Porting & Head work

Bought my 03 RM250 new and after getting the jetting close to actually working (a real pita on the 03s) I still had a hard time dealing with the big mid-range hit when riding in these Ozark Mountain rocks.

I called Varner Motorsports because I knew they were doing the motor work at the time for Suzuki Off Road (Smith, Kiedrowski and Hatch.) After reworking the head (I insisted on 92-93 octane only), shaving some material off the base of the cylinder, and porting work, it worked much better in the tight slippery stuff. Terry Varner insisted I stay close to my previous jetting specs, but it seemed too rich. Maybe because I only go 160 lbs, maybe because I short-shift and use the torque of the motor I'm rarely putting a big load on the bike like Team Suziki would, maybe Mr Varner was being overly cautious with his jetting recommendations...?

I've done searches within this forum and before my motorwork I was right where most of you are with jetting on the 03s, but after the cylinder and head work I'm always 1-2 sizes leaner with the pilot, JD red needle in recommended 4'th slot until over 70* (then I go to 3'rd slot), usually a size leaner on the main too.

Ever hear of having to lean things out when porting/head work is done? I guess it's because the motor is breathing better?

Usually porting, raising compression/ head work or a pipe require leaner jetting as the motor is more effecient pump, pumping more fuel. He probably said stay with your old jetting as thats a good baseline, and safer than saying lean it out immediatly. How does your plug/ piston look? That is the true answer.

My 03 has previous porting work before I bought it. I'm not sure what was done, you can see the ports were worked on/ altered and the cylinder has a code scratched in, but who and what was done is unknown to me.

Anyways I'm always a little leaner than most here with my jetting as well, except the main were I'm usually a step fatter.

But in the summer I run a 42 pilot and stock needle 2nd clip.

Every bike is a little different, just use suggested jetting as a baseline and tune your bike from there.

On a different note when I had my WR450 flow ported I had to go way richer with my jetting, the techs recomended my previous jetting. I did change pipes and exhaust cam as well though.....

Just goes to show every motor is different.

Plug's light brown through the low and mid. I tune the main to look skin color fully warm and WFO under a load, then play it safe and go one step richer with the main. Piston crown shows signs of carbon, but not much... 80 hrs out of a top-end w/ a re-ring at 40 hrs.

80-100*F

1000-1500 altitude w/ Midwest humidity

p- 40

m- 165

Varner got good torque and low-end out of this motor, with a real big, late-midrange rush. :busted:

Plug's light brown through the low and mid. I tune the main to look skin color fully warm and WFO under a load, then play it safe and go one step richer with the main. Piston crown shows signs of carbon, but not much... 80 hrs out of a top-end w/ a re-ring at 40 hrs.

:

Sounds like you have nothing to worry about :busted:

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