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I called up PRO CIRCUIT today and they told me for a stock 2005 R use the following:

MAIN: 162

PILOT: 42

NEEDLE: NCYR 3rd from top

FUEL SCREW: 2 turns out

LEAK JET: 55

What does everybody think about this?

Where do you live and what altitude?

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I took PCs advice and did their jetting specs exactly. The bike rips. I have a Ti-4 slip on. At first I did everything but the leak and it ran OK. Then I switched t the 55 and it ran even better. I think PC knows a thing or two. Just do their specs, you'll be pleased.

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I live on the east coast. Connecticut. I am probably just a hair over sea level. I told them I had the stock pipe ( furnace)on. Stock main is 72 and honda gave me a 75. I thought 62 sounded lean too. The bike backfires now and bogs a bit. Does the jetting change if you remove the backfire screen. Do I need it. It bends easily.

Thanks for all your help guys!!! :cry:

Hey Throttlejockey, where are you? I am in Oxford. Where do you ride?

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I removed the backfire screen (bent a few metal tabs and retained the plastic frame). The bike has A LOT more bottom end. I'm going to try a richer main jet next weekend. I think that removing backfire screen leaned out the carb and I can probably obtain even greater results by going richer.

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crf250x 1994 at 4,000 feet, and I'm still trying to de-bug the jetting. I just put a 125 main, 3 clicks from the top on the needle, 1 1/4 out on the fuel screw and I just ordered a #42 pilot and hoping it will work. Where is the pilot located? Is it under the main? What's the best way to get to it? Is there any special tools needed?

Hey thanks for anyones assistance and heck once it works we will have a setting for 4,000 feet.

If someone has figured this one out...share...share...share

Thanks...Bogger

Ok, I just moved the needle up second from the end and it's running much better, the fuel screw is out 3.25 turns, but I think the 42 pilot is still in order...it should be here today...I might have to go up to a 128 main.

Well I installing the 42 pilot wasn't that bad and no you don't have to take off the bowl, which I did anyway. I went up to a 135 main, 42 pilot, second from the bottom on the needle, and 3 turns out on the fuel screw. The front end is now coming up in second gear like it should. I still have just alittle hesitation just after idel when you hit it hard. I probably need to try a 138 or a 140 main which I have to buy tomorrow. Man I'm going to have a full collection of main jets. If anyone has any suggestions let me know.

Thanks again...soon not to be BOGGER.

I got it....with the above setting and a 152 main...it's like right on....no wonder everyone is having valve problems, the heat generated with lean setting has to be weighing heavy on the valves. I can't believe Honda hasn't done anything about it. Good Luck....Jim

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CRF250X 49 State

4500 Elevation Northern CA (Bought in RENO, NV)

Thumper Racing 270 BIG bore kit

Power NOW Plus Kit

R CAM

R Header

Air Box mod

Twin Air Filter and cage

Muffler Cork removed

Pink Wire

165 Main

145 Pilot

R Needle top postion

#70 Jet Leak

When it hits the cam, HANG ON! BUT, some what disappointed in the low end. May go back to stock cam and header. Maybe HOT CAMS will come out with something better :cry:

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Does the pilot jet control low end response?

What is the function of the leak jet?

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quick question a friend of mine has a 140 main and a 42 pliot and I want to go with the same but only could find a 45 pliot and 140 main in town how much will this change from his also what is a leak jet?? Thanks for the help

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First, the bottom end means the throttle closed. Not the speed of the bike or the RPMs of the engine. If you lug up a hill at low RPM but full throttle, it is not the bottom end for jetting descriptions. The throttle closed to 1/8 throttle position is controlled primarily by the pilot circuit. The pilot circuit is the pilot jet and fine tuned (after selecting the right pilot jet) by the fuel screw (aka pilot screw) in the bottom front outside of the carb.

For completeness, the midrange (throttle from 1/8 or so to just over 1/2 open) is controlled primarily by the needle taper and clip position. The full throttle or Wide Open Throttle (WOT) is controlled primarily by the main jet. For nitpickers, the throttle slide cutout is also a big factor in the throttle nearly closed position.

This is how I envision it, smarter people may clarify this, but with the throttle closed, there is high intake manifold vacuum in the front (cylinder side) of the carb. This is because the cylinder trys to suck in air and the carb slide is mostly closed. The pilot circuit is in the front of the carb, you'll see this because the fuel screw and pilot jet are toward the front and when you clean the carb, squirting carb clearner in either comes out in front of the slide. So when the manifold vacuum is high (higher the more closed the throttle), the manifold vacuum pulls fuel up the pilot circuit and feeds the engine. As the throttle opens, the manifold vacuum drops and the pilot circuit supplies less fuel. In fact, as the throttle opens, two factors make the pilot circuit less of a factor, the manifold vacuum drops and the fuel coming through the main jet is very large compared to the fuel the pilot circuit flows.

Most carbs have a butterfly valve that lets air through the carb as you open the throttle. The flat slide is more like a guillotine that opens as you open the throttle. There is a needle, maybe 4 inches long and tapered that slides down the flat slide and into the main jet. When the slide is closed, it either completely or almost completely blocks the main jet. As the throttle opens, the tapered needle pulls up out of the main jet allowing more and more fuel to be drawn into the carb. Both the needle and the slide open together. At some point, the needle is entirely out of the main jet and it doesn't get any larger with more throttle position. At this point to WOT, the main jet is the only control of the main circuit.

The main circuit is made up of the main jet (in sizes from 130ish to 180ish), the size and shape of the needle, and the clip position of the needle. The needle is held in position by a circlip type clip at the top of the needle. The needle has several grooves around it that the clip can be placed in. Selecting a high clip position puts the needle lower in the main jet and makes it leaner. Selecting a low clip position moves the need up higher in the main jet and makes it richer. Remember the needle is tapered so moving it higher puts a thinner, less blocking part of the needle in the main jet. Moving the clip is the normal way to jet the midrange but needles with different tapers or shapes are available.

Both the pilot jet and the main jet hang down into the fuel in the bowl of the carburetor. Vacuum draws the fuel up through the jets into the bore of the carb. For the pilot circuit, this vacuum is the manifold vacuum due to the engine sucking against a closed (or mostly closed) slide. For the main circuit (main jet and needle), the vacuum is venturi effect caused by the pressure drop of the air as it flows through the narrowest part of the intake tract. The more air that flows, the stronger the vacuum.

Since the fuel has to be sucked up from the level of the fuel in the bowl to the bore of the carb, the lower the fuel level in the bowl the less that flows for any given vacuum so low level leans the mixture. A high level richens the mixture. The fuel level in the bowl is controlled by bending the tab on the float.

There are two air jets, a pilot air jet and a main air jet. They supply emulsifying air for the pilot and main circuits. This sounds odd but a pure liquid stream of gas is hard to control because of surface tension, capillary action, and inertia. By mixing just a tiny amount of air, just enough that if you could see the fuel flowing in the jet, it would be maybe 1/8" of fuel, 1/8" of air, 1/8" of fuel etc. Like the flow through a straw as you suck up the last of a milkshake. The amount of air is neglible (1/2 by volume, maybe 1/100th by weight) so the air doesn't directly affect the mixture but it changes the weight of the stream delivered through the jet which affects the speed it comes out and the portion of air to gas that comes out. Again, this is just to make the fuel stream easier to control. Although it is useful for jetting, it was added to make the carb more predictable.

There are three other circuits. The choke circuit is another jet that drops down into the fuel and is only operational when the choke is out. Richens for starting and cold. The hot start circuit just dilutes the mixture with additional air (pirate air for you auto techs) to lean it when hot starting. And the accelerator pump to enrich on accelleration. The accelerator pump is literally a little diaphram single stroke pump bolted onto the base of the carb that pumps gas into the carb when the throttle is opening. One the throttle stops turning, the pump stops pumping. The pump is designed so it can pump enough for any application and is then limited for the exact application by letting part of the pumped gas leak back into the bowl instead of all of it going into the carb bore. This is controlled by the leak jet. A bigger leak jet will reduce the accellerator pump volume and a smaller one will increase it. A fuel pump is required on a non CV carbs because the vacuum falls rapidly as the open slide lets in a rush of air to fill the manifold and then stagnates briefly until the engine starts rev'ing to pull in more.

Hope that answered your question about the pilot and leak jet. Several years ago I wrote some long posts in the YZ250F/WR250F side called Jetting 101 and Accellerator Pump 101 that may still be there. I thought I was smarter then than I do now, so if someone can clarify or correct this, please do.

Mark Cantrell

p.s., just bought a 2005 CRF250 to replace an aging 2001 WR250F that is now for sale.

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Hi,

this is a re post of what I posted in the regular 250x group.

Last weekend I rejetted my 250x. I replaced the main jet, pilot jet and raised the needle clip.

First I raised the needle jet one clip. First I removed the tank / seat. Then I loosened the 2 clamps on the carb boots. I loosened 2 zip ties that hold some of the hoses / cables to the carb. Then I removed 2 metric hex bolts from the top of the carb. I had to rotate the carb to get the bolts out. Then I used the needle tool that was given with the bike and removed the needle. You might have to open up the throttle to raise the needle some to access it and remove it. Then move the clip to the position you want. Then just put the carb back together in the reverse direction.

Now the hard part. I removed the bowl drain cap on the bottom of the carb. Then I had to rotate the carb as much as I could and that was still a few degrees shy to fully access the lower needles. I used an 8mm socket and removed the main jet. This made getting to the pilot jet a bit easier. To access / remove the pilot jet you need a small / short screwdriver. The jet sits up inside "U" shape portion of the carb. This is why you need a small size screwdriver. Then the distance between the engine case and carb is very tight and that is why you need a short screwdriver. I ended up making a custom screwdriver out of an 8in craftsman screwdriver by cutting it down and re grinding a new blade. I also had to cut the handle down. The over all length was about 2in long then. Finally I was able to remove the pilot jet and replace it. Then I re installed the new main jet.

Then just re install the carb bowl cap and put the bike together in the opposite order. Don’t forget to tighten up the carb boot clamps. I wasn't able to come up with the 55 leak jet so I didn't need to remove the bowl off the carb. If you do then also change out the 5 bolts to metric socket bolts for easier access later.

I installed a 42 pilot jet and a 140 main jet and raised the needle clip one position to the 3rd clip from the top.

That is it. I took it out for a brief ride and all seemed good. The bike idled better that’s for sure and even sounded a bit better.

Doug

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I replaced my slow and main jets last night. I know this is tough without pix, but here it goes.

helibuf is right, it's best to remove the main jet to ease access to the slow jet even if you're not changing main jets. First, I loosened the clamp bands and rotated the carb as stated above. For the main jet, I used a 6mm shallow socket. I could just fit the socket into the bowl and a get a 6" ratchet onto the socket. In my case, both the main jet and the needle jet came out. Putting the needle jet back in was quite fun because the needle tip drops out of the hole into which the needle jet inserts. At first, I didn't know this and could not get the needle jet back into the carb while operating by feel. Finally, I inspected and saw that the needle was protruding out of the needle jet hole. I had to position a mechanics mirror under the carb bowl so that I could see that the needle jet was engaging the needle to install it.

For the slow jet, I used a flat blade driver bit for a drill driver. The bit is approximately 1" long and has a 1/4" hex shaft. I mounted it in a shallow 1/4" drive 1/4" socket. I could then sneak it up into the bowl opening, put on the 6" ratchet and get the slow jet out. Installing the new slow jet went pretty smoothly.

I'm at 5,300 ft elevation and the only changes I made were to change my slow jet to a 42 and the main jet to a 145. The bike is completely stock other than jets. It seems that I got max idle RPM at about 2.0 - 2.25 turns out on the pilot screw with these jets. The stock 40 slow jet required 3.0 + turns out for max idle. BTW, even at this altitude, the 145 main jet did not seem to be rich at all. Currently, it seems that the mixture may be a bit rich just off idle, so I plan to raise the needle clip one slot to lean it out a bit. Will post results.

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How 'bout R settings for Throttlejockey and I? I'm at 5k - 6,400' and burping and farting (so's my bike) with a bright blue pipe. (maybe that's Ti) - w/ a 165, stkpilot, 2nd leanest, out 2 from dealer.

I'm really hoping not to break this down 8 times to get balls on like I did on the orange one. I do know altitude is finicky. those 41mm FCR's have their own personality. If anyone's figured out this 250R, I would really appreciate a post.

Thanks - JD

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The engine on my bike is 100% stock. I only have about 50 hours on it. It ran great at first, but lately it has developed a serious low end bog. Before I mess with the jetting, I think I have to figure out what changed. If it ran great at first, but now has a bog at low end what do you think changed? I don't think it's a jetting issue if it ran great at first.

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Interesting you have a bright blue pipe. I have a dull near black pipe on mine. But again, I am running the JD Jet kit, a Bill's pipe exhaust and header and no backfire screen.

'04 CRF250R, Florida 0' elevation

Stock pilot, blue needle 2nd clip and 172 main. I'm not sure if I'm optimally jetted tho as I still have a bog at bottom (easily corrected with higher idle and some clutching).

But then again, it has always been my knowledge that if yer pipe is black, yer rich, if it's blue, yer lean.

I could be wrong!!! :cry:

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The blue needle is for cold temp!You should be using the red in the #5 from top and 172 with cage or 180 with out :cry:

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