Baseline jetting RM250 P 1993

[hal]

Hi. Just bought myself a 1993 RM250 P. I'm a long time motorcycle rider and quite good with 4-stroke v-twins, but I'm new to dirt bikes and have never tuned a 2-stroke before. When I got the bike it were almost impossible to start, due to a too low float setting. I set the float height to 16mm and now the bike starts easily but doesn't run quite like I think it should.

It runs like crap for a few minutes before it's warmed up properly. ( I guess it's supposed to? ) When well warmed it runs better, but the powerband seems very narrow. Midrange is strong but it won't rev much. It does idle when warm.

Current jetting in the Keihin PJ38 carb: Main- 200, Slow- 45, Needle- R1471N (DGM) in 3rd slot from top, Air screw- 1.0 turn out. I'm running a NGK BR8EIX plug. It's black, but doesn't foul up. I'm thinking that main jet is too big but I don't know what size to try. (Don't want to buy 50 different sizes)

Does anybody know the original baseline jetting for this bike? Anybody have a set up that works good? Engine is stock as far as I know. Elevation approx 400ft.

All tips will be appreciated!

 

[Todd Derossett]

Jetting

The 93 RM250's come really rich from the factory. I remember a friends 93 I used to borrow and race. Try the following and it should clear up the jetting a make it a lot easier to start.

Main Jet: 178
Pilot: 55
Needle: stock w/clip in the middle
Air screw: 1 1/2 turns out.

As far as the bike having a lot of midrange and not much top that was the nature of the engine that year. Two things will help out a little. Purchase a pipe (Pro circuit or FMF) and loosen the two screws on your powervalve on the side of the cylinder and turn the valve to the 11o'clock position which adds tension to the spring and will help the bottom end some.

Good Luck!

 

[hal]

Thanks Todd :moon:

 

[snb73]

Hal,

I have a 93 RM-250 also. I live in southern Maryland, I'm less than 500 feet above sea level. Here is what I run. I've had the same plug in my bike for 6 months so far.

Spark plug NGK-BR8EG

Pro Circut Platinum pipe w/ 304 silencer

Boysen Pro Series Reeds

Current Jetting
Main-180 RD
Pilot- 52
Needle- R1471NS #2 position, one lean from center
Air Screw- 1 ½ turns out

I strongly suggest you take the carb apart and clean it. 2-3 cans should do it. While the carb is off, remove the reed cage and check for splits, cracks or warping. Replace the silencer packing too. Check to the preload on the exhaust valve spring, should be one full turn clockwise. Todd's and my jetting and may not work for your bike, but it's a starting point.

Hope this helps, Steve.

Check out Eric Gorr's site on jetting.

http://www.ericgorr.com/techarticles/carbtuning.html

 

[hal]

Got my new jets today. 178 main and 55 pilot. Set 1.5 turns on air and keeping needle in middle slot. WOW. Bike went from moped to wheelie monster! Unbelivable what a couple of little jets can do.

Makes me wonder... If the 200 main and 45 pilot jets were original. How many of theese bikes has never run properly in their lifetime???!!

Thanks guys for helping out!
Hal

 

[snb73]

add info

Hal,

Sounds like a previous owner tried to jet it, and went the wrong way. My "Clymer" manual sayes the stock jetting for a 93 RM-250 is;

Main 180
Jet Needle - R1471NS - 3rd clip
Slow Jet - 45
Air screw 1 1/2 turns out

Glad it worked for you, have fun. Steve

 

[Todd Derossett]

Glad your bike is running better. The stock jetting was a 200 main and a 45 pilot. Back when I was in college and a friend of mine bought a brand new 03 rm250. He had the same problems with the jetting being rich on top (the pilot was actually lean). I rejetted his bike (with a little help from fmf )and it ran perfect. Since I had to sell my bike at the time to finish school he let me race his bike a few times. I never raced a 250 before and I got 2nd place my first time.

To fine tune your bike a little more you can play with the with the air screw a little. Set idle a little high and turn the air screw in until it the rpm's start to lower and then turn it back out until it idles at the highest rpm. You shouldn't turn the screw past 2 turns out since it doesn't really do much past 2 turns. Once you have this adjusted turn your idle back 1/2 turn just past the point where it doesn't idle. 2-strokes don't need to idle(unless you want it to). On morinings or cold days you can also turn the air screw in 1/2 turn and as the day warms up turn it back out. If you have any questions let me know!

Todd Derossett