OK it took some pretty detailed searching to find any bit of information leading me to actual part numbers for my little PD series carb on my CRF100F. I finally found out JetsRus had a 38 and 40 slow jet, and 102, 105 main jets.... So I ordered them, I took off my little CRF carb and noticed the stock slow jet was a "35s" whereas the new jets I just ordered were not "s" designated with the smaller hole design for better atomization.... Does anyone know where to get these specific jets like a "38s" or "40s"? Id much prefer these over the standard larger hole design... I also found part number 99103-KA9-0380 which is a honda OEM #38 slow jet... However, I do not know if this is a "38s"? as of right now I might just drop in the standard 38 jet I have... My bike wont start under full choke at all. when I open the choke up just a hair it will light up but not idle until I keep the throttle at 1/4 twist or so. after the bike is warmed up It will idle fine without any choke. I also had to play with the fuel screw a little to get it to idle like this after warm.
CRF100F Lack of jetting information, part numbers!?
Started by
treysoucie
, Mar 21 2012 09:13 AM
16 replies to this topic
Posted 21 March 2012 - 10:43 AM
You have a picture of the slow jet with the size and the letter S next to it?
I've never heard of any Keihin Jets being designated differently, you might be confusing the Keihin logo that is stamped next to the jet size, it looks like this:
I've never heard of any Keihin Jets being designated differently, you might be confusing the Keihin logo that is stamped next to the jet size, it looks like this:
Posted 21 March 2012 - 10:51 AM
If you look at the top left of this picture you will see the "35s" this is the slow jet my crf100f has in it.
Posted 21 March 2012 - 11:07 AM
Taken from: http://www.xr650r.us/jetting/
Quote
One of the most common questions asked on the subject of jetting is "What's the difference between a 68s and a 68 pilot?".
Only a little, but it makes a big difference in fuel flow! Below are two pictures of pilot jets. The top is a normal 68, while the bottom is of a 68s. Notice that the 68s has smaller emulsification holes. Though hard to see in the pics, the "s" has an "S" in the stamped markings.
Here's what Gary thinks of the different jets:
The 68 pilot jet is similar to the 68s. They both share the same main orifice size for the discharge nozzle, but the 68s has smaller emulsion holes on the sides of its tube as you can see by the picture. The smaller holes on the 68s pilot jet reduces the amount of air that mixes with the fuel before the emulsified mixture is discharged through the jet's nozzle.
Now for a bit of Haymakers free trivia: Websters defines "emulsification" as "To make into an emulsion", where the definition of such is the following:
A suspension of small globules of one liquid in a second liquid with which the first will not mix: an emulsion of oil in vinegar.
Now substitute "oil in vinegar" for "fuel in air", and there you have it!
"What does all this mean?" You ask? The size of globules into which the fuel is made by the jet drastically changes the rate in which it will burn. A Charge of air and fuel will burn much faster and with more force when there are more, though much smaller, droplets of fuel involved. I believe that the different jet has a direct correlation to the fact that the big XR is epa certified for emissions. Maybe I can get Gary to provide a little more insight as to why this change has been made.
Here's a bit of real world theory to help you understand how fuel burns. If you were to light a cup containing gasoline, only the surface of the cup would burn. You'd get a orange, smokey, flame, meaning that it was not burning efficiently.
If you were to take that same cup of fuel, atomize it into a fine mist in an enclosed space with the proper 15:1 ratio of air, then light it, you'd see the difference small globules make. Something I once read stated that "1 cup of gasoline will lift 1 ton, 100 feet, in one second." Maybe it's not correct, but it's something to think about as you are trying to put out your eyebrows because you had to check and see if I know what I'm talking about.
Well, that's about all I have for now. If anyone has any constructive criticism or recommendations, please let me know.
Only a little, but it makes a big difference in fuel flow! Below are two pictures of pilot jets. The top is a normal 68, while the bottom is of a 68s. Notice that the 68s has smaller emulsification holes. Though hard to see in the pics, the "s" has an "S" in the stamped markings.
Here's what Gary thinks of the different jets:
The 68 pilot jet is similar to the 68s. They both share the same main orifice size for the discharge nozzle, but the 68s has smaller emulsion holes on the sides of its tube as you can see by the picture. The smaller holes on the 68s pilot jet reduces the amount of air that mixes with the fuel before the emulsified mixture is discharged through the jet's nozzle.
Now for a bit of Haymakers free trivia: Websters defines "emulsification" as "To make into an emulsion", where the definition of such is the following:
A suspension of small globules of one liquid in a second liquid with which the first will not mix: an emulsion of oil in vinegar.
Now substitute "oil in vinegar" for "fuel in air", and there you have it!
"What does all this mean?" You ask? The size of globules into which the fuel is made by the jet drastically changes the rate in which it will burn. A Charge of air and fuel will burn much faster and with more force when there are more, though much smaller, droplets of fuel involved. I believe that the different jet has a direct correlation to the fact that the big XR is epa certified for emissions. Maybe I can get Gary to provide a little more insight as to why this change has been made.
Here's a bit of real world theory to help you understand how fuel burns. If you were to light a cup containing gasoline, only the surface of the cup would burn. You'd get a orange, smokey, flame, meaning that it was not burning efficiently.
If you were to take that same cup of fuel, atomize it into a fine mist in an enclosed space with the proper 15:1 ratio of air, then light it, you'd see the difference small globules make. Something I once read stated that "1 cup of gasoline will lift 1 ton, 100 feet, in one second." Maybe it's not correct, but it's something to think about as you are trying to put out your eyebrows because you had to check and see if I know what I'm talking about.
Well, that's about all I have for now. If anyone has any constructive criticism or recommendations, please let me know.
Posted 21 March 2012 - 12:48 PM
Well, I have a couple of XR100 carbs here, and there is no S on the pilot jets, and I hardly think that there would be a noticable difference between the two in a 20mm carb. It might be a little more noticable in a Keihin carb on a much bigger bike, but I think you'd be able to pop the regular #38 pilot jet in your carb, and, once dialed in, run like a champ. I say try it and see what happens.
It looks like someone try to use the Vise-Grip straightslot screwdriver on the other jet in the pic, what happened there?
Keep us posted on your findings with the regular pilot jet...
It looks like someone try to use the Vise-Grip straightslot screwdriver on the other jet in the pic, what happened there?
Keep us posted on your findings with the regular pilot jet...
Posted 21 March 2012 - 12:57 PM
That pilot jet pic was searched through google, but it is what my 35s looks like. Since its not my actual pic, I couldnt say what happened to that jet... If the oem #38 jet I ordered is just a standard #38 without the smaller holes then i'll just stick it in there... It will be better than the 35s I have now, as it does not idle properly with my uncorking mods and FMF exhaust
Posted 09 April 2012 - 06:54 PM
Well I have the same problem. With the 38 I still cannot start on full choke. I still merchant to open it a hair in order to start. The low end seems a little worse now and so does midrange. and quick action throttle response. The top end seems better though. What should I try next?
Posted 11 April 2012 - 02:03 PM
Adjustment of the needle (via the clip/notches at top of needle) made a significant difference to starting on my XR100 (120 BBK, full exhaust and Uni pod filter).
Also note valve lash adjustment should be checked prior to making carburetor adjustments. FSM says to set the gap to .002", I like them loose at .003".
Also note valve lash adjustment should be checked prior to making carburetor adjustments. FSM says to set the gap to .002", I like them loose at .003".
Edited by theraymondguy, 11 April 2012 - 02:08 PM.
Posted 11 April 2012 - 03:16 PM
Yes I will check valves any this weekend and see If any changes. There's a few guys who race motarded minis here in Houston that are running 40 pilot and 105 main with just airbox mods and exhaust. I don't have fuel screw or jet needle adjustment on this bike. The jet needle has only 1 clip position.
Posted 12 April 2012 - 04:25 AM
There's a couple of things that don't seem to sound right here. I looked up the OEM part number for an '06 CRF100 pilot jet, the number was 99104-KN4-0350. That jet was used on the '01-'03 XR100R and the '04-'12 CRF100F. The 99103-KA9-0380 pilot jet was used on the '82-'85 XL100S and the '82-'00 XR100R. It almost sounds like you don't have the original carb that came with the bike, especially having a jet needle with only one notch. The '05 or '06 CRF50F and newer carbs only have one notch on the jet needle, but wouldn't be interchangable with the much bigger 100 carb.
Posted 12 April 2012 - 06:51 AM
I will need to verify tonight if the jet needle is or isnt adjustable. I was going off information I had read on another forum. I did not actually look at the jet needle myself for adjustability. With that said, I know my fuel screw is a "D" shaped screw that needs a special tool to adjust. Does anyone know the part number I can use from the 05 and older CRF that will replace my D shaped fuel screw and make it adjustable? I think the stock number for an 08 "D" shaped screw is: 16016-KSJ-A01 and part number for the adjustable screw on an 05 is: 16016-KN4-L10? Am I correct?
Posted 12 April 2012 - 09:58 AM
Yes, the 16016-KN4-L10 is the screw set A that was used on the '98-'03 XR100R and the '04-'05 CRF100F.
Posted 15 April 2012 - 07:58 AM
Hope this helps. After finding my pilot jet had fallen into float bowl it was so clogged decided to get a new one. Yes the one in it was indeed a 35s and dude at parts counter had never seen one w/s after #. Sold me a regular #35 and bike seems to run fine with it installed.
Posted 27 April 2012 - 09:44 PM
Based on all the info I've found this is the stock 08 Carb. They also come with non adjustable jet needles. Does anyone know the part number for a jet needle( maybe an 05) that has adjustable clip positions.
Posted 28 April 2012 - 08:27 AM
I looked it up and found different part numbers between the 05 and 08. But it didn't tell me If the older model part was the adjustable one
Posted 29 April 2012 - 08:54 AM
Just went throught the same type of issue with a 2002 XR 100.
My 35 "S" pilot/slow jet was clogged. Soaked it in cleaner but the clog was still there.
Used a very small dril to open it up and didn't realize how small the opening down inside realy was. My drill bit was too big.
Not thinking about if there was a difference between a 35 and 35S, I ordered a 35 jet off eBay.
The difference between the two is the size of the emulsication holes (four ea. on the top side of the jet).
They are smaller in size on the 35S jet. Enough to notice visually.
From what I read, the size of the holes make a significant difference in how the fuel is atomized.
The bike runs pretty good at idle (and idle to 1/4 throttle transistion) with the 35 jet in it but I think it could probably be finely tuned just a little bit better with the 35S.
I'll order one next time I need some other parts.
Ken
My 35 "S" pilot/slow jet was clogged. Soaked it in cleaner but the clog was still there.
Used a very small dril to open it up and didn't realize how small the opening down inside realy was. My drill bit was too big.
Not thinking about if there was a difference between a 35 and 35S, I ordered a 35 jet off eBay.
The difference between the two is the size of the emulsication holes (four ea. on the top side of the jet).
They are smaller in size on the 35S jet. Enough to notice visually.
From what I read, the size of the holes make a significant difference in how the fuel is atomized.
The bike runs pretty good at idle (and idle to 1/4 throttle transistion) with the 35 jet in it but I think it could probably be finely tuned just a little bit better with the 35S.
I'll order one next time I need some other parts.
Ken
Edited by CR125Honda, 29 April 2012 - 08:57 AM.
