RM 250 Jetting Question

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1/31/2018 6:39 AM

I have an 03 Rm 250 and it runs really good, but I am having a problem going off some jumps. It is primarily jumps that have a decent run up to them and I'm in 3rd gear I have it pinned but then I let off a bit to 1/4-1/2 throttle (truthfully I'm not exactly sure) and as I hold it there it seems to bog a bit. Then it has a hard time hitting the throttle as I try to blip it at the top of the take off. When it happens what pops in my head is a the motor trying to cough up a bubble. I am leaning on either my pilot jet or my clip being a tad rich. My biggest question is if I was to try leaning out the needle one more clip would that be enough to run too lean to hurt the motor or potentially just enough to make it run bad? I'm having trouble noticing if I'm going to 1/4 throttle or a little more because that is two different adjustments. Diagnosing at idle between lean and rich is not too hard but when riding especially when it really only happens when going off a jump it is a little harder. Does anybody else recognize this problem?

On bigger jumps I don't really see this problem like at thunder valley the big triple in the back I am pretty much pinned in 3rd the whole way to the top and I don't have this issue.

main 162( I think)
Needle stock
clip position 2nd ( from bottom 1 leaner than stock)
pilot 48


1/31/2018 7:35 AM

Hi, what elevation are you at there in CO? With my 03 RM250 I ran a 48 pilot, NECJ needle on the 3rd setting and a 172 main jet. Check your float height and definitely check the reed pedals for chips on the ends or any frays in them.


1/31/2018 7:44 AM
Edited Date/Time: 1/31/2018 7:44 AM

Duh haha the most important thing I forgot elevation! I'm at about 5300' at the track. Pretty different than sea level.
I actually may be a 46 pilot its been a little bit since I have been in the carb.

Ive actually replaced the reeds and ive checked out the float height but its a little hard to understand how to get it exactly right. I may have to check that out one more time.

I know I do get a lot of black residue on my rear fender and on the inside of my number plate but it does not run out of the exhaust unless I ride trails which is at 9000 + and I don't rejet for that but it runs good enough up there and I don't really care if its not quite perfect I'm not racing.

I do have a full bills pipes exhaust too


1/31/2018 1:44 PM

My buddy bought a 03 RM250 and when I was doing research on them, I do recall reading that the 2003 model is notoriously hard to jet. Good info found here though: https://thumpertalk.com/forums/topic/810883-03-rm-250-jetting-advice/


Positively, absolutely 110% obsessed with anything MOTO.

1/31/2018 2:48 PM
Edited Date/Time: 1/31/2018 3:24 PM

Thanks for that link. I will have to look through it.

One main question I have is Can you go one or two sizes and 1 clip leaner on the needle without worrying about harm to the bike. I am not afraid to try stuff I have lots of jets but It worries me to try stuff and hurt the bike.

Digger29 is the NECJ needle worth getting over the stock needle?


2/1/2018 8:46 AM

The necj needle with a 04 or 05 slide is the ticket for the 03. Stock slide makes the bike run rich in spots.


2/1/2018 2:30 PM

Polishhammer wrote:

The necj needle with a 04 or 05 slide is the ticket for the 03. Stock slide makes the bike run rich in spots.

What he said^^^ Also the 03 has a pretty abrupt power delivery and will respond well with a 12-16 oz flywheel weight. Smooth's everything out and actually makes the bike faster too. Stock pipe with a Bills or PC silencer or the complete Bills combo is the best combo for it. My 03 was Andrew Shorts 03 SX bike. He got hurt around the 3rd round and I was able to purchase it as is with the Showa suspension and Vortex 10 way programmable ignition. It came with a few flywheel weights and I settled on the 16 because it really worked well with the porting for me and the tracks here in New England. The cylinder was decked .030 and the head was cut to work with the cylinder. The bike barked. I'll find a pic of it and post it. I remember the day like it was yesterday getting the call from the trucking company and taking the cardboard off of the crate and just going "OH MY" The thing was insane and just as he raced it at I think the Dallas round.


2/5/2018 6:24 AM
Edited Date/Time: 2/5/2018 8:39 AM

That must be a cool bike. Would like to see that.

How do I locate the different slide? It is showing I cant buy it where I usually get my oem parts.

Found the needle though, would I just put the clip in the same position that I have now and start from there.

Did a little more reading on the slide changes. At my altitude an 8 slide was maybe recommended. Also may need to run my clip in the 1st position. This part worries me because I do not want to screw something up? IM guessing I will notice it running bad if its too lean and I can change it?

Just found out JD jetting sells the slides. Kinda pricy at 70 bucks but way cheaper than oem. When I called them to see if I should go with a 7 or an 8 they really did not give me much info but instead pushed their jetting kit. I know there needles are good but Ive already got the mains and pilots they come with and oem needles are 11 bucks so if I could get a needle that was close to the one they recommend (NECJ?) then I would rather do that. I just worry about going too lean and not knowing it and blowing the bike up. I understand jetting on a beginner-ish level but I don't have much experience with actually changing and then testing it. I just don't wanna put a new top end in because I did not know what I was doing.


2/7/2018 7:19 AM

I ordered the NECJ needle so when that comes in I will swap it. I'm scared to go to the first clip in fear of blowing the bike up but I may have to give it a shot. May try second clip first because it is a bit colder this time of the year.


2/7/2018 8:26 AM

''clip position 2nd ( from bottom 1 leaner than stock)''

You haven't got your clip positions mixed up have you?

The top clip is the leanest, as the needle sits lower into the main jet, allowing less fuel to pass through.
The lowest clip position is the richest, lifting the needle up to allow more fuel to flow through.

The top clip, furthest from the needle tip, is generally known as clip #1. Bottom clip is clip #5

Therefor you are currently at #4. So raising the clip to say #3 or #2 will lean out the 1/4-3/4 throttle range.

You will know if you go too lean as the bike will become 'zingy' and eratic
Trial and error is the key to jetting. In some ways it pays to jet the bike wrong, so that you can easily identify rich and lean conditions in the future. This makes temperature and elevation jetting changes easier, as you can tell if the bike has gone rich or lean from the change.
However if you make an adjustment or ride at a different temp/elevation and you think it feels lean, stop riding and go richer.



2/7/2018 8:39 AM

Thanks for that info I typed it out wrong because I did not really think it through. I Knew that though if I actually stopped to think about it. I'm in the 2nd clip position from top at the moment with the stock needle. I think ill swap needles and try the same clip position.

It is easy for me at the track to re jet because I run the stock tank and can just pull the carb to the side and pull the needle out. But on the trails I switch to my desert tank and I have to pull the carb out or the tank off to get to the needle. Kind of a pain in the butt when your buddies are waiting on you to go ride.

I need to go to the track and work on jetting a bit to get a good base line then go to the trails with the stock tank by myself to get a good base line up there.

Thanks for the help guys I will report back once I work on the bike some.


2/7/2018 11:53 AM

Yeah I'd recommend keeping the same clip position to start with. The difference in the needle taper may give you the results you are looking for.
If you make multiple changes all at once, it is easy to get lost as to what has helped and what hasn't. So make your changes one at a time.
I actually own an RM250 too, and also have a large tank for it. I've found the stock tank to be good for at least 1 hour of hard riding. My RM250 is an 08, but for info I run 48, NEDH #3 and a 168 main.

Good luck!



2/7/2018 12:00 PM

Thanks yeah I worry I will run out of gas with the stock tank. I second the multiple changes thing so I will keep that to just one.
I think your numbers are a bit rich for me at my altitude.


2/16/2018 5:01 PM

I put the needle in and it’s spewing gas out of one of the vent hoses. Tomorrow I’m going to pull the carb apart and clean the needle and seat. But I wanted to ask if there is anything else I should check or would that be the only cause


2/17/2018 6:47 AM

lcgordon711 wrote:

I put the needle in and it’s spewing gas out of one of the vent hoses. Tomorrow I’m going to pull the carb apart and clean the ...more

Sometimes you can tap the float bowl with the small rubber mallet or the handle of a hammer and it will usually stop doing that. Try that.


2/17/2018 7:02 AM

Thanks for the tip. I'm guessing doing that is un-sticking the floats? When people say the floats are sticking what do they mean exactly. I understand how the floats work and sticking would mean the they are not floating up to push the needle up to stop the flow of fuel but do the floats get caught on the side of the bowl or does the pin holding them in get sticky or something. I will probably yank the carb out quick and take it apart just to be sure and blow comp air where the needle seats.


2/17/2018 3:01 PM

lcgordon711 wrote:

I have an 03 Rm 250 and it runs really good, but I am having a problem going off some jumps. It is primarily jumps that have a ...more

That particular year, 03', RM250 had a couple of issues that really effected the way the bike ran stock. The first of which was the stock squish. It was huge, around 1.9 mm if I remember correctly. The squish needs to be corrected before you even go into the carb to fix what they have going on in there. The next problem is the 6.0 slide that Suzuki speced for the 03'. It's too rich. You will either need to have the stock slide cut into a 7.0 or buy one. To make up for the overly rich slide Suzuki speced a very lean N3WK needle. I use an NECH needle in my 07' RM. I've tried using an NECJ needle and IMO it's to lean.

If your bike does in fact have the parts/problem that I mention still in there, do yourself a favor and send the head and slide out together and have them corrected. http://www.rb-designs.com/index.html


2/19/2018 6:54 AM
Edited Date/Time: 2/19/2018 8:03 AM

Sorry for the long post,

Thanks for that info Digger,

Just for everybody's info my jetting is set at,
stock needle (N8RH) 2nd clip
42 pilot jet

I have a little update, I fixed the fuel leaking problem I took the carb apart and cleaned the needle and seat and blew comp air through it. Then I attempted to set the float height the best I could. It is really hard to see when the tab is in the right spot, just resting on the plunger thing. Plus I was just measuring an adjustable wrench and setting it to 6.5mm per the manual (well the 2004 manual I have I am yet to find an 03 one). I think calipers would be a much better way to measure this.

Went and rode yesterday, did not have the best day except nobody got hurt which is really good but other than that I showed up and it was already like 20 mph winds. Got geared up and was about to go out on the track and they pulled off the bikes to run 30 min little bikes ughhhh. Then got to go out rode one lap and bike was horrible bogging a lot. So I came in pulled the carb and took the new NECJ needle out and put the stock one back in. Went back out and ran like crap again pretty much the same. So I came back in and figured, I would move the float height some I'm pretty sure that lowered it like 1mm or so a little hard to tell. Then I got back over to the track and they start pulling bikes off for little bikes again. So I wait a while and notice they are getting the tractors ready to prep the track. So I go over and ask the guy since I have been doing jetting work if I could do one lap with the kids and he said yeah. Perfect so I rip one lap and it runs as good as it was before I started messing with it. Finally!

So, I have a couple questions. First I'm 95% sure I lowered the float height, went from 6.5mm-7.5mm or so. I may have went the other way, I was pretty flustered and in a hurry and not really thinking straight enough to really remember everything. Next time ill bring a pen and paper to write things down.

So Since what I did made it run better should I try to drop it just a touch more to see if that helps any more? Does elevation effect float height setting, or is stock setting the best no matter what elevation, or jets you have in the bike at the moment?

If the float is set too high, too much gas in the bowl will that make it run rich, and too low will it make it run lean?

I know I should go back and try the other needle once I figure out the float height problem.

I have been wondering about the JD jetting kit, Its 75 bucks and with their needle and what they recommend if it made it run pretty dang good I feel like it would be worth it. Problem with it is it could just be my float height that is off, and I would not really be learning anything about the jetting process by just putting in what they tell me.

What about the power jet what does that do?

Digger, You are the first person to mention getting the head mod done. I'm not saying you are wrong, I'm sure your right but it seems most ppl, ive read everything I can find from googling the 03's, get theirs to run pretty good without doing that. Also people who are at sea level say to get the 7.0 slide at sea level, based off my elevation, 5300, I am wondering if I should even go with an 8.0 slide?

Thanks for all the help guys, one pro to this issue is I'm learning a lot and currently my bike runs good enough to ride it. Sometimes it gets a little hectic getting a slight bog right before the face of the jump, my strategy is to go real fast so that if I do get a bog my momentum still gets me over and if I don't I just let off at the top and scrub a little bit.

EDIT: just found a 03 manual on ebay for 24 bucks shipped. Pretty excited should have some more jetting info and the fork info should be correct also.


2/19/2018 9:33 AM
Edited Date/Time: 2/20/2018 7:40 AM

For whatever reason Suzuki's machining tolerances in 03' on the rm250 head were off, which left the head having an overly large squish of around 1.90 mm. It should have a squish of between 1.20mm to 1.25mm. I don't even consider cutting the head a modification, as much as I consider it a correction. This is the first thing that needs to be done on that bike in order to really straighten the jetting out. If it's not, there will always be inconsistencies. If your bike is only going to run at elevation, you could have the squish lowered a little more without having to increase the head volume, and still use (93) pump gas.

Check the underside of your slide, right where the needle comes thru, there will be what looks like a star, it's actually the letter K, and next to it is your slide # or cut away #. For your bike you will want to be using a #7, even at your elevation. I have used a #8 in my Suzuki and liked it, but it may not be for everybody.

That N8RH needle is a variation of Yamaha's current N3Ex duel taper series needles. It uses the exact same tapers, but is 1/2 clip position richer. That series needle has a tendency to be rich on the 1st taper and then go lean into the middle, which sometimes causes a stutter at low throttle openings. The Suzuki NExx triple taper needle is just a better design IMO, but that J diameter needle you are trying to use is to lean, Combine that J diameter needle and your cooler temps and there is your reason the bike is bogging, even with your current setup. If you are going to use your current N8RH needle you will need to increase pilot at least 1 size to a 45 and maybe even a 48. Elevation doesn't have as big of an effect on the pilot and needle as it does on the main.

On flat top(held on by 2 screws) PWK's I always set the float up between 7mm--8mm. It's generally a set it and forget it regardless of elevation. If you have it set within that range you will be good. provided the float needle in working correctly.

JD jetting makes some very nice, but expensive needles, and he provides good technical support, but his needles still aren't going to fix your overly rich slide and poor squish.

Once you get the above fixed, you should be right around an NECH needle #3 with a 45 pilot and a 158/160 main jet and a 45 power jet, Start out with the air screw at 1.5 turns out.

If you don't do anything at least increase the pilot on your current setup, or at least turn your air screw in. It should stop the bike from bogging, and don't even try to use that NECJ until the summer.


2/19/2018 10:02 AM
Edited Date/Time: 2/19/2018 10:23 AM

Thanks so much for the info I really appreciate it.

Looks like I will be looking into cutting the head. I am going to look around my area for somebody to do it because looks like rb designs has a pretty good back log. Do you recommend any body else to do it other than them?

I wonder how much it is to get the slide cut. JD jetting has slides for 75 bucks If it is close to that to get cut I may just buy one.

What is a power jet? I think mine stock is 50 and you say use a 45.

I don't have the J needle in I have the stock one in at the moment and really did not get to try the J one out.

Oh and just based of my numbers and what I have in the bike you think I'm getting a lean bog in the beginning with my current set up with the 42?

Oh and why is the 8 slide not for everybody


2/19/2018 12:09 PM
Edited Date/Time: 2/19/2018 12:11 PM

lcgordon711 wrote:

Thanks so much for the info I really appreciate it.

Looks like I will be looking into cutting the head. I am going ...more

Check the squish by using the guide on http://www.rb-designs.com/rb_designs_llc_017.htm to verify your current squish. I can't recommend anyone in your area other than possibly Jeff Slavens of Slavens Racing to correct your head. I have used Eric Gorr in the past for machine work, but now use Ken O'Connor of http://www.kenoconnorracing.com/index.html for all my engine work. The machining of the head shouldn't be more than $75 and to have the slide cut should be about $20. I have been cutting my own slide now for a while now though. It's not that complicated, if you have the right tools.

The Power jet is the solenoid located on the side of the carb. It stays open until a set rpm where it shuts off allowing the bike to have more over rev. It uses jets to control the spray, located under the solenoid. A 45 power jet/leak jet is leaner than a 50.

Based off the jetting that you have listed, I feel that the 42 pilot jet is to lean for that N8Rx series needle. It should be in the 45 to 48 range. I'm sure that 42 pilot is trying to compensate for the rich slide. The pilot jet and slide work within a similar throttle range.

The #8 slide is a little tricky to get to work correctly, it required a lot of testing to get it working the way I like on my 07' RM. I use it with a Yamaha/KTM duel taper needle, but I don't feel confident in giving out the specs for other to use on their bike. I feel as though the #7 slide setups are more flexible. The duel taper needle/ #8 slide setup does provide a slight seat of the pants increase in torque down low though.


2/19/2018 12:31 PM

Thanks again. I already emailed Eric Gorr and will try Ken as well.

I need to find the power jet online somewhere. Not sure how to change it out but I'm sure I can figure it out.

I will swap the slow for a 45 and reset the air screw.

Its tough because I really cant find the issues on the flat ground it just seems to rip but on the track when I land off the small double and hold the throttle a certain position before I hit a bigger double it acts up. Its kinda a hard part of the track to really pay attention.

I don't care if the bike is perfect. I'm not trying to be team Suzuki. I'm just trying to not die out there.


2/19/2018 1:34 PM
Edited Date/Time: 2/19/2018 1:50 PM

Called Ken Oconner and he told me don't do the head unless you want to run race gas.

He said he does not do the slide mod.

Not sure if he does not know the 03 rm and is just lumping it in with all other 2 strokes or what.

I feel like I go on the internet and just get confused. Not anybody's fault just 100 ways to skin a cat I guess.

do you know where to buy the orings on the head so I'm not spending 15 bucks for new oem ones. I'm guessing they are just o rings


2/19/2018 3:03 PM

lcgordon711 wrote:

Called Ken Oconner and he told me don't do the head unless you want to run race gas.

He said he does not do the slide mod.

That is odd that Ken wouldn't do the head. I wasn't sure about the slide. Like I said I have always done my own. We're not talking about huge modifications here, this is fairly basic stuff. I have heard nothing but good things about Munn Racing, you could always give them a call. http://munnracing.com/# If they won't do the slide send me a PM and I'll cut it for free. If you are talking about the O-rings for the Head ? I have always just reused them, if only removing the head. I replace them with every top end rebuild though.


2/19/2018 4:01 PM

Thanks I actually figured out the orings are reusable.

He said dont cut the head unless your running race gas. Then he said the head should be at 50 thousandths which is about 1.25mm, so if mine is actually at 1.9 or 75 thousandths than I should be good on pump gas and getting it cut. I am going to do a squish test some time this week and see where I am at.

I really appreciate your offer and I may have to take you up on your offer if I can not find anybody. Im sure the rd-designs guy will do it but he has not gotten back to me and says he has like a month backlog or more right now on his website. I will email and call all the others. I did call slavens and they dont do motor work anymore. Sucks because they are an hr away from me.

If I could get all this done for around 100 ish bucks it would be well worth it.


2/19/2018 4:10 PM

Just another piece of info and please take it for what it's worth. I bought and raced and sold probably 100 bikes for Team Suzuki, Primal Impulse, Motoworld Racing, Bill Pipes from 98-05 and every RM250 that I got from 01-05 to race or to sell had the power jet disconnected and both plugs had silicon in them and they said that the RM250 ran better and easier to jet because it and that all of the riders tested and preferred it unplugged. Also they all had the cylinders lowered .030 and the heads cut to match and the squish was adjusted and these bikes ripped. I remember one of the engine guys saying that tightening up the squish changed the burn rate dramatically which made jetting the bike easier because of that as well.


2/19/2018 11:54 PM

lcgordon - Just to add re assurance, you can 100% trust what digger (and Digger29) is saying. digger is a very knowledgeable guy and helped me out a ton with jetting a while ago for my RM250.

Squish wise - my 08 was 1.38mm stock, I dropped it down to 1.28mm and noticed an improvement in the power and throttle resposne. The bike runs perfect with no issues at all. You will notice a massive difference in your bike going from potentially 1.9mm to 1.2/1.3mm squish.

Spend a few evenings and do some research into everything mentioned in this thread. It is time well spent and will allow you to achieve an engine and carb set up which will make your bike run awesome. It will make you wish you had done it all sooner!



2/20/2018 6:06 AM
Edited Date/Time: 2/20/2018 7:04 AM

RussB thanks a ton and appreciate the help. I trust what you guys are saying forsure. Plus reading the rb-designs website it seems like what I need to do.

For me its is kind of hard and I'm sure other people have kind of the same troubles, but the 03 was different than the 01-02 and different from the 04-07 and there is not a ton of 03 specific info out there. When there is everybody is at sea level so I can kinda use that info to help but I have to know I need to be leaner.

When researching I find a lot of contradicting info, and I'm sure nobody is out there trying to put out bad info but everybody has varying mechanical ability making it hard to see who really knows and who does not.

But this thread has been very good information and super helpful and I am excited to get this thing ripping.

Squish test will be done this week

Oh and one more thing somewhere around the 1.25mm I am still good to run pump gas right?


2/20/2018 9:20 AM

Just got an email back from Ron at RB-designs and I think I will go with him. He said he is at about a 1-2 week turn around. He said he can cut my slide also.

Just want to make sure I probably want 1.25mm (5300ft elevation on 91octane) and a 7.0 slide?

Cant wait to get this done I am super excited.


2/20/2018 11:41 AM
Edited Date/Time: 2/20/2018 2:05 PM

lcgordon711 wrote:

Just got an email back from Ron at RB-designs and I think I will go with him. He said he is at about a 1-2 week turn around. ...more

Yes, 1.25mm for squish and 7.0 for the slide. RB's accuracy in cutting the head is only as good as your solder measurements, so take your doing the measurements.

What Digger29 mention above about blocking off the power jet is a viable option. I bet 95% of the guys riding bikes equipped with a power jets would have know idea that the power jet wasn't functioning if it was blocked and disconnected. I have an 07' cr250 that uses a Keihin pwk with a disconnected and blocked power jet carb from a yz250, it works great. As far as I know KTM has never used a carb with a power jet on any of their 2T bikes, and everyone knows how well those bikes run when jetted correctly. All that you would need is a hex headed metric set screw, that you can get at any Home Depot, and to simply unplug the lead going to the power jet. Once the power jet is disconnected the power jet---jet/hole, located under the power jet plunger, the power jet unscrews like any other jet,will need to be plugged, or the bike will run overly rich. We are talking a couple of minutes of time and less than $1 for the hex screw. You don't need to remove the power jet solenoid.