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1987 250R

Carb: Keihin 38mm Air Striker

Main jet: 175 (plug chop confirms a tad rich, close enough to run hard for long stretches and be on be safe side)
Runs hard and clean

Slow jet: 48

Needle: Keihin DDJ on first/top/leanest clip

Air screw: 2 turns out

Intake: CFM aluminum airbox with no cover; stock '87 carb to airbox boot; Twin Air foam filter with Maxima oil; UPP oversized intake boot

Reeds: VForce 3 reed valve

Exhaust: Pro Circuit Platinum pipe, Pro Circuit 304 silencer; o-ring BDT billet pipe flange; all joints sealed with HondaBond

Engine: BDT MX ported stock cylinder at 66.5mm (250.07cc); compression set for race fuel

Ignition: 2000 CR250R ignition system

Fuel: Sunoco purple 110 mixed with Maxima 927 oil @ 32:1

Elevation: 1,000-2,000 ft above sea level

Temp range when jetted: 60-80 degrees

The bike runs smooth and clean. Very responsive. No flat spots, no hiccups. Starts 1st kick hot or cold, with or without the choke. I feel like it's spot on. I hope this helps somebody.




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I have a problem ive been trying to figure out my carb settings an was hoping to get some idea of what i should do i just bought a 38mm airstriker carb on my 86 250r an it has a fmf fatty pipe an v force reeds an a uni air filter don't know if i should port it or not, I bought the carb because it had a round slide carb an was like a 34mm, an just felt like it had bad throttle response an I wanted to get it to have a little more power, I'm 100ft above sea level an temp is usually around 70 75 , thank you, any info helps i appreciate it
 

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I would buy a bunch of NGK BR9ES plugs ( their under 3 $ apiece ) or BR8ES which are 1 step hotter than 9. Then start plug choppin. I would start with at least a 175 main jet. Don't want to run it lean at WFO. If that's to big work your way down. Really you need to do plug chops at mid range and low range to get your carb totally balanced. It takes a lot of plugs usually. You can get lucky though. I went through a dozen plugs on my last carb tune session. But I did low mid and high. Don't be afraid to put in the jets it wants. I'm running a 30 pilot jet. Sounds crazy but that's what it wants. 162 main, and my needle is in the second position. This engine doesn't like a lot of fuel for some reason. But that's a good thing I guess. So find a long nice dirt road where there's no damn cops, and start choppin.
 

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Jetting Help

I have a 86 250r bored 20 over an ported cylinder I have vforce reeds fmf gold series fatty pipe an fmf muffler an a 38mm pwk carb I got a jd jet kit blue needle 3 clip (middle) air box is still all together with lid main jet i put in there is a 175 an a 45 pilot I ride at sea level, I'm still putting the engine in it so I haven't started it just was wondering if that jetting sounds good or should I drop it to a 170 or 165? An the 45 is all they gave me in the kit, any info will help thank you
 

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I have a 86 250r bored 20 over an ported cylinder I have vforce reeds fmf gold series fatty pipe an fmf muffler an a 38mm pwk carb I got a jd jet kit blue needle 3 clip (middle) air box is still all together with lid main jet i put in there is a 175 an a 45 pilot I ride at sea level, I'm still putting the engine in it so I haven't started it just was wondering if that jetting sounds good or should I drop it to a 170 or 165? An the 45 is all they gave me in the kit, any info will help thank you
blue needle? Sounds like fake jets/ counterfeit.. Not keihin setup
hopefully works
keep 175 if doesn't run good check plug before drop may need more
 

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The blue needle is for sea level an red is for higher like mountains, just the tip is painted not the whole needle, it's jd jetting look them up there supposed to be like the top of the line jetting, but thank you
 

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Figured I'd post my old motor specs on here. Been a while since someone has. Switching to 363 this year so this tried-and-true setup will be no more but worked perfect for 2 years XC racing. Tad rich all around but internals looked fantastic whenever I had it apart. No matter what I jet, seems the dryer, warmer air here in the Dallas-Fort Worth area likes leaner jetting than most other comparable places elevation-wise. Optimum performance jetting on this is probably a 42p, 172m above 70 but I prefer to be a tad rich and keep the guts together longer.

Mixture ratio and fuel: 32:1 Klotz w/ Sunoco 110

Carb Type: Mikuni, Keihin (PJ, A/S, etc.) (what bore is the carb?) 38mm PWK

Main Jet size: 175 above 70 degrees here in Texas, 178 below 70 degrees

Slow (pilot) Jet size: 42 above 70, 45 below 70

AirScrew (number of turns out): 1

Needle (what groove is the clip in, Brand, etc): DGH 3rd slot

Reed brand and type: Boysen RAD valve, carbon fiber reeds

Airbox: stock box, no lid, UNI filter

Pipe: CT mid, FMF silencer

Engine Displacement: ESR310PV, 72.25mm bore, 4mm stroker crank

Compression ratio: 210psi

Porting type: TRX7 woods

Altitude: 500' - Texas
 

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My '86 does the same, bog a little on the bottom, then takes off. Fmf slip on, 35mm AS, K&N filter, stock 66.50, 175 psi compression WOT, Alabama 222' elevation. I set mine to 48 pilot, 150 main, 2nd clip, 1 3/4 turns out. I had it tuned by a motocross mechanic, but I can only tell a slight difference. Perhaps its just me trying to drive it like a 4 stroke.
 

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Hey guys

Stock 1986 engine all original has 15 hours ride time total.
Mods: fmf fatty pipe, turbine silencer, vforce 3 reeds, no air box lid, k&n style air filter.
89 pump gas mixing 32:1 dominator oil.
The carb is stock running 150 main , needle is 2nd position, stock pilot jet.
Starts first kick every time idles very well no issues.
I've got a bog at wide open throttle 5th and 6th gear. She will fall flat on her face throw you ovef bars.
Elevation unknown Louisville KY

Need advice please
 

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Hey guys

Stock 1986 engine all original has 15 hours ride time total.
Mods: fmf fatty pipe, turbine silencer, vforce 3 reeds, no air box lid, k&n style air filter.
89 pump gas mixing 32:1 dominator oil.
The carb is stock running 150 main , needle is 2nd position, stock pilot jet.
Starts first kick every time idles very well no issues.
I've got a bog at wide open throttle 5th and 6th gear. She will fall flat on her face throw you ovef bars.
Elevation unknown Louisville KY

Need advice please
Clogged main jet?
 
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