The bike will run with no main jet until about 5/8-3/4 throttle (which you mark on the throttle with masking tape and a pen) and it will then fall on its face with a too rich condition. This is good because you now know what a rich main jet feels like as opposed to a lean condition. Until this position the needle jet and the jet needle are the restrictions to flow with the pilot circuit also adding to the mix. The important thing is you don't want the main jet to restrict fuel until the jet needle and needle jet are no longer a dominant factor (restriction). If your main was too small then it could restrict fuel flow before the jet needle and needle jet do so, so in fact your 1/4-3/4 range which is primarily controlled by these jets could actually still be too rich but the too small main jet is giving you a false impression and the main circuit will also be too lean. Fuel flows through the main jet before the needle circuit.
After you have set your pilot jet size first (because the pilot will also contribute fuel through out the range and is separate and additional to the other circuits, if you've ever had a blocked one you will realize this) and the air screw and you know that your needle jet and jet needle are correct with good engine response and no lags, bogging, coughing or pinging (you should not need to worry about the needle jet which is the jet the needle moves inside, they seldom need changing) and you know what a rich main feels like you can then fit a main that you expect is close but probably too rich and ride the bike. Then keep coming down one size at a time until you clear up the rich main jet symptoms. I like to find the main that is still too rich then come down one size from there.
Once the main circuit has been sorted with the other circuits you might need to fine tune the air screw.
You can now be confident on full throttle runs down 2km straight a ways (and I've seen seized bikes on these) and hard uphill climbs in the sand or what have you that your bike is not lean and going to seize or do damage.
A bike that is too lean will sound loud crisp and raspy and possibly ping or idle high on coming to a stop.
Over seas recommended jetting specs don't always apply with our different fuel and humidity at sea level etc.
Can't help you with that needle sorry Reckless.
Twice the displacement, twice the cost and a decibel problem, I'll pass on the inside brraaaap!!!
yep the way I see it in describing his tuning method Danger explains pretty much how a 2smoke carb works! We actually spend most of the time when enduro riding on the Needle and the needle jet (or Emulsion tube).
His method of leaving the main out to eliminate any interference or influence from that is a good idea.
He's quite correct the main doesn't have any effect until the needle lifts out of the emulsion tube high enough to get to the point the area that's left is larger than the area of the main. Unless the main is to small as he describes.
Major rule of tuning! If in doubt or got a flat spot or miss "always go rich first". no ones ever lunched an engine from being to rich!
Anyway if anyone is following this thread I've scanned the diagram from the Ktm manual on where each jet comes into the throttle position. If you read Dangers post in conjunction with this, it all becomes obvious!
On a Motorcycle you're penetrating distance, right along with the machine!! In a car you're just a spectator, the windshields like a TV!!
'Life's Journey is not to arrive at the grave safely in a well preserved body, but rather to skid in sideways, totally worn out! Shouting, ' Holy sh!t... What a Ride!! '
I can only add that I spend most of my time jetting for idle to 1/2 throttle ,,in fact I remember once forgetting to put the main jet in ,,,and didnt notice until I came in and made a jetting change ,,..
A cheap and cheerful data logger is the missus camcorder. taped to the bars recording the throttle ( I have a degree disk that slips over the bars , but tape and a pen work just as well.
You might be surprised how much throttle you use ....
I have got to do the same thing right now ,,,but its cold and gloomy out there today ,,,and I am making cheap excuses ,,,,,,,hense the length of this email
Stephen
"Look, Madame, where we live, look how we live ... look at the life we have...The Republic has forgotten us."
Thanks Reckless and tommorth, but I need to be careful about over-thinking this whole thing! There are some charts etc. on KTMtalk about needle numbers and tapers, but I only skimmed it all. Too much for my feeble brain at least for the moment and too many options can lead to trouble. I should be OK trying a few different combinations out inside a limited range.
Looking at my handbook chart, that NOZE needle seems like it will be a fair bit too rich for my carb so possibly not worth troubling you for it for the time being, thanks though.
I'll have another read/ponder then email JD. I do find it a bit strange the JD needles don't have any numbers, does make it hard to compare. Even the colours seem back to front to me! Next change, I'll measure both needles top to bottom like I should have done to begin with. Next time I'm in shop, I'll grab an NZOF and buy or measure it, then I'll have some sort of baseline to go off.
Pity we can't ride on the beach anymore. Seems like a decent place for a jetting session. No bumps, corners or tree roots etc. Quite keen to try this wet line jetting, seems like a good way of avoiding being lean somewhere and not being able to pick it up riding.
:::::::::
Thanks danger. Been trying to get a better grasp of the way the different circuits overlap/interact. I did like the principle of this 'no main' when I first read it, seems an excellent idea to be able to isolate each aspect a bit more.
Sorry - more questions:
Just to confirm my understanding - the main ONLY comes into effect (unless main too small) at the higher throttle positions, no affect at all below this? Seems like my idea of main/needle relationship might have been way off.
Is the needle jet the part that is permanently staked into carb body where main jet screws into (from memory)? Carb parts diagram I just looked at doesn't show all. Edit: Whoa. info coming thick and fast. I've looked at that diag in handbook before and didn't really believe it. Now looking for carb cross-section pic to compare.
Is the needle jet the part that is permanently staked into carb body where main jet screws into (from memory)? Carb parts diagram I just looked at doesn't show all. Edit: Whoa. info coming thick and fast. I've looked at that diag in handbook before and didn't really believe it. Now looking for carb cross-section pic to compare.
yes this is the Emulsion tube or some call it Needle jet. It is usually brass and is screwed down into the body of the carb. They can be changed but highly unlikely you'd need to if yours is standard. Yes the main screws into it.
Originally Posted by camchain
Just to confirm my understanding - the main ONLY comes into effect (unless main too small) at the higher throttle positions, no affect at all below this? Seems like my idea of main/needle relationship might have been way off. .
Very hard to explain in writing but think about the hole between the needle and emulsion. Or the m2 area that's left at any throttle position between the taper and tube. As the needle rises this increases this gap/area letting more fuel in, So its a simple matter of measuring this gap.
So until this gap gets bigger than the area of the main it demands less fuel than the main delivers, therefore the main is only used as a hose feed and has no effect. I've drawn over the Drawing to help explain. Pretty primitive but I've tried to draw it as the jets relate to the power delivery. Its not till YY area gets bigger than XX area that the main has any effect. Simple process of area comparison or flow volume.
People get confused by the fact that except for the pilot/idle jet circuit all the fuel comes in via the main but its the measuring or metering effect of the needle in the tube that actually controls how much fuel is delivered to 3/4 throttle.
HAHA now we can talk about Power jets LOL!! Basically a tube from the bowl directly into the back of the carb!!
Shit now I gotta work late cause of bloody KB again!! I like these topics though! LOL!!
On a Motorcycle you're penetrating distance, right along with the machine!! In a car you're just a spectator, the windshields like a TV!!
'Life's Journey is not to arrive at the grave safely in a well preserved body, but rather to skid in sideways, totally worn out! Shouting, ' Holy sh!t... What a Ride!! '
Man I find Jetting really confusing. I want to have a bit more of a play with mine, but scared of fucking it all up. Interesting reading here though guys. My bikes jetting is completely stock and I think that it should be altered cause of the aftermarket pipe.
Where do you think the best place to jet your bike would be? I'd be scared of doing it at woodhill cause too many meatheads ripping it up in the pits. Would thunder be an ideal place?
Uh-Oh. I've managed to turn this into a "*how does my carb work?" thread. Sorry.
i need to go back and read notes thoroughly. Some of the stuff I just read again about main jet is conflicting. Found this carb cross section pic. It's a CV carb but it shows the basics. Will delete if someone finds a more useful pic.
Edit: Ha. Posted almost at same moment Reckless. I haven't done any work at all today. I like what you did with that diagram - very clever. No bloody wonder I didn't notice any difference when I was trying to 'feel' a main jet change at around half throttle. 'Someone' (?) should run a jetting clinic day on a lonely beach somewhere?
Last edited by camchain; 24th February 2009 at 19:29.
Reason: * edit - bad first description
Good diags Danger small point that your first one shows. There is some overlap or transition between all fazes. I like the GIF. Just need to work out how to slow it down.
I think we've done as much as we can on a forum.
Danger all the above doesn't really explain why we would change needles.
Given the bikes running OK a NOZE or NOZF might feel the same or very similar. I'd try a change it because the plug looked wet/dark or dry/light.
Do you do it entirely by feel?
On a Motorcycle you're penetrating distance, right along with the machine!! In a car you're just a spectator, the windshields like a TV!!
'Life's Journey is not to arrive at the grave safely in a well preserved body, but rather to skid in sideways, totally worn out! Shouting, ' Holy sh!t... What a Ride!! '
That needle is what comes in the bike when retricted to meet the ADR Regs so is an extremely lean needle. It should have been taken out and replaced with the NOZF 4th Clip with 162 main for 2007 200EXC.
Just a point re following the KTMTalk re jetting specs in that the fuel we have here in Godzone has a slightly lighter Specific Gravity meaning we do need to runslighty different jet settings.
On dyno runs and the six days in Taupo we came up with the following rule of thumb when looking at the jetting charts supplied by KTM. Älways use the next warmer temperature range jet specs to that of the actual current temperature range. This implies you will actually be running approx 5% leaner across the board. We have had zero problems when applying this to KTM and the bikes run well.
Hope this helps team. Give me a ring on 09 265 2135 if you want to discuss jetting for specific riding conditions as we do not have enough space in this forum to cater for everyone.
Also do not be afraid to play with the powervalve preload adjuster but make sure you know where you started and that point is always "Dimension Z" inthe spec sheet. Adjustment makes the bike a lot more rideable in the wet stuff. Cheers
The NOZE & F needles I was talking about where in reference to my sons 03 bike I have. Came with the E and I changed it to the F.
Never had the R1475J in, and I wouldn't have tried as it looked far to big in the taper diameter and above. What you say makes complete sense thanks for that, now at least I know what it relates to, cheers.
My 08 has a 42 Idle, NOZH, 4th clip, 165 Main, 40:1. But I moved it to clip 3 to lean it a bit because I'm probably riding it lower in the revs than the guy that used to race it before. And it was a bit boggy down low. That made a big improvement to it, but I reckon there's more to be done there!
If anything the bike still seems a bit rich even though my needle is two steps leaner than you suggest for the 07?
Is the 42 a bit large, book says 42? Air screw is about 1-5-1-3/4 turns so that says the Idle jet is close.
Can we really compare it to the 07 because they completely revised the crank case flows, transfers, carb etc between those years didn't they?
Also I'm used to the 03 I had which kicks like a mule down low, but I don't want to make this bike like that, the 08 is much easier to ride and it climbs much better!
I'm pretty sure I could clean up the low/mid heaps (maybe try a straight taper set up) but it goes better than I can ride it so have left it alone till I get the suspension done. Also need a new side stand but want a stepped seat (heard they are really really good for body position on the bike), new tyre, sump guard, Radiator Guards, steering damper, ride 100 hrs this year! shit it never ends and my money tree has no leaves?
PS Steve do you have those better aftermarket side stands in stock!
On a Motorcycle you're penetrating distance, right along with the machine!! In a car you're just a spectator, the windshields like a TV!!
'Life's Journey is not to arrive at the grave safely in a well preserved body, but rather to skid in sideways, totally worn out! Shouting, ' Holy sh!t... What a Ride!! '
Hmm. More useful info above. Seems like there is a bit more margin to sneak up to a leaner setup. Interesting quite a different needle in your 08 reckless. Thanks for the reminder on the diesel fuel screw/2 banger air screw danger. Back to the notes again, maybe I'll do some work tomorrow. I have a couple of different carb system diagrams saved now and they often show slightly different - but overall a much better mental picture is forming. Feels good to have my ignorance level reducing.
Kind of surprised now, that subtle changes in needles have so much affect. guess I'll soon be making some 0.05mm shim washers to raise needle for when sun goes behind a cloud. Cheese is right, where's the best place to do this stuff?
OK, sorry but here's another carb question that's always bugged me: Many years ago a mate seized his PE400 coasting down a long steep hill with the throttle off. Ever since I've been a bit paranoid and I give the throttle a few blips when in this situation. Guessing there's a similar risk when running wide open then suddenly shutting off gas.
I know the little holes on engine side of carb throat (one hole being idle) are supposed to take care of this by delivering a bit of fuel when throttle closed but how well does carb really handle closed throttle, but higher engine speed?
No need for stepped seat reckless - I find my standard seat is OK as long as I keep my arse off it. (Legs don't always agree with arse though, so I try to ignore them both)
short answer when you close the throttle at high revs the pilot jet may not supply enough fuel/oil which not only lubes the crank but cools the piston piston gets hot because not enough fuel to cool it and expands lean condition also causes bike to run hotter and detonate this can cause bike to seize
"The world is a strange sad place. Ride as often as possible and try not to think about it".
Simply pull in the clutch??
Honestly this situation wouldn't often arise!
High revs using the engine compression only to slow down, no blips between gear changes, no periods when you pull the clutch in to get around an obstacle and give it a blip to keep it going?? The thing must have been pretty lean for there not to be enough residue on the barrel walls as well.
Even when we do a plug chops we pull in the clutch.
Wouldn't sweat about it Cham alot of time has gone past since the PE400 days, probably even a cast iron bore, was it even water cooled??
You'll go crazy being that paranoid. If your worried pull the clutch and use those great Brembo's we've got!!
I am gonna try a stepped seat. If my mate who's been riding for many years, and is very good, really likes the one he's just got. I'm gonna give it a go! He liked it because it forced him to sit in the correct position every-time. I'm always sitting to far back, so sounds like just what I need. Lower seat might help when your stuck on a slope as well. Quite like the thought of sitting, in it, not on it, as well. Won't know till the money tree grows some leaves! Gonna spend it with Danger first hopefully he'll do me a good deal!
On a Motorcycle you're penetrating distance, right along with the machine!! In a car you're just a spectator, the windshields like a TV!!
'Life's Journey is not to arrive at the grave safely in a well preserved body, but rather to skid in sideways, totally worn out! Shouting, ' Holy sh!t... What a Ride!! '
Simply pull in the clutch??
Honestly this situation wouldn't often arise!
High revs using the engine compression only to slow down, no blips between gear changes, no periods when you pull the clutch in to get around an obstacle and give it a blip to keep it going??
Top of the south is very steep and can have downhills that take minutes to get down (or at least seems like it???). So the question perhaps is, how long is a "long" downhill that would cause a problem?
In this situation I give the engine a rev (usually clutch disengaged) every 15 secs or so.
Cheers,
Colin
Originally Posted by Steve McQueen
All racers I know aren't in it for the money. They race because it's something inside of them... They're not courting death. They're courting being alive.
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Originally Posted by camchain
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