Mark Krieger saved my KLX
#11
07-12-2011, 03:09 PM
Join Date: Mar 2010
Location: South Puget Sound, WA
Posts: 740
Pilot or idle jet system. The idle jet controls the idle and on up to quarter throttle, give or take a bit. On some carbs, like Mikuni there is an air jet too. In conjunction with the idle jet there is an idle jet air screw. This screw leans or richens the fuel mixture for a smooth idle and on up to one quarter throttle. From the idle jet, there are little passages cast into the carb that lead to holes just in front of the throttle valve or plate. There can be just one hole or there can be several, depending on the carb design. They effect the mixture as long as the vacuum, in the venturi, is over them. As the throttle opens further, the vacuum moves to the needle jet and jet needle.
The Throttle Valve. The big slide that opens and closes your throttle has a bevel angle cut in one side of the big round (can be flat, too) slide, toward the air cleaner. This angle comes in several sizes and helps control the fuel mixture from idle to about 35% open throttle.
Needle Jet. This jet doesn't really even look like a jet, but it is ! It controls the fuel mixture from 15% to 60% open throttle. It sets in the center of the carb, right over the main jet.
Jet Needle. This is the needle that rides in the throttle slide and goes into the needle jet. This needle controls the fuel mixture from 20% to 80% open throttle. It can come in many different sized tapers. Sometimes, one needle can have several tapers on it. The top end of the needle has grooves cut in it, usually five, and you can move the little clip on the end up or down to lean (down) or richen (up) the mixture. Most late model bikes have needles with only one groove cut in them. This is so you can't richen the mixture, thereby keeping the EPA happy.
Main Jet. This jet controls the fuel mixture from 60% to 100% open throttle.
I'll stick to pilot jet...
The Throttle Valve. The big slide that opens and closes your throttle has a bevel angle cut in one side of the big round (can be flat, too) slide, toward the air cleaner. This angle comes in several sizes and helps control the fuel mixture from idle to about 35% open throttle.
Needle Jet. This jet doesn't really even look like a jet, but it is ! It controls the fuel mixture from 15% to 60% open throttle. It sets in the center of the carb, right over the main jet.
Jet Needle. This is the needle that rides in the throttle slide and goes into the needle jet. This needle controls the fuel mixture from 20% to 80% open throttle. It can come in many different sized tapers. Sometimes, one needle can have several tapers on it. The top end of the needle has grooves cut in it, usually five, and you can move the little clip on the end up or down to lean (down) or richen (up) the mixture. Most late model bikes have needles with only one groove cut in them. This is so you can't richen the mixture, thereby keeping the EPA happy.
Main Jet. This jet controls the fuel mixture from 60% to 100% open throttle.
I'll stick to pilot jet...
Your pilot jet is already a #35 from the factory and way way bigger than 18 thousandths. Your cut and paste of carb circuits shows us nothing.
#12
07-12-2011, 04:32 PM
So a jet drilled to .018" (#77) or .4572 would be significantly larger than a #35 pilot at .35mm diameter or .014" in the world of pilot jets.
I hope this helps a bit.
Last edited by klx678; 07-12-2011 at 04:44 PM.
#14
07-12-2011, 06:12 PM
Join Date: Mar 2010
Location: South Puget Sound, WA
Posts: 740
So if I do the math, a 0.018" hole is touch bigger than a #45 mikuni jet. Pretty amazing that the OEM #35 pilot is less than 0.014".
I bet a dollar that the OP drilled his choke jet using the super common procedure to 0.018" and just doesn't know what the to call the jet. I tried to nicely let him know and maybe he would fix his sig line.
I bet a dollar that the OP drilled his choke jet using the super common procedure to 0.018" and just doesn't know what the to call the jet. I tried to nicely let him know and maybe he would fix his sig line.
#15
07-12-2011, 07:18 PM
And I'll add a dollar to that considering the set of information he googled from the internets doesn't even match up to the circuits in our stock carbs. But then again the internets are NEVER wrong....
#16
07-12-2011, 07:22 PM
I remembered that Mikuni did something like that and in doing research found fact that the mains are labeled that way. The inch value is simple use of the 25.4 conversion (25.4mm=1") take the #35, make it .35/25.4=.013779. There's a karting site that has a listing of jet sizes with metric/english comparisons and there were a number of references to the labeling. Finally there was the table relating metric, number drill wire guage, and decimal equivalents. Became clear that what I remembered was still the same.
I will say something does seem amiss in the references. One good reason not to print them I guess.
I will say something does seem amiss in the references. One good reason not to print them I guess.
Last edited by klx678; 07-12-2011 at 07:33 PM.
#17
07-12-2011, 07:28 PM
My original information, that I based my comment on and backed it up with the internet sources, happened to be what I'd learned back in the mid 80s when doing jetting on one of the SR500s I had. Real printed information from reliable sources... imagine that!
I think I may have found it in an old Sudco or GEM catalog in their jetting information or one of the magazines, since they used to actually tell you how to do things back then rather than tell you where to take it and get it bolted on. Ah for the days of Gordon Jennings, Joe Minton, and far less litigation based on stupid actions by fools.
Last edited by klx678; 07-12-2011 at 07:42 PM.
#18
07-12-2011, 07:40 PM
Oh, they do make bigger. I was desparate for a bigger pilot jet once in the Bultaco Sherpa T. All I had was a 25 and an 80! I put in the 80 and adjusted the air screw (it was air on the early VM24 and yes tiny carb, but it's a trials bike). With that huge pilot the air screw was so far out I actually put a dab of silicone seal on it to hold it from coming all the way out. Bike finally idled, but not too good. Worked much better when I actually got I think either a 35 or 40 in it. Way better. But I was young and impatient, had to try what I had.
#19
07-12-2011, 09:03 PM
Before someone loses an eye here, I'll stand corrected. My cut and paste was me researching the term enrichening jet and coming up with nothing. I'm not a carburator expert and don't claim to be one. Yes, the jet I drilled was indeed the enrichening circuit jet (you learn something new every day right?). I am no idiot either, just not all up on carburator terminology. Peace.
#20
07-12-2011, 10:04 PM
If some of your post takes aim toward my post too, I'm not quite the fool you apparently may think I am.
My original information, that I based my comment on and backed it up with the internet sources, happened to be what I'd learned back in the mid 80s when doing jetting on one of the SR500s I had. Real printed information from reliable sources... imagine that!
I think I may have found it in an old Sudco or GEM catalog in their jetting information or one of the magazines, since they used to actually tell you how to do things back then rather than tell you where to take it and get it bolted on. Ah for the days of Gordon Jennings, Joe Minton, and far less litigation based on stupid actions by fools.
My original information, that I based my comment on and backed it up with the internet sources, happened to be what I'd learned back in the mid 80s when doing jetting on one of the SR500s I had. Real printed information from reliable sources... imagine that!
I think I may have found it in an old Sudco or GEM catalog in their jetting information or one of the magazines, since they used to actually tell you how to do things back then rather than tell you where to take it and get it bolted on. Ah for the days of Gordon Jennings, Joe Minton, and far less litigation based on stupid actions by fools.
Printed sources of information can and have been wrong too. As long as a human is involved, there'll be SNAFUs.
Another name for it, btw, is "starter jet".
Heh, and there I go quoting one person and talking to the other. That and my previous post were directed towards klxrida...
Last edited by WhiskeyTF; 07-12-2011 at 10:08 PM.