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03 rm 250 stumbles at low rpms


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I just got this 03 and here is the jetting that was in it...

165 main 45 pilot stock needle in the 3rd position and a 6.5 slide

This is what I have tried to resolve the stumble or raspyness just off closed throttle to about 1/8th throttle.

165 main tried a 48pilot(too rich) and a 42 pilot with the n3wk needle from the 01 and a 6.5 and tried the 7.0 but felt that combo was leean in the mid.

I also tried recomended 165, stock needle in number 2, 7.0slide.

every setting i played with the air screw for best results but this thing still has an awkward raspy like stumble to it just off idle( right where one would be poking through a large rock pile, or cruising through the pits) am I missing something? It seems to be best with the 165main, n3wk needle in number 2 from top,42 pilot and air screw 1.5 turns out.

Might I need a 40 pilot?

SoCal, right now when testing and riding is 80-90degrees, 3000ft in elevation

Any other suggestions. a 42 and 40 pilot are way leaner than the stock 48 which concerns me, and am I better running the leaner slide with stock needle or the stock slide with leaner needle. I also noticed in the fiche that the 03-06 use the same cylinder part number, so can i run some jetting from an 06 that works nicely? I had the same issues years ago when I had my 02, then I got a KTM 300 and changed the needle to the one recomended from the shop I went to and that thing ran very clean. Is this stumble just a trait of those early years? I am fustrated:banghead:

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I have an 01 and I have 46 162 and I have the same little hesitant at very low throttle. When I am just crusing at low speed it is ..b ba b ba ba ba.

I have been playing with the air and idle adjustments I also have spooge out the back on a nice long run. short runs no spooge. I can turn my air screw out about an 1/8 to a 1/4 turn and the spooge disappers but then it seems to be too lean it sits as 1 3/4 turns out now. it has a hunt or serge of and idle I have awesome throttle every where else. 1/8 on all the way up it is smooth and beast. I don't know if I should drop it or raise it on the pilot to get rid of this condition or live with it. what you think.

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I got a 40 pilot jet today I am gonna try. I have been talking to Bill's pipes about the jetting on this thing and he was leary about how lean my pilot is until I told him the bike has a Boyessen Rad Valve on it. He recomends not to use it as they found with testing for Suzuki they got better power results from the stock reeds on the 125's. I dont have the stock reeds or cage for this and it is almost 200 bucks, for that I will put on a Vforce. I also am gonna remove the FMF turbine core muffler and install a standard moto muffler to see if that helps. Pretty much I am shotgunnin this with the adition of parts one at a time. luckily I can rob some stuff from my KTM 300. Choke knob( could be leaking and you would only notice at small throttle openings. I am also gonna check float level however it doesnt leak out the vents much when I twist the bike to put on the stand. Also gonna mix 50/50 race gas and regular 91 to see if that helps. They said any of these could be my problem, or possibly none of them. Oh well, I am still gonna ride tommorow, I will just have to go faster.LOL.

Anyone else experience this and fix it or did most just live with it?

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Well, havent found the problem yet. I tried all jetting combos, float level is good, and I even trimmed back the plug wire and reinstalled the cap and a fresh plug. no matter what I do, it wont go away or even seem to get better or worse. I have found that the 40 pilot jet seems to be correct since the idle peaks at 1.5 turns out so a 40 it is, untill it gets cold again. So here is what I am running now:

168 main

40 slowjet or pilot

n3wk needle in #3

6.5 slide

1.5 turns out on air screw

50% race gas

Maxima K2 at 40-1

I think my next step is to replace the rad valve with stock reeds, anybody got some for an 03? Maybe Vforce? I wonder if a head mod might be helpful? It helps KTM's run cleaner down low. Or maybe a carb wing? That helped my KTM too. Any other ideas or info???????????

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I see a few possibilities.

Plug may be weak and higher octane gas will eccentuate that.

Running lean on 1/8 throttle may cause stumble and you may need to go richer or just turn up the idle to get around it more simply. Run it richer and turn up the idle.

Put in a pilot and stick with it whether you have to turn it all the way in or all the way out and that will tell you which way to go. It's gotta get better at some point or it's the gas.

At that throttle, 1/8, the pipe and exhaust and reeds really aren't going to have much affect. And I'm guessing you take a screwdriver with you and change airscrew as your riding terrain changes and different conditions? If I'm running slow in the woods it's one thing, but if it it's climbing slate piles it's another and temp and humidity even on the same day can change in those environments. I question the 1.5 turns is best cause 'that's where rpm peaks'? Huh? If it runs like crap, who cares and I find that a meaningless tuning tool for me. When i get the 'bang, blah, bang, on idle down, off idle/steady idle when riding I make it RICHER with the air screw which isn't 'best' for acceleration but is better for smother riding'.

You also say 'stumbling' but is that a 'bog' stumble or a 'lean hang/miss' stumble? You also state nothing is solving the problem so you need to look somewhere else. How many kicks to start when hot, and how many when cold?

When you turn in that air screw on the 40 pilot will the engine kill? Also, from what I understand, the pilot is ALWAYS on and by going DOWN to 40 on the pilot from 45 (minus 5) and UP to 168 from 165 you've effectively leaned out the top, by two,. 45-40 is 5. 168-165 is 3 giving a decrease of 2 total fuel delivered though that only matters from WOT.

Another way to check rich or lean on the bottom is to run it on choke and see if that's better or worse.

Sounds like you haven't done a plug check, either?

Edited by chemicalanarchy
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OK. I have good fuel, 50% race and 91 octane. Same gas I am running in my 300 which I road yesterday without a problem. Premix is Maxima K2 at 40:1.

The bike runs raspy and loads up only under a load on bottom but pulls clean throught the mid. I am gonna take the carb apart under the dirrections of my dad(desert racer from the 60's) and soak it(minus the needlestack orings and plastic parts) in laquer thinner for a few hours and blow it out with compressed air and retry some street runs. He is thinking the air correction jet(inlet side of the carb, not really a jet but a passage) is blocked up and causing this. Worth a shot. If that doesnt work, I am gonna air test the motor and maybe find a leaking primary crank seal( my 380 leaked but didnt run bad, just smoked alot, this bike smokes some but not enough to detour insects,LOL). If it were rich in jetting or a pluged up air passage in the carb I would think it could smoke a bit too from being effectively too rich.Lots of drool on the silencer which was in perfect condition and no longer plugged up after I burned out the carbon and repacked it( FMF TurbinecoreII). I also tried a moto silencer and no help either. So far I have eliminated the pipe and silencer, air filter is fresh and oiled( not overly done). Possibilties might be:

1 Clean carb extremely well

2 Bad crank seal on primary- gonna drain trans fluid and measure amount then perform air test.

3 Weak reeds- after air test gonna remove and inspect(Boyesen Rad Valve)

4 Inspect top end and power valve assembly

5 If all mechanicals are in good condition, gonna have to check electrical

🙂:banghead::banana::banghead:🤣:banghead:🤣

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A pilot jet and where it turns you tells you what? It told this guy nothing who has now had three different sizes in it. I've had 3 different sizes in my 250 and one or the other really doesn't matter much for the fuel I run and temps from 50F to 90F. With every jet size you can almost always turn it in far enough to shut it down though you might not be able to get it lean enough. Pilot jet ain't that bigga deal and we can see it didn't solve his problem.......

Yea, he can monkey with the needle, but if he has it all the way leaned out and that tiny pilot jet and it still loads, that ain't gonna be the problem, either.

Well again, you are going through all that and not checking the spark plug? A crappy spark plug can 'miss' when it's going bad at low rpms and then fire normally at higher rpms.

Laquer thinner won't work or at least won't work as well as soaking the carb in acetone.

Since you have the carb off, why wait to check the reeds which are 4 bolts and five minutes away?

I had nearly this exact same problem with an rm80 and wasted all too much time moving the needle up and down and this and that and finally the problem was fixed by changing the fuel mix because the high octane 'race gas' I make wouldn't ignite on the bottom end unless we changed the stator to all the way advanced and then the top end sucked.

Changing fuel is the simplest and fastest test and with all the leaning and other changes he's made he has CLASSIC symptoms of too much octane and/or not enough advance.

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I guess we are gonna agree to disagree on the pilot as in many cases it's useless and changing it on my bike is a PITA though we can look at triumph406 from the spooging rmx thread who tried numerous pilots and got nothing? I don't know, was he at 1.5 turns with each?

Originally Posted by triumph406

I have the jetting tutorial, and have started with the pilot jet. I've tried 50/48/45/42 pj's with pretty much the same result, except the smoke is reduced with the smaller sizes. Turning the airscrew doesn't change the idle speed with any of the pj's, even after thouroughly cleaning the carb. But it still starts 1st kick when warm, and even in gear. Confusing.

I guess you could say that told him where the problem wasn't, but that's a huge waste of time as far as I'm concerned and he really solved nothing and later in the thread the 'experts' go to oil recommendations?

My point is to spend a ton of time to fix what is a 'small' problem by ripping the bike apart.............though he still didn't check the reeds............when a CHEMICAL solution of switching premix ratio and/or octane fuel could give you an instant fix with the problem.

As I said, I tried everything with one bike and EVERY OTHER 2s I have runs fine on 30% alcohol and 87 octane, but the one bike. Got sick of it and switched that bike over to straight 87 octane which BURNS FASTER and that solved the bottom end problem after spending 2 weeks, at least, of dicking with one thing or another...............actually, that's a year on that bike as it ran like that last year and I didn't like it so I let it sit until the kid was old enough to do some himself. I've never calculated the octane on that mix, but with all ratios being equal, I didn't think it could make that mucha difference, either, but it did. Actually had the same with a 25cc weedeater which ran like hell on 42:1 and 87 octane, but ran perfect when switched to 50:1 e.

Now the needle could have a HUGE affect as you said, but that depends on jet size and needle type, too, or it may be minimal for the trouble, too. On my 4s the needle made a difference, but when monkeying with the needles on the 2s, they all went back to the original including the bike with the fuel change which went through five different needle changes (or more with jet changes) to try and get it going off the bottom.

In the end, either way may work, but five minutes of mixing gas vs ripping my bike apart........I'll mix!

Edited by chemicalanarchy
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...

This is what I have tried to resolve the stumble or raspyness just off closed throttle to about 1/8th throttle.

165 main tried a 48pilot(too rich) and a 42 pilot with the n3wk needle from the 01 and a 6.5 and tried the 7.0 but felt that combo was leean in the mid.

I also tried recomended 165, stock needle in number 2, 7.0slide.

Hi there

I would rather try one change at the time, every little change effects the behavior of the engine. Midrange is the needle position. Have a look through this site carbtuning

regards

Arnego2

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I'd still like to know how it runs on the choke. If it really gags he knows the bottom is rich and/or slow to burn and might try moving the needle down. If it then runs fine while the idle may be high, he knows it can go richer on the pilot.

He also hasn't said if he runs it so rich on the air screw and a low idle screw that kills quick on throttle off that you have to keep revving it to run, if it comes off the bottom any better. Do the same with lean as possible on air and turn idle screw down as low as possible and see how long it takes to drop down.

These are simple tests where you don't have to change anything and even if you have to run a higher idle to be above the hang, it ain't the end of the world.

I'd change the plug, too, just for the hell of it which is only 5 minutes.............

And I'm not saying anything about his riding or that I'm a great rider, but I sure can't think of too many times when I'm cruising around on only 1/8 throttle even when overgearing behind the kids..............oh, and do you have a FWW on there?

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Plug was changed, then another new one after that. Made no difference. I am also gonna remove the plug cap and chek it for an open or overamount of resistance, I figure at low rpm's it could be breaking down or have an open in it but at higher rpms the spark could jump the open or extra resistance. It wont run with the choke on. Starts on 1st or 2nd kick every time, hot or cold. I have it set to idle and the rpms drop to idle speed right away when throttle gets closed. It runs the same way whether it is on plain 91 octane or a mix of 91 and 110 octane race gas at 50% which I would guess yeilds approx 99 octane or so. As far as I know, the motor is stock and the compression when I checked it when I got the bike was 155psi. Seemed a bit low to me for a slightly used top end( at least that is what the seller told me, 4-5 hours), however my KTM 300 has a milled head and is at 190 psi. What should a stocker be?? I have to be honest, I have a bit of motivational loss right now but am gonna go clean carb tonight and possibly give another update tomorrow. Thanks for the sugestions so far.

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Are we chasing a little bog right off idle to 1/8? I have read all the post, but it looks like I went off day dreaming or something. To me, the carb has been picked to death and I would move on to search something else at this point. Has the stator been moved from stock setting? You also may have a weak conection or dirty quick conectors? Mite look for a wire that maybe holding togather by just a few strands. Mite just be a bad kill switch, unplug it and see what happens. If I was at this point, those are things I would look at for peace of mind. I would realy look for that pinched wire around the triple tree. Maybe just a bad ground from the wire harrness to the frame. I'm just tossing some ideals out that I would look at.

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bambam, i have an 06 with exact same problem (if you can call it that), and have tried fiddling with jets and related, but suspect its a design thing, given several (not all!) have the same. to me its only a mild annoyance when tooling thru the pits and sitting on the start line. going leaner did help, but not get rid of it. at least its all there where its needed (eighth onward).

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Thanks for all the inputs. Yes bog or raspy or poor throttle responce(only under a load) from off idle to 1/8 throttle. I looked at the plug and it is dark brown bordering towards black. cleaned the carb extremely well soaking it in laquer thinner and blowing it out with compressed air. I checked the operation of the power jet solenoid(working) and tested the throttle position sensor(working good too) according to the tests in the book. I think I am done with the carb for now. Removed the rad valve and the reeds look very good, great tension and no frays or splits. This is the first time I have ever seen a tripple reed, Fiberglass beaker shape, then a carbon center, finally a fiberglass large reed, all stacked, really strange. My stock radvalve on my KTM only has a 2 stage. There was quite a bit of oil on the tip of the reeds and cage but I cant tell what kind it is. I air pressure tested the motor the best I could(plugged intake boot and exhaust, used punches to plug vent hoses, and I have a special plug for the spark plug hole and it also is the place to fill the engine with 7 lbs of compressed air<has a guage>). It dumps presure instantly to 3 lbs and holds there for more than a minute before bleeding down anymore. No obvious air leaks so I would guess that the crank primary seal could be leaking( maybe where the oil came from on the reeds, more than I have ever seen on a reed cage during a disassembly). Checked power valve opperation and looked for carbon build-up through exhaust port, it seems to move freely and little to no carbon build up. Also checked resistance on plug wire which checked out good too. My next step is to capture my trans oil during draining and check volume, since I put 750 cc in, I should get close to that out. If I come up short, that seal must be leaking. After draining oil, I am gonna disassemble motor out of frame, take off primary cover and replace the seal along with ignition seal. Also gonna replace top end so I have a known starting point and I will know for fact that mechanically the engine is sound. If this doesnt work, I guess I can start testing stuff be taking parts off the wifes 01RM 250(cdi,coil,ect....).Any other ideas I might have missed.🤣🙂🤣:banana: More fustration.

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Dude, as others have said, 'It's a design problem' which is how it looks to me!

You've done everything right and gone above and beyond and it's obviously jetted correctly. The problem is 'under load' which I also had with the one bike cause 'my load' was different than a kid weighing 100lbs less and the bike acted differently off the bottom. We adjust the air screw out on the trail as needs be.

Your compression is so ride the damn thing and don't be ripping it all apart as I don't think it's gonna fix it. About your only option is to advance the stator as somebody else said and see if that then gives you a top end you can live with OR you can idle over the problem and just have a high idle. Since jetting hasn't changed a thing, you could still try moving the needle, but I doubt that's gonna change it, either, especially since you said it drops right off on throttle off.

You didn't say if it has a FWW.

As for checking the seal leak with the tranny change, a simpler way is to change from oil to ATF-F, or vice versa and see if there is a change in color or smell of the exhaust and then there is no measuring.

Try your stator and I know this is a heresy for some of the 'experts', but many around here run wildly different spark plug gaps. Closing or opening your gap by 0.010 could make a huge difference though it may also change performance at another area, ie, I've finally opted for 0.040 on my 250 as 0.050 wasn't as good on top end AND if you want to see how it does change, a turbo auto had an NGK factory gapped to 0.028. The new denso TT plugs are gapped for that car at 0.035. OMG! Different from factory and different from another plug! Anyhow, it's only 4 plugs so I tried from 0.025 to 0.045 and the wide gap was good before the turbo kicked in, but then sucked so I went back to 0.035. Yea, that's long, but the point is that something small might make a big difference and a plug takes only 5 minutes to change.

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Thank you guys for any and all input.I think I got the problem solved now, if not completely it is alot better and probably wont interfere with riding now. Heres what is the new news. Today I was gonna pull the motor out and dissasemble and inspect. I drained the oil from the trans and mesured it. I cam out with more than 750 cc so I figure there is no way the primary crank seal is leaking( air tested a few days ago too). Then I moved to inspecting the power valve spring tension. I think(not sure because my dad was talking to me while I was loosening the bolts and it couldve moved) there was no tension on the spring, shouldve been at least a 1/2 turn to be in the oem possition. I also replaced the stock tripple stage Boyesen radvalve reeds with 2 stage ones left over from my 06 KTM 300(stock on that bike). The tripple stage didnt make any sense to me as far as flow is concerned due to a huge area for fuel mixture to get trapped at the reed block from the petal design. I then installed an all together different jetting than I was running( actually started with what MXA recomended in 03) and tweaked from there. I ended up with a 45 pilot, air screw about 1.3/4 turns out( peaked from feel not idle this time) 7.0 slide, stock needle in #1 position,and a 165 main. It still is a tiny bit raspy on the bottom but has a very smooth transition into the midrange power with no loading up or running issues. I ran the bike with a fresh plug up and down my street multiple times at less than a 1/8th throttle opening and checked the plug, light chocolate brown:banana:. Then I ran it more at 1/4 to 1/2 throttle untill I got the reading I was looking for, chocolate brown again:banana:. I will have to wait for my main test(will do it on a local dry lake to me). I am pretty sure I am very close now and cant wait to hit some trails in the hills near me.🙂

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