) but anyway I have noticed a lot of people recommend disconnecting my electric power jet solenoid on this bike, and doing something else to make up for it? I think maybe it was changing the needle but if anyone is familiar with what should be done to negate that power jet solenoid that'd be awesome!

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Hey guys well the jetting is feeling good. Still need to do a plug chop even though we haven't been riding as much (burrrrr) but anyway I have noticed a lot of people recommend disconnecting my electric power jet solenoid on this bike, and doing something else to make up for it? I think maybe it was changing the needle but if anyone is familiar with what should be done to negate that power jet solenoid that'd be awesome!

I wish i could remember what jetting I had in my 97. And I dont understand all these negative reviews of the PJ solenoid. I never had a problem with mine in the 4 years I owned it. Ill go back and look threw my service manual and see if I made a note of it. If I remember right it was the same jetting Pro Circuit recommended since I was running a works pipe.

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I wish i could remember what jetting I had in my 97. And I dont understand all these negative reviews of the PJ solenoid. I never had a problem with mine in the 4 years I owned it. Ill go back and look threw my service manual and see if I made a note of it. If I remember right it was the same jetting Pro Circuit recommended since I was running a works pipe.

Pro circuits jetting spec is 165 main, 55 pilot (stock) 42 power (stock) 1.5 turns out on the air screw and a smaller needle (numerically) @ 2nd clip position

I am running the stock jetting 178 main, 55 pilot, 42 power, but I am less that 1 turn out on the air screw so need to bump up that pilot to 58 I think and I'm also running the stock needle on 3rd clip position

So the only difference between stock and pro circuit is the main jet, the needle, it's clip position and the air screw turns. The power and pilot jet stay stock.

Stock jetting actually calls for the 175 main but now that it has dipped below 60 deg it calls for the 178 which I threw in there but honestly I'd love to run the pro circuit but that main seems wayyy too lean to risk it, unless the different needle makes up for it @ the 2nd clip position.

Is raising/lowering the needle rich or lean? I forget I'd think they would make up for that lean main somehow not to burn up the top end.

I also have had 0 problems out of the power jet solenoid but I think it gets a bad wrap because they decided to make it an electronic part when most are mechanical, so that is setting it up for a far better chance of failure than a mechanical one.

I guess I won't mess with it as they say if it ain't broke don't fix it BUT I'd like to know what I need to do IF it does fail!

I am new to jetting and my bike feels okay but I have no idea to tell if each section of the jetting is rich or lean ie pilot, needle, or main....I always thought a bog was a rich condition but apparently it's lean. I get very confused on the symptoms and sounds or rich vs. lean. Definitely need to do a plug chop asap.

Let me know what you think Keith! Thanks!

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Raising the needle is richer and lowering is leaner. Needles with a lower number are richer and higher numbers are leaner. The first 2 numbers on the needle indicate the taper angle. The last 2 numbers on the needle indicate the diameter of the needle. Page 1-25 of your service manual gives a pretty good illustration of the needle and what the numbers mean. The taper of the needle determines how fast the fuel can flow past it as the throttle is opened and the needle raises.

You can have both lean and rich bogs. A rich bog is kind of like a gurgully feeling(engine takes a moment to clear up then takes off) where a lean bog the engine will actually die because it is starved for fuel(an extreme lean bog). The best way to test for your bog is to increase the jet size. If the problem gets worse you have a rich condition. If it gets better you have a lean condition. This prevents you from going too lean and causing engine damage.

Im not positive but I think that pro circuits jetting recommendations are for sea level at 70 degrees.

Your air screw is set pretty rich. You could go up a size on your pilot and open the air screw to see how it will run. Or you could just open the air screw and see if the engine stalls when you open the throttle quick while actually riding.

Remember to keep accurate notes of your starting point so you can go back where you started if you need to. And keep track of what works well for your usual riding area and different temps(summer vs. winter)

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Oh trust me I remember every little adjustment that is made but why do you suggest leaning out the air screw and then hitting it to see if it will run? It would run @ 2 turns out (stock) this past weekend at the track, but only on decelerating I had a little bit of a lean surge...Could of been nothing though but I'm pretty sure it was a slight lean surge. Man, I hate learning how to jet my bike in the winter when it goes lean!!! If it was summer and richened way up I wouldn't hardly care about doing all the ride testing cuz it wouldn't hurt the motor. Bike is running great and all but the air screw is out of spec and I just want to figure out if I'm still too lean...Because I've learned that powerful feel can be deceiving and actually just a lean condition!

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