Not another jetting question... ok it is a jetting question [Archive]

View Full Version : Not another jetting question... ok it is a jetting question

cheese

30th June 2008, 20:52

So i Raised my needle to third clip down (it was 2nd clip down which is factory) and my bike rean really well through the bottom end once it was really hot and warmed up, but top end was slightly boggy and slow to come on. So I think that I made it richer? I'll put it back to normal as I won't have another chance to test it much before tarawera, but I think that I should have dropped teh needle down a click?? but then it will be at its max adjustment. Wasn't keen to start adjusting it at woodhill in teh rain.....

Reckless

30th June 2008, 23:24

Shit I wish I had come out with you on Sunday we would of had this sorted.
Yes you richened it, what you did was raise the needle so at full throttle the needle was further out of the hole in the main jet. Therefore passing more fuel through in the upper range. Which equals a blacker centre on your plug. It also moved the taper up a bit giving a bit more fuel low/mid range that is probably why it felt stronger at the bottom.That is exactly the effect of different tapers on diff needles. But sounds like it was giving a bit to much at the top of the range.
OK put it back to what you had, that's your benchmark as you know what the plug looks like ( I hope) in that position and how it goes. Now if you move it the other way to lean it, it will lean as much as it richened the last move, if you get what I mean. Don't worry about if the clip is in the last notch that just means next move of the needle down requires a main jet change and reset it back to the lower clips, it is no problem for a needle to be on the first or last clip position. So your decision is based on the colour of the plug in your std position. Will a move turn your plug a lighter brown or copper (depending on the oil you run), or will it make it white or to lean. Its a judgement call based on whipping the plug out and making an educated guess. If your not confident just go back to std, but if your plug is blackish when hot you probably can afford the move. If you don't know how your plug runs normally, leave it alone until you've had it out a few times and know how it runs.

PS Jetting a 2smoker is done on plug colour. You cannot do the fine tuning by feel alone. You must whip the plug out when its hot and read it and NOT when its idled all the way back to the pits.

Hope this helps Cheese!

cheese

1st July 2008, 09:05

Sure does. I'm feeling a bit more confident to have a play, but woodhill is not the place to do it I think. Too many meatheads ripping it up in teh pits and it was wet as hell + the rain. Think I'll have to take a trip out to Ardmore or maybe thunder would be better. I've got to get some spare plugs too todo teh jetting. The only other thing that I noticed is that I've got a FMF pipe and FMF say main jet should be 410 (I've got 420 which is factory) and everythign else leave as factory. I mihgt grad a jet of Scott adn play with it after T100.

Probably not a bad thing to run it rich on my fresh piston on rich jetting.

Reckless

1st July 2008, 10:25

Actually would think the Sandpit would be good for tuning but Ardmore or anywhere is OK. If your getting near the top clip position a jet change like the FMF guys say may be on the cards. BUT it doesn't hurt for us to run ours a bit richer with the sort of riding we do. As long as they are not smoking heaps and fowling plugs or so rich there is bore wash and the rings aren't bedding in that's not a bad thing at all. From what I remember yours is running OK its just fine tuning you want.
Also I tend to favour things a bit rich, it tends to give fat, strong power rather than lean which to me feels thin, revvy and brittle. For what we do fat is better. Different if your a flat out track based MX racer and your always smack in a certain rev range.

OH boy are we getting into some tech terms NOW!! LOL!!!

A thing to remember with a 2stroke generally what you give to a point in the power range you take from somewhere else!!

barty5

1st July 2008, 10:52

there is a good sized empty lot down bush road been there for years have used that in the past for tune ups only nice and close to home. Not that i recommend riding on building site as general partice.

B0000M

1st July 2008, 14:37

so on a 2smoker you look at the plug to determine your jetting, how do you do it easily on a 4 smoker? removing the plug is not an easy feat.

Reckless

1st July 2008, 16:43

On a 2smoker you read the plug to see how its running. You determine the jetting changes by experiance from there. Thats if you don't have EGT (exhaust gas temp) and CHT (cylinder head temp) readings and a few previous blow ups to give you a line in the sand like we did on our karts.

I know fuck all about 4 stroke plug reading and they don't have oil in their petrol to give so much colour information. So I guess a white plug means lean, grey plug not so bad and black plug to rich. Wether or not you can say the outer ring wetness or colour is generally low and the electrode colour mostly main jet as a guide, I don't know.
I would guess very light or white anything is far to lean. And the general tuning rule: Always try richer first would also apply.
Thats what cheese did in the weekend, which was good.

See this is what they want!! For the bike to have to go back into the shop everytime you have an issue!! Thats why they are dropping 2strokes, cause as a whole, 4 strokes generate much much more revenue!!!!!!!!!!!!!!!!!!!!

B0000M

1st July 2008, 17:32

4 strokes suck... see ive had one less than a week and i allready hate it

theblacksmith

1st July 2008, 18:20

There are HC and CO emission testers available. One of these would tell you exactly what your running on a 4s. They also give readings at different rpm's as well. Snap On produce a good one.Be pricey though.

Danger

1st July 2008, 19:08

To save time from repeating myself please review the following threads. :whistle:

http://www.kiwibiker.co.nz/forums/showthread.php?t=70119
http://www.kiwibiker.co.nz/forums/showthread.php?t=65320
http://www.kiwibiker.co.nz/forums/showthread.php?t=64716

It helps when jetting to mark off on your throttle with some masking tape 1/4, 1/2, 3/4 and full throttle positions so that you can target the circuit that is giving you problems with the correct jet.
I've said it before, plug reading is only any good with a new plug, a bright light and a magnifying glass to read at the base of the porcelain for instance after a full throttle run under load up a hill and a throttle chop. As soon as you go into a different throttle range or jetting circuit incorrect readings will be shown. How do you know where in the range your bike is rich from reading an oily plug? That might encourage you to go lean on a circuit which is already lean resulting in engine damage.
Also burning oil on the plug will result in all sorts of colors throwing your results off. It can be used as a rough guide to indicate that yes the bike is rich or lean somewhere in some circuit, but because there are several circuits that overlap each other it is off little use beyond that in my opinion unless using a fresh plug for each run on just that circuit that you are having issues with.
So I guess I'm saying opposite to Reckless that I jet a 2 stroke by feel, rather than plug readings. Doesn't mean I won't look at a plug but I can feel when a bike is rich or lean better than any info I can get from a plug.

dammad1

1st July 2008, 19:30

Reckless

1st July 2008, 23:35

ok I agree with the articles about the procedures etc 100% especially that article about more oil more horsepower. But I can't agree that you can make a jetting change decision without reading the plug. In my opinion you cannot decide what to change by feel alone. Feel will tell you its not right or if its better but what to change and where its needed. I believe has a lot to do with how its running now and you tell this more than anything by plug reading. If your going richer you will get away with it but if your going leaner that's very Dangerous (hehe excuse the pun)
We tried that on our karting engines and seized quite a few. In all the time Robert Taylor read my mates and my plugs, he never once insisted on a new plug to get a better reading. I don't know why, but he is very good, it was a few years ago though. But we where hammering our engines very hard and coming in hot. We had high compressions, no clutch baskets at all, moto plat ignitions, egt and cht sensors, Fully adjustable power jets etc. Every jetting change decision I saw Robert make, and we made, was based on what he/we saw in the plug.
It went like this. Robert it doesn't feel quite right out of corner at 1/2 to 3/4 its flat today? Lets see your plug? O'K try one clip down, or try one size up on the main or try the other needle, was generally the method. In fact we never went near him without the plug in our hands and I can't ever remember him making a decision without looking at it. In those days he was the 2stroke maestro. So all I can go by is what I have experienced and been learnt. Hopefully he doesn't come on and tell me I can't remember anything he showed me properly and to keep my uninformed mouth shut!!! LOL!!

Also do cheese and I need that sort of exactness in the sort of riding we do. I personally don't mind mine being a tad rich so it runs cooler, doesn't quite need to be "on pipe" so much to go well and the maintenance periods can be longer. I would suggest we have all the power we need with what we have now. I don't run a black, wet, horrible, shit encrusted plug, but its not 100% on song everywhere either. And the thing still scares the shit out of me sometimes.

Again, I agree with 99.9% of what you have said but leaning off by the seat off your pants. Sorry guys but I couldn't go there.

Danger

2nd July 2008, 08:17

Its not difficult when you go from 24c and humid to 16c dry to determine that the bike is going to run leaner and you need to richen your jetting. I suspect Robert was confirming that you were not excessively rich or lean when looking at your plug. I might do that myself if someone came to me with a problem with their bike on the day, a bike of which I don't know its history of jetting changes but again if the rider has not messed with it all summer and its been running fine but now its pinging and I say how did it feel last week at 24c and you say it was fine, but its cooler today and pinging I'm definitely not going to tell you to go leaner, that would be Reckless (touche).
Its obvious that it needs to be richer. Air screw is the first adjustment. If the airscrew gets to 3/4 turn and still lean fit the next richer pilot jet and readjust the airscrew. If its still pinging after 1/4 throttle richen the needle position.
My plug goes in and stays in until I change it when I change over the seasons jetting so it only comes out twice a year at the change over. I don't pull the plug every ride to check and adjust the jetting. I will adjust the airscrew on the day when I feel it is too rich or too lean (I keep a note book with the bike with temp, humidity, fuel ratio, venue and airscrew and other jetting specs to refer too) but I will not pull the plug to confirm what I feel and know because by then the deposits of burnt fuel and oil will not tell me much that I can't feel or just know from the changing conditions.
Now if I have a new bike and I'm unsure if I have the correct needle I will remove the main altogether, dial in the pilot and airscrew first, then the needle, test ride, readjust the airscrew if needed, then fit a rich main (I know what rich feels like up top because I have run the bike without a main) and then keep coming down until I feel a lean symptom then go back up a size. Subsequent tests might indicate I go up another size because it suits our conditions (under hard throttle in soft sand). I like to run a slightly rich main for summer, winter the sand is not as hard on the bike and the main can be closer to optimum.

Its not brain science, or is that rocket surgery?

Beware the advanced timing on many two stroke MX bikes can cause a lean type feel with knocking. Many can benefit from slightly retarding the timing and it suits the power delivery for off road riding better than the stock timing setting used for MX.

Another thing, if you run a inline fuel filter between tank and carb these do clog (thats what their for to filter debri from your fuel) and you may feel this on a full throttle run for a period of 10-15 seconds or more. So your bike may run fine everywhere else but you might get out to that hill over the back of the farm trail ride where you are giving it the berries and all off a sudden the bike is going lean like its running out of fuel. I swap them out for a new one when I change my jetting for the season and the plug, so only use them for 6 months. Otherwise they may cause a lean condition up top.

camchain

2nd July 2008, 13:00

Great interesting info (for someone like me looking at re-entering 2t world) and mixed with some fun banter as well. First rate. 2t jetting really is a mixture of art and science.

Seems to me a fuel injected 2t with different maps would be an interesting beast (This is just a brain fart - no flames please)

The other spanner in works to balance is of course altitude. Not a big thing for most riding in NZ but where I started riding on the volcanic plateau (a fair bit higher than sea level) bike would run different here and there. Be interesting to know how high up Tarawera 100 is for instance? Something to bear in mind anyway.

Reckless

2nd July 2008, 13:55

Na Robert would look at the plug even if it was the 10th time he'd looked at it that day. He seemed to be able to see the difference the last change had made, we could too, to a degree after a while. You know what its like, always after more horsepower. Surprising we didn't drive him crazy actually. When he wasn't there we'd do fine but when he was. He was always pestered by guys (including me) other than the one he was meant to be there for. He was very good about it actually.

The warning about the advanced timing is very valid as we used to run special ignitions to advance the timing. And now and then we'd go too far and get detonation. I have even seen the side completly worn off the piston by the exhaust port. We had specially modified brackets (modified plugs) so we could set up a dial gauge in a very short time. So if bikes are now set up with advanced timing standard for more top end the line will be getting finer and a timing adjustment for X country will be quite effective.

Filters! I agree 100% here. I don't run a filter on my bike (don't know why really) but if I had a dollar how many times we fixed a porblem on someones Kart by removing the filter I'd be rich. Quite often they'd get clogged with fine white hair looking stuff, might have been in the Methanol, it was a shit for blocking filters really quickly.

Danger we are probably talking about 2 slightly different ways to skin the same cat. I generally do it same as you have described except constantly use the plug as a reading/yard stick.

Each to his own I suppose:girlfight:

Danger

5th July 2008, 10:32

Here is an example of the correct way to read a plug for jetting purposes. This is the result of a 4th gear plug chop on a new plug. Once the new plug is fitted you need to start the bike and accelerate at full throttle up through the gears for 15-20 seconds then pull the clutch in and hit the kill switch and immeditly pull the plug. A hill is ideal for this and it needs to be somewhere that you do not have to throttle off for a corner or what have you.
The area you need to check is right down inside the plug at the base of the porcelain. This is where a bright light (a pen light will suffice) and a magnifying glass come in handy (if your eyes are good like mine you will be ok).
This is called a smoke ring (also known as the mixture ring).
If the smoke ring at the base of the porcelain is about 2mm and a light chocolate color, congratulations you are jetted very close (or correctly) at this throttle setting (main in this case).
If the smoke ring at the base of the porcelain is less than 2mm, white or very light brown you are lean.
If the smoke ring is more than 2mm at the base of the porcelain or is black, or dark brown you are rich.
You need to use a new plug for each plug chop.
The tan color near the electrode is the result of the burning of the fuel, oil, air and petrol and is not a good indication of jetting, there will always be deposits burnt in this area (unless your plug is so hot that everything gets burnt off this area, perhaps a very lean condition or incorrect heat range plug).
Once you are jetted close on all the circuits then fine tuning can be achieved if needed for your conditions and riding demands over time and by feel.
I typically only use the plug chop as the final test to check the main once the other circuits and the main are dialed in by experimenting and test riding. But it can be useful if you are not that tuned into how a bike should feel by riding or are unsure if what you are feeling is richness or leaness.
Sometimes you just have to put up with a bike that is not jetted at the optimum for the days ride. Jetting is a moving target. For instance I rejetted my KTM only a few weeks ago because it has been quite warm and air screw changes have been adequate. The last few weeks have cooled somewhat so I switched over to my winter settings and because I maybe riding in Taupo soon (different bikes have different change over temperatures, my RM started running lean several months ago and was changed to winter settings then).
Yesterday at the Sandpit it was damp but warmer than the last few weeks. I felt a little rich of idle, but because we were pinning it all day it wasn't a problem and I didn't make an air screw change. If I was putting around I would off. My summer jetting specs would have worked fine yesterday all be it with a rich air screw setting, but I'm not going to pull the carb and change over all the jets depending on the day. The winter jetting would also have been fine with a leaner air screw setting, which would have taken only 10 seconds to adjust back at the carpark but I forgot and only noticed it rich towards the end of the day as the day got warmer and the humidity climbed with the approaching weather. Chances are the next ride will be cooler again and the jetting will be perfect with the correct air screw setting.

Danger

5th July 2008, 11:10

A little lean.

Danger

5th July 2008, 11:11

A little rich. But notice the nice tan color at the top? Would indicate all was fine if using that method to read the plug.

Danger

5th July 2008, 11:17

You might look at a plug like this to check you are in the ball park, but as we have seen in the post above all is not as it seems. The plug does not just remember the last throttle setting it was run at. You could be rich on the pilot and lean on the main or vice versa to get a plug looking like this. Useful for a commercial mechanic trying to get his tractor running right, but not good for a high performance seeking motorcycle racer.
Different fuels and oils will also give different colors. Its the smoke ring that tells the true story when reading a plug.

Reckless

5th July 2008, 17:21

Great write up Danger pics and all. That would have taken a bit of your valuable time should help a lot of people though! A lot of guys would not have wanted to part with their knowledge so freely!

"edit" Just had a thought! Not taking away from what Danger has taught you all! But if your not trying to get the max out of your bike in every area or as serious a rider as Danger and the others. The tractor plug is not to far off as long as your bike is pulling well from closed to fully open throttle. I run mine a bit richer than that, I don't foul plugs and the bike still has more power everywhere than I need. Danger prob would think my Ktm 200 was sick, as I have the power valve backed off quite a bit as well. But for my level of ability its better than fighting a race horse every time i ride! Its smooth right through the range and anymore power and I ride like shit! I've only been riding MX 3 years and I'm old so its best to match the bike to the ability.
As a general rule on used plugs the centre electrode color tends to indicate Main or top end and the outer (steel) ring tends to indicate low range. So on a used plug if the outer and inner (as I call them) are both dark and wet you could lower your needle a notch to lean the mid and top. This drops the needle further into the Emulsion tube at full throttle and drops the taper as well delivering less fuel/oil and leaning both areas a bit.

But now we are getting into plug reading used plugs, and that is not what Danger is teaching. He's teaching how to get optimum set up for your bike through out the full throttle range. And he is correct if you set your bike up this way you should only have to look at the plug for safety to make sure its not Grey/white and your lean enough for a seizure. Thanks Danger!

cheese

5th July 2008, 20:05

My plug is just black as black.....