CRF100F Lack of jetting information, part numbers!?
Posted 21 March 2012 - 09:13 AM
Posted 21 March 2012 - 10:43 AM
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
Posted 21 March 2012 - 11:07 AM
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
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
Posted 09 April 2012 - 06:54 PM
Posted 11 April 2012 - 02:03 PM
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
Posted 12 April 2012 - 04:25 AM
Posted 12 April 2012 - 06:51 AM
Posted 12 April 2012 - 09:58 AM
Posted 15 April 2012 - 07:58 AM
Posted 27 April 2012 - 09:44 PM
Posted 28 April 2012 - 08:27 AM
Posted 29 April 2012 - 08:54 AM
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.
Edited by CR125Honda, 29 April 2012 - 08:57 AM.