Jetting specs for 03 RM250

[tonyromero]

Merry Christmas everyone, I just rejetted the RM. I am using a 45 pilot, stock needle 3rd clip from the top and a 185 main. It runs much better than it did before however its still not right. From idle to about 1/3 throttle it hiccups and doesn't rev smoothly. I'm not sure if its getting too much fuel or not enough. The stock pilot was 50, I turned in the air screw 1/2 a turn to fatten the pilot up a bit just in case a 45 was overkill but it didn't seem to help. In retrospect I wish I would have made the changes one at a time so I could see the effect of each. The top end feels fine so I think the main is ok. The plug looked correct when I pulled it out after a couple of drag races down the block. any ideas? Could it be that the bike just runs that way low end? do any of you have smooth revs on low end? help

 

[Studboy]

If it is jetted right it will have smooth revs on low end.
Is your bike bogging or sputtering?

 

[tonyromero]

Ok, so I tested out my new setting today. I went to a 185 main, 45 pilot, and dropped the stock needle one clip. The bike revs well in the upper rpm range and the plug was a nice tan color, however, from idle up to 1/4 throttle the bike still sputters and coughs. I am at a loss as to what it could be. It did the same thing with a 50 pilot and a 45 seems to make no difference. Could there be something other than the slow jet causing this? I am using a BR8ES plug and mixing at 36:1. The spooge was significantly reduced with my new jetting however. Could it be that I am so used to my DRZ and a 4 stroke powerband that I don't realize maybe the RM is supposed to sputter early in the RPMs. Please tell me I'm wrong and the bike revs cleanly at low RPMs when dialed in. If anyone can tell me what to change to get it right I'd appreciate it.

 

[tonyromero]

sorry, I posted twice because I did't see my original post appear. The bike is sputtering not bogging. It sputtered with a 50 pilot and with a 45. I thought I may have gone too lean with the 45 so I compensated by using the air screw to reduce the air which would have the same effect as increasing the fuel but it didn't help.

 

[Studboy]

I would try and go to a 40 pilot jet. What altitude are you at? I am assuming close to sea level since you are in Florida. Is it smoking and brap brap brapping at 1/4 throttle or is it when you give it the gas it bogs like "bwaaaahhh"? You won't hurt anything by trying a leaner pilot jet.

 

[tonyromero]

A 40 ? hmm. I read the Nov. issue of Dirt Bike and they are at 1000 ft over sea level and they are using a 48 pilot, a 175 main with great results. I can't imagine I would need an even leaner jet at sea level. A guy up in West VA is using the 45 pilot with good results, although he is using a completely different needle. Since i don't have a leaner pilot jet handy maybe I can go a full 2 1/2 turns out on the air screw to lean it out more. What a pain in the ass this is. I wish I had gotten a WR450 or 250.

 

[Pacho]

Tony, it sounds like your fuel/air mixture is still too rich. The '03 RM 250 bogs and sputters when rich and makes a loud pinging noise when lean.

Here in SoCal (MX, sea level, 60F, 50% humidity) I am using a 175 main jet, stock needle with clip in the 2nd position (starting from the top), stock slow jet and 2 turns out on the air screw. It sputtered and bogged with the standard settings but it is almost perfect now. Perhaps it bogs a bit when the temperature gets warmer and I can probably fix it with a smaller slow jet.

I am sure you get warmer and more humid weather in Florida (75F, 75% humidity at the least) which means less oxigen and requires leaner conditions. In addition, trail riding usually requires leaner jetting. The easiest experiment is moving the air screw and if it's not enough, further move the needle clip and/or change the slow jet. Pinging and spark plug tan will let you now when it gets too lean.

Check this site for good information on how weather, riding conditions and others affect jetting performance: http://www.eric-gorr.com/twostktech/carbtuning.html

Good luck!

 

[Pacho]

1000 ft. can make a difference. Try 2 1/2 turns out and move the needle clip if needed.

 

[Luft]

Try running the 45 with the air screw out at 1-1/2 turns. Ride around for about ten minutes and open the throttle to test the setting under load and current air temp and pressure. Open the air screw more to lean the pilot circuit 1/8 to 1/4 turn at a time. If you go over two turns try the next size lower pilot jet and begin at 1-1/2 turns out. Gradually turn the air srew out until you are satisfied. With the 40 pilot you might also turn the airsrew in to richen the pilot mixture for even better performance. You have more humidity than Cali which makes the air less dense causing settings to be richer. Pacho, if you are at 2-1/2 turns out you might try the next leaner size pilot and begin with 1-1/2 turns out on the air srew. If this is too lean you can turn in on the air screw to richen.

 

[los36]

There were many threads concerning the RM's very low RPM response when the '02s came out.
One thing that some people experimented with was leaning out the slide cutaway. Either by buying a new or cutting the stocker.

 

[tonyromero]

Ok. took the bike out today and it ran pretty good as is. I think it was sputtering not because of my jetting but because I was not quick on the throttle. When I really gave it the gas it revved cleanly and crisply throughout the range. Fast bike. However, for my purposes I think I"d have been better off with a big 4 stroke. The reason is I ride lots of long dirt roads and the RM, although it accelerates nicely, cannot be held in 5th gear wide open for more than a few seconds. It is made for MX and a series of short bursts which is not the type of riding I do. Silly me. Too bad, I was really starting to get used to it and like it. Maybe the KTM300 will be better for me or maybe the WR450.

 

[Luft]

Now you need to work on the gearing. Try 1 or 2 smaller teeth on the rear sprocket to spread out the power.

 

[Jawsrm134]

Tony,

The 45 pilot is fine, There is a little miss down low that is documented. I rejetted mine and its graet. I also put a 12 tooth sprocket up front for the woods and I have had no trouble. It carves through the woods way better than my DRZ ever did. 45 pilot needle 3rd clip from top air screw 1 1/2 turns out and 185 main jet. I called carbparts and they said that Decosters brother just ordered 36 7.0 slides for the PROs bikes. The stocker is 6.0. Im not going to purchase one right now, my bike runs great. Remember the 2 strokes are ging to be a little funny down low, as long as its not fouling plugs and loading up its fine. I dont ride 5th gear wide open so thats another problem all together.

Mark

 

[tonyromero]

I really like the bike except for the low top speed. How much will it effect the top speed if I go 1 tooth larger on the front sprocket? Or perhaps is it wiser to go two teeth smaller on the rear? would the effect be the same? I don't think I would have an issue with 5th gear full throttle if at that time I was doing 80mph. I am still toying with the idea of a flyweight and the FMF gnarly pipe. For now I just want to get the gearing right and see if I can come to terms with the bike. I really like it, I simply have to have more top speed though.

 

[gbs1]

toneyromeo,
I just came back from Florida and raced at Gatorbacl all wekend and was running the the jetting I told you about early in the post it ran clean and crisp and the other rider using the RM almost holeshot every race he was in which was 3 classes.(he is an expert rider) We had 8 moto on it in 1 day. Part of your problem is in the needle and the main you got the pilot going in the right direction.

 

[02'Cr Rider]

gbs1, My 03'rm runs great,but it spooges like its very rich as you mention earlier.The plug looks good,but has black oil all over the place.I ride it hard so that shouldn't be the problem.In the dec. 2002 dirt rider mag,they run a N3WJ-2nd needle,will this needle help me out?What is everyone carb settings?I want to get rid of the spooge.Please help

current settings
1500ft.
32:1 mxt2 w/91octane
stock needle@2nd from top
180 main jet
45 pilot
1 1/2 air screw