CRF150, it is finished.

My over the winter project was to add, or try to add, 4 to 5 horse power to my 2003 CRF150F.

I am pleased to say the project is finally completed!

I added the following performance parts. Price of each in [ ] at the end.

Bore / hone. [$50]

JE Piston and rings, 12.5 to 1, with the dome milled down to make it 11.5 to 1. The .050 over piston makes the displacement 159.6 cc's to run in a class with max displacement of 160cc. [$180]

Ported the head. I didn't really make the ports larger, I just cleaned out the casting flaws and lines, and matched the intake manifold to the port. [$50 for the Dremel tool]

28mm Mikuni flat slide carb (TM28). This was a bear to get jetted, but after countless hours of trial and error, I finally got it. [$120, used]

Powroll performance camshaft. This cam has just a little lift, but quite a bit of duration, just what I wanted for the high rpm / high speeds of flat track racing. [$150]

Powroll Thrust Nozzle exhaust. [$30]

Various required gaskets and o-rings. [$50]

Total cost, $630. Would be about $700+ with a new carb.

But was it worth it? I believe it was. This little bike really came alive. Yesterday, after getting the jetting problem ironed out, I took it out onto a 1/4 mile oval short track to see what she'd do. I was running at about half throttle for a few laps, just to get things warmed up. My nephew pulled up along side me on his stock CRF150. We looked at each other and smiled. We boh twisted the throttles open at the same time, and by the time we reached the next turn 70 or 80 yards down the straight, I was at least five bike lengths ahead of him. After the next straight, I was 10 to 15 bike lengths ahead. What makes it better is that I weight 165 pounds, to his 100 pounds. So my little 150 really came alive with those $630 worth of mods. I then let my Nephew ride my bike, heck, I had a hard time getting him off of it. He was turning lap times 3 seconds faster on my bike as he was his, and a second faster then I was, probably because he weighs 60 pounds less then me. (I sure ain't going to admit he's a better rider then I am, even though he is). So ... if you have an extra 6-700 dollars, and enjoy making slow bikes go faster, I would suggest giving it a try.

Next on the list. Powroll oversized header pipe, and maybe, just maybe, mods to the CDI box (incorrectly called the rev box). If I can make or have someone make a CDI box that keeps the RPM below 10,000 but still have the advantage of the better ignition curve, I'm going to give it a try. If there are any after market ignition companies reading this that can make a CDI box do what I want, send me one, I'll test it out for you.

Sounds sweet, you dont have to run a race gas blend do you????

160 is legal in the 80/85 class isn't it??? making sure before i do anything to mine

Sounds sweet, you dont have to run a race gas blend do you????

Yes, the engine knocked a bit with 93 octane pump gas, so I'm using a 50/50 blend of 93 and 110 race fuel.

160 is legal in the 80/85 class isn't it??? making sure before i do anything to mine

I'm not sure about the rules in Indiana, but here in Illinois District 17, there is a class in flat track called the "86 to 160cc single cylinder four stroke only class". The CRF150 is the bike to have for that class.


How much is your race gas????

Hey Mike,

I have the 26mm carb on my 150, and the jetting has never been right. I ride Occatilla wells, and motocross tracks. It's great off the start, and full throttle, but if you back off the throttle, then put it on again it dies! Those are the simptomes! Any Idea's. The guy who tricked out my bike seams more than clueless. I have a 175 kit, the cr85 front and rear suspension all revalved. It just has that mid throttle bog!



If you are talking about the roundslide 26mm mikuni it is a totally different ballgame... I have had several people with that carb who would like to throw it away... honda 150 and ttr125 users alike... the 28mm mike38 has is a flatslide...

Good luck!


I am so happy you are happy with the bike... I have one more of those pistons sitting that I cannot decide what to do with... we will see!

See you in a few weeks!

How much is your race gas????

I bought two gallons of Polaris snowmobile race fuel for $8 / gal. :thumbsup: I'm looking for something less expencive asap.


lets see some pics man

Turbo blue 100 or 104 is fine.. your not running that high of compression... it should be around 4 bucks a gallon...

Sounds great... I'm actually looking to do something similar. Any intention of dyno'ing it to see how close you got to you HP goal?

One question... Where did you source your piston?



Mike got that piston from me... I had the pistons custom made... I have a guy I work with that worked at JE... he designed them...

I have one left... not sure what I am going to do with it yet...

If I could get enough interest I could make another batch order... I need 4 people minimum...

What are we looking at price-wise?

I don't think that it'd be too hard for me to come up with an order for four just from my circle of local friends...


I sent you a PM...

lets see some pics man

Sorry, no digital camera. Picture if you will, a CRF150 with flat track tires, 428 conversion, no front fender, no air box, and Flander's Number 10 handle bars. That's about it. The rest looks like a stock bike.


If you are talking about the roundslide 26mm mikuni it is a totally different ballgame... I have had several people with that carb who would like to throw it away... honda 150 and ttr125 users alike... the 28mm mike38 has is a flatslide...

Good luck!

Any word on why the 26mm sucks so bad? I'm seriously considering an 26mm XR200 carb for my wife's 175cc.

Tanks :thumbsup:

I have the same carb and am having problems what jetting specs did you use...


Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Similar Content

    • By jmathey9
      I have a 2006 CRF230 with an aftermarket exhaust. I want to bring it back to stock. 
    • By Euler Vaz
      I thought about using a 90/90/18 rear tire on the CRF230F to reduce unsprung weight, rotating mass and ground contact in order to optimize motorcycle performance. I use the crf230f for motocross. Do you think it would be a good change?
    • By 230F
      Jetting the 230F
      By: Phil Vieira
      This project takes no less than 2 hours if you have never done jetting to a bike before. It took me 1.5 hours, to take my bike apart, take out the needle, change my pilot jet and the main, and take pictures along the way, but I have seen the inside of my carb 3 times, so I know my way around it pretty well…
      You should be jetting this bike right when you get it home. This bike comes lean from the factory. If you don’t know what that means, it means that the bike is getting too much air, in terms, a hotter engine, and your plugs will get hotter, and a decrease in HP. To make your engine last longer, do this.
      These jetting combos are for a 2000 feet and below scenario. Any altitudes higher, you should do a search on the forum. If it cannot be found, post on the forum. Please don’t post on the forum “How do I do this…” You have all the answers here.
      This project comes to a grand total of less than 30 dollars. The needle is 20, the main jet is about 3 dollars, and the pilot is 5 dollars. You may not need to do the pilot jet depending on your situation, but again, if you’re riding 2000 feet and below, it’s a good idea to get a pilot jet.
      The jets I used consist of a 132 main, 45 pilot and the power up needle with the clip on the 4th position.
      Part numbers:
      16012-KPS-921 – Needle (Includes Power up needle, Clip, and needle jet)
      99113-GHB-XXX0 – Main jet (Where XXX is the size)
      99103-MT2-0XX0 – Pilot jet (Where XX is the size)
      For the Jets, just tell them you need jets for a regular Keihn carb, (also known as a Keihn Long Hex) main jet size XXX, pilot jet size XX. They should know the part numbers. For the needle, bring the number along. If you are lazy, they should have a fiche and they can look up the numbers. Then again you can take in the old jets, and make sure they match up to the new ones.

      Now, the tools you will need are as follows:

      ~A collecting cup of some sort. I used a peanut butter jar.
      ~Ratchets for the following sizes:
      - 6mm, 8mm, 10mm, 12mm
      - Extension for the sockets needed
      ~Phillips and Flathead screwdriver (Be sure these are in perfect condition. A badly worn screwdriver will strip the screws)
      ~Needle nose pliers
      ~”Vise grips” or known as locking pliers (Two)
      ~Open end wrench 7mm and 12mm
      ~ It’s a good idea to have a extra hand around
      (Not needed, but I highly recommend tiny Phillips and flathead screwdrivers (Pictured next to the jar and the ¼” extension) I recommend these for removing a couple things since you can put pressure with your thumb on the end and unscrew it with the other hand. This insures that you will not over tighten any parts, and ensure that you will not strip the heads of the bolts.
      Ok, now that you have the tools, let’s start by putting the bike on a bike stand. I put it on the stand rather than the kickstand because it’s more stable and sits higher. I hate working on my knees. Start by taking the number plates off. Yes, both of them. The right side, you take off one bolt and the top comes off of its rubber grommets, pull the top off, and the plate comes right off. The left hand side, use the 10mm socket to take the battery bolts off, and then take the Phillips bolt near the back. Again, rubber grommets are used to hold the top in place. Take the seat off. There are two mounting bolts on the back:

      Those two bolts are both a 12mm socket. Use the open end wrench on the inside, and use the socket on the outside. You may need to use an extension if you don’t have a deep socket. Once you have the two bolts off, slide the seat back, and lift it up. This is what you have. Notice there is a hook in the middle and a knob on the tank. That is what you are sliding the seat off of.

      Now that the seat is off, you must take the gas tank off. Don’t worry, you won’t spill any gas any where, I promise. On the left hand side of the bike where the valve is, slide down the metal clip holding the tube in place. Turn off the gas supply, and slip the tube off slowly. Now take off the two bolts in the front of the take. This is on the lowest part of the gas tank in the front, behind the tank shrouds. The socket you will use is an 8mm socket. Take the bolts all the way off and set them aside. Now look back at the last picture posted. On the back of the tank, there is a rubber piece connected to the knob and the frame. Slip that rubber piece off of the frame. Pull the vent tube out of the steering stem and lift the tank up. Don’t tip it, and lay the tank aside where you won’t trip on it. This is what you’ll end up with:

      It may be a good idea to take a rag, and wipe all the dirt off the top of the bike if any. You don’t want anything dropping down into the carb. If you do, engine damage is the result. A clean bike is always a good thing! Now we must drain the gas out into that container. This is very easy. Make sure you open the garage door, windows, whatever, to let the fumes out. Breathing this crap is bad. Here is where the drain screw is:

      (Don’t worry about removing the carb, that comes later) This is on the right side of the carb, on the float bowl. The vent tube that goes down to the bottom of the bike is where the gas drains to. Put the jar under that tube and start to unscrew that screw, enough so that the gas leaks into that jar. Once the gas doesn’t drip anymore, close the screw all the way. Now on to the top of the carb. We are going to take this cover off:

      This cover comes off by removing the two screws. Once removed, the lid comes off as well as the gasket. Flip it over and set it aside. Do not set the gasket side down on the ground, as it will get contaminants! Here is what you are facing:

      The angle of the camera cannot show the two screws. But one is visible. It has a red dot, and opposite of that side is a darker red dot. I made it darker because it’s not visible, but that is where it is. This is where I use the miniature screw drivers to get the screws. I magnetize the screwdrivers, and use care to make sure I don’t strip the heads. Metal pieces in a piston are not good! Remove the two screws. Put these screws on a clean surface so they do not get contaminants. Now get your vise grips and set it so that it will lock onto the throttle, not too tight, not too loose. Set the vise grips on the seat. Start to open the throttle slowly as you guide that “plunger holder” (as I call it) up to the top. Once you have the throttle all the way open, take the vise grips, and lock it so that the throttle does not go back any more. What I do is I hold it pinned and lock it up against the brake so it doesn’t rewind on me. If you don’t have locking grips, a friend will do, just have them hold the throttle open all the way until you are finished. How fold the plunger holder to the back of the carb and pull the piece up to the top. Take care not to remove it, as it is a pain to get back together! If it came apart on you, this is what it should be assembled to:

      Once you get the holder out of the slider, set it back like this:

      As you can see, the bar is back 45 degrees, while the holder is forward 45 degrees to make a S. Here is what you are faced with when you look down on the carb:

      Where the red dot is where the needle lies. Grab needle nose pliers and carefully pull up the needle out of its slot. This is what the needle looks like once it is out.

      Now we must move the carb to take the bowl off. Untie the two straps on the front and back of the carb. Don’t take them off; just loosen them until the threads are at the end. Take the front of the carb off the boot and twist the bowl as much as you can towards you. Tie the back tie down to that it does not rewind back on you. This is what you have:

      Now we must take off the bowl. Some people take that hex nut off to change the main jet, which you can, but you cannot access the pilot jet, and you can’t take out the needle jet (a piece the needle slides into), so we need to take it off. It’s just three bolts. As we look at the underside of the carb, this is what you will see:

      The bolts with the red square dots are the bolts you will be removing. These are Phillips head bolts, and the bolt with the blue dot is your fuel screw. This is what you will adjust when the time comes, but keep in mind where that bolt is. You need a small flat blade to adjust it.
      Well, take those screws off, and you are faced with this:

      The blue dot is for cross reference, which is the fuel screw once again. The green dot is the pilot jet. You can remove this using a flat blade screwdriver. Just unscrew it and pull it out. Once you pull it out, set it aside and put in the 45 pilot jet you got. The red dot is the main. You remove this by using a 6mm socket. Just unscrew it. If the whole thing turns, not just the jet, but the 7mm sized socket under it, don’t worry, that piece has to come out as well. If it doesn’t, use a 7mm to unscrew it off. Here is what the jets look like:

      Pilot Jet

      Main jet attached to the tube. Take the main jet off by using an open end wrench and a socket on the jet. Again, it screws right off.
      Here is what you are faced with if you look form the bottom up.

      From left to right: Main jet, Pilot Jet, Fuel screw. Now in the main jet’s hole, if you look closely, you see a bronze piece in the middle of that hole. We are going to take this off. Since I did not do this part (I only changed my pilot jet when I took these pictures) there are no pictures taken for this section but this is really simple to do if you’ve been a good student and know where things go. You should know anyways, you have to put the bike back together!
      (Notice: There have been discussions about these needle jets being the same. Only change this needle jet if the one you have is worn out. If you do not have the old needle, a older drill bit bigger than 3/20ths (.150), and smaller than 11/100 (.11") Use the tapered side of the bit, set it down in the hole and tap it out carefully.)
      Now take your OLD needle, I repeat, the OLD needle because what you are going to do next will ruin it. Pull the clip off with your needle nose pliers, or a tiny screwdriver to pry it off. Then put the needle back in the hole where it goes. That’s right, just to clarify, you took off the needle, and you put the needle back in the hole with no clip. Slide the point side first, just as it would go normally. Now if you look at the bottom of the carb, the needle is protruding past the main jets hole. Grab another pair of locking pliers (vise grips as I call them) and lock it as tight as you can on the needle. Pull with all your might on the needle. Use two hands. Have a friend hold the carb so you don’t pull it off the boot. Tell them to stick their fingers in the hole that goes to the engine, and pull up. After pulling hard, the needle jet should slip right off. Then notice which side goes towards the top of the carb. There is one side that is a smaller diameter than the other. Take the new needle jet, and push it up into the hole the way the old one was set. Just get it straight. Take the tube the main jet goes into, and start threading it in. Once you can’t tie it down anymore with a ratchet, unscrew it and look at the needle jet to make sure it’s set. That’s it for the needle jet. Now let’s start putting the carb back together.
      (Notice: Many people have destroyed jets and such by overtighting them! Use the thumb on the head of the wrench and two fingers on the wrench to tighten it down.)
      Thread the main jet into the tube it goes into, and then start putting it back on the carb. Thread the pilot jet in as well if you haven’t done so already. Remember these carburetor metals are soft as cheese, so don’t over tighten the jets very much. What I do is I put my thumb on the top of my ratchet, and use two fingers closest to the head of the ratchet to tighten the jet. That’s how tight I go when I tie them back in.
      Now before we put the carb back together, let’s adjust the fuel screw. Take a small screwdriver, and start screwing in the fuel screw until it sets. Again, do not over tighten, just let it set. Then count back your turns. Count back 1.75 turns.
      Now we must put the bowl back on. The white piece that came off with the bowl goes back as followed:

      If you look directly under the carb, the round hole is aligned with the pilot jet. Take the float bowl, and put it back on.
      Untie the rear clamp and the front clamp as well. Slip the carb back the way it used to. Make sure that it is straight up and down with the rest of the bike. The notch on the front boot should be aligned with the notch on the carburetor, and the notch on the carburetor should be in that slot. Tie the clamps down securely.
      Let’s put the needle in. These are how the needle numbers go:

      The top clip position is #1, the lowest one, closest to the bottom, is #5. (The picture says six but it is five in this case) For reference #1 is the leanest position, while 5 is the richest. I put the clip in the 4th position. Read at the bottom of the page and you can know what conditions I ride in, and you can adjust them to your preference.
      Put the clip in the new needle, slip it in. Take the vise grips off your grips and start guiding the plunger holder down to the bottom. Remember not to let that assembly come apart because it is a pain in the ass to get it back together! Once you get it to the bottom, put the two screws on, and then put the cover on.
      Now that you have done the carburetor mods, there is still one thing you want to do to complete the process. Don’t worry, this takes less than a minute! On the top of the air box there is a snorkel:

      As you can see, you can slip your fingers in and pull it out. Do that. This lets more air in to the air box. Don’t worry about water getting in. There is a lip that is about 1/8” high that doesn’t let water in. When you wash, don’t spray a lot under the seat, but don’t worry about it too much.
      The next thing you must do is remove the exhaust baffle. The screw is a torx type, or you can carefully use an allen wrench and take care not to strip it:

      The screw is at the 5 o’clock position and all you do is unscrew it, reach in, and yank it out. This setup still passes the dB test. The bike runs 92 dB per AMA standards, which is acceptable. Just carry this baffle in your gear bag if the ranger is a jerk off. I’ve never had a problem, but don’t take chances.
      That’s it! Start putting your tank on, seat, and covers. After you put the seat on, pull up on the front, and the middle of the seat to make sure the hooks set in place.
      Turn on the bike, and take a can of WD-40. Spray the WD-40 around the boot where it meets the carburetor. If the RPM rises, you know you have a leak, and the leak must be stopped. You must do this to make sure there are no leaks!
      Here is my configuration:
      04’ 230F
      Uni Air filter
      132 Main Jet
      45 Pilot Jet
      Power up needle, 4th clip position
      Fuel screw 1.75 turns out
      Riding elevation: 2000ft - Sea level
      Temperature – Around 60-90 degrees
      Spark Plug Tips
      When you jet your carb, a spark plug is a best friend. Make sure your spark plug is gapped correctly, (.035) but that’s not all that matters. You want to make sure the electrode is over the center, and you want the electrode to be parallel, not like a wave of a sea. Put in the plug, and run the bike for 15 mins, ride it around too then turn it off. Then take off the spark plug after letting the bike cool. The ceramic insulator should be tan, like a paper bag. If it is black, it is running rich, if it is white, it is running lean. The fuel screw should be turned out if it is running lean, and turned in if it is running rich. Go ¼ turns at a time until your plug is a nice tan color.
      Making sure your bike is jetted correctly
      While you are running the bike for those 15 mins to check the plug color, you want to make sure it’s jetted correctly now. Here is what the jets/needle/screw control:
      0- 3/8 throttle – Pilot jet
      ¼ to ¾ throttle – Needle
      5/8 – full throttle – Main jet
      0-Full – Fuel screw
      Pin the gas, does it bog much? Just put around, is it responsive? When you’re coming down a hill, the rpm’s are high and you have no hand on the throttle, does it pop? If it pops, it is lean and the pilot jet should be bigger. If it’s responsive your needle is set perfectly. You shouldn’t have to go any leaner than the 3rd position, but I put mine in the 4th position to get the most response. Your bike shouldn’t bog much when you have it pinned. If it does it is too rich of a main jet.
      Determining the plug color, you will have to mess with the fuel screw.
      That’s it, have fun jetting, and any questions, post on the forum, but remember to do a search first.
      Also, if your bike requires different jets due to alititude, humidity, or temperature, please post the following so we can better assist you:
      Average temperature
      Altitude (If you do not know this, there is a link in the Jetting forum that you can look up your alititude)
      Average Humidity
      What jets you are currently running
      What the problem is (If there is one)
      Just do that and we'll help you out the best we can.
      EDIT: The girl using this login name is my girlfriend. You can reach me on my new login name at 250Thumpher
      Then again, you're more than welcome to say hi to her!
      -Phill Vieira
    • By jason230
      Well I figured this would be a cool thread to have seeing as how quite a few of us have gotten pretty far into upgrading our 150/230s. This will be helpfull for those looking into getting things for their bike so they can see what everything looks like.
      '05 CRF230:
      -Acerbis Rally brush guards
      -Factory FX #'s
      -Renthal 7/8ths MC bend w/ soft half waffle grips
      -BBR +1/2" shift lever
      -BBR revbox
      -White Bros. R-4 Full Exhaust
      -Twin-Air and White Bros. airfilters
      -White Bros. 112main and 48pilot jets
      -Dunlop D756's w/ MSR Ultra Heavy Duty tubes