Jetting a rm125 '00

[pyromaniac]

The sparkplug is black and it doesnt want to rev "clean". Its hessitating and i think you call it sputtering. The jetting worked fine when it was around +2 degrees. Today it have been -1.5. I think the weather will be around zero to -10 most of the time in the next weeks. Maybe it will be around -10 to -20 and then i still want to ride.

I dont know what jets there in now cause i havent changed them since i got the bike so i think its stock. But i guiss i should go, how many steps? smaller. Not knowing what jets there is now what would you think a good setting would be for my weather?

 

[pyromaniac]

I forgot to say im rindng around sea level and the gas i use is 98 octane pump gas. Anything else you want to know?

 

[TRAIL]

Try one size smaller main jet

 

[pyromaniac]

I couldnt wait till tomorrow to check the jets so i went out now(2am). The main jet i 175 and the pilot is 50.

It worked fine in +2 degree with this jetting and not now when its -2. It should be running leaner now but accoring to the plug wich is wet and black its running rich. Maybe the pilot is too rich and the main jet too lean. I guiss i have to try around.

Lovering the main needle isnt that the same as going for a smaller main jet? Is needle just for fine adjustment and the jet only changed then the needle clip is on top or bottom and need to be even more richer or leaner?

The bike starts on first kick as it use to do(if i have a clean plug) but doesnt rev as much as it use to when starting with choke - why you think? Then it dies after like 10 seconds or if you try to rev it it dies. When it dies the plug is wet. If im lucky i can get it to stay alive and carefully rev it. When it once reved out it i can keep it going but when i kill it is still have a wet plug.

Usually how many main jets and pilots do you use to have to jet your bike for any weather? I mean whats the biggest and smallest jets you have had in the same bike. Just so i know how many i should buy - i rather buy all at once so i have them when i need them rather than stading with a bad working bike on the weekend when the weather have changed.

 

[Fark]

Hello friend. I understand english is your second language. Please ask if you don't understand anything, I'll be glad to help you. You seem to speak english well though! Here is some help:

If you lower the needle, it will feed the motor less fuel from 1/4 to 3/4 throttle. When I say lower the needle, it means for you to remove the clip on the needle and install it one position higher. This will make the needle sit lower and block some fuel from entering the motor. The needle shuts off after about 3/4 throttle opening; then the main jet takes over.

Just like anything else, a carbueretor is a system and all parts must work together for good results.

A 50 pilot is stock. Most bikes are set rich from the factory so I'd buy 4 jets" 2 sizes leaner on the main and pilot. Now, there is a pilot screw. It allows you to fine tune the pilot circuit. It only works from 1/2 turn out to 2 turns out! You're bike is probably set at 1.5 turns out. Though I would not touch that yet.

If I were you, I would install a plug that is 1 heat range hotter first. You may even be able to get away with 2 heat ranges if it's -25 deg F there. These bikes were designed to operate in 70 degree weather. Most come jetted rich from the factory and with too cold of a plug to prevent engine damage. Since colder air has more oxygen, your bike may be rich enough. I think that your plug may be fouling from the cold air. If a plug doesn't operate at a high enough temperature, it will accumulate carbon and the spark will not fire where the ground arm is, the mixture won't burn.

Now, if you run a plug too hot, you can cause engine damage from preignition. If it is really -25 deg F there... you can probably go down 2 heat ranges safely. But see what happens one heat range lower first. The plug should resist fouling better.

If your plug is wet you won't cause engine damage by going down one jet size. I'm willing to be the bike will fell better with less fuel. But to be safe, let's try a hotter plug first since it is very cold there. In theory, colder air requires more fuel, hotter air requires less fuel. Hotter air requires a cooler plug, and cooler air requires a hotter plug.

A cold NGK plug will have a number 10 on it. The hottest plug will have 1 on it. So look at your plug, and order a couple with lower numbers. So if it's an 8, get 6 and 7, and try 7 first.

What you need to do is start ordering stuff by mail. I like www.denniskirk.com. You may be able to find better deals on plugs there and you can order a few at a time.

 

[pyromaniac]

The strange thing is that the shop said there is only one sparkplug that works on my bike and its the one i got. Its a special sparkplug thats why it costs so much there. Sounds kinda strange if thats the case but i think he know what he is talking about. Its a number 8 plug. However ill go to town to buy some jets.

 

[pyromaniac]

The 40 to 50 pilots were sold out. So i bought one 38 pilot and a 178 and 180 main jet.

First i put in the 38 pilot and it made pretty much difference. The bike never died since, much less smoke, almost nothing. With this change its still not reving out completly and its hessitating in mid revs, less than 1/4 throttle. It revs out when riding it but not when in neutral.

Then i installed the 180 main jet and i cant see much difference, still not want to rev clean.
Running a few minutes on the lake with the 38 pilot seem to have cleaned the plug, its not brown or black its just like new. However when i got back from the lake i installed the 50 pilot again. Started right up and worked fine, more smoke but no hessitating on the low revs. Seems like this pilot works fine now when the plug is real cleaned, maybe it will get black and bad after a while. I will buy more pilots in between the 38 and 50 range. I think it will be fine then with a pilot around 40-45.

The problem is still the top. I dont know if i should go leaner or richer cause it didnt show enought change from 175 to 180 to judge which is better. I will buy both richer and leaner main jets to try it out. I think the hessitating is a sign on too lean jetting.

Do you have any good tips on how i should see if its too rich or too lean?

 

[Luft]

Pyro: what is the brand and part number of the special plug you are running? Is it different from the original plug that came with the bike? What type oil are you using on your air filter? What tpye oil are you using and what ratio are you mixing the oil? Have you checked the level of your transmission fluid lately? Before you go any further please check the transmission fluid to make sure you are not losing fluid through a bad crank seal. Are you temperature numbers in Celsius?

 

[Fark]

Yes, good advice luft. I too am curious about the actual plug number. I don't like dealing with dealers. I had one tell me I had to use their 10 dollar platnium plug. I bought it but never will I trust them again. They are there to make money. Most dealers I find don't care to listen and think they know it all. That's a whole other topic though.

So what is the make and number of your spark plug?

 

[Luft]

Fark: I had never used a projected nose plug before I found out about them on this board. I did some research on the web and decided to try one. We have a KX 65 which we have been using a B9EG and contiuously foul them. I called the dealer and asked if they had a BP8ES in stock and they said yes. When I got there they showed me a BPR8EG and a B8EG and said the guy said the mechanic said they were the same. I told them they were not. They then found a BP7ES and I took it home. I measured the plug hole for piston clearance to be safe and then we tested it. My rider works in the lower rpm range and always fouls plugs. Not with the BP8ES.

 

[pyromaniac]

It is the stock sparkplug its a NGK i dont have the partnumber now, ill give it tomorrow. I dont think its a "dealer" thing cause they said you CAN on your own risk use a NGK B8EG. Its because of the 3D ignition the 00 and 01 rm it have this special sparkplug. This is the kind of thing that make me not like a brand, stupid things that just costs money :)

However the spark problem seem to be fixed, the bike havent died or have had a wet plug since i ran the 38 pilot, even after switching back to 50. So now everything seems fine except what i think is too lean main jet. I read on eric gorrs site about jetting and he wrote that if the bike make a boooowah sound its too lean and i think the sound is pretty close to boooowah :)

I will check the gearbox but i dont think its anything wrong there. The airfilter oil i dont know cause i havent made it dirty since i got it - it was new oiled but i think its probably twin air. The temperature is in celcius.

 

[Luft]

The hesitiation on top is from being too lean, increase the main jet size until you can determine that it is too rich, the exhaust will make a blubbering sound. Continue to experiment with the jet sizes to experience rich and lean. Find what makes the engine pull the way you like it. The airscrew can be adjusted in to richen the pilot circuit ar 0 - 1/8 turn throttle and outward to lean the circuit. You will be pleased that you have made this effort. Stay with the plug your dealer has recommended for the moment.

 

[A-RustyDemon]

Is the plug like a R6918B-8 Because my Suzuki dealer said that the factory told them that is was ok to use the BR#ECS plug as a alt. plug. It's a doulbe grounded plug. But I just use BR#EG's and EC with not trouble. But that's a choice I make. but then again I'm not racing either. Just a thought. And to clean mine up I had to run a 168 main a 42 pilot with a R1470MS needle clip on 3. But as the weather changes so does that. largest main change is a to a 175

 

[RemeberMe]

Pyromaniac

To check the main jet get your bike up to operating temp and then run it down the street. On the way back to your house get your bike into (the bottom of) 3rd or 4th gear and hold wide open throttle for a good distance. Hit the kill switch without closing the throttle and coast back to your house. Now, pull the plug and see what reading you get. Let us know what you find.

 

[pyromaniac]

Sorry i forgot to check the plug number today(been doing other stuff) but i think its the R6918B-8 one, pretty sure. I will hopefully get more jets tomorrow, if so, i think it should be enought to get the bike running good again.

I hope i dont need to rejet everytime i want to ride. It can change over 10 degrees from day to day. But in other hand if i rejet my bike everytime i go riding i should soon be a star on it. Maybe i just need to lick the finger and put in in the air and feel today its 182 45 that will make the bike rock :) Maybe not. I dont like the idea that i may need to change jets once every second ride or so. How often do you usually need to rejet?

 

[marcusgunby]

I only rejet for winter and summer-i put up with small variations in temp-the airscrew is very uslefull for changes in outside temp.In fact the airscrew is the most important adjustment out of all the jets-its the easiest to alter and yet the most ignored.

 

[pyromaniac]

I got six new jets today and i have tried them out. The upper rpm hessitating is still there, with everything from 165 to 190 - i guiss reving it in neutral is not the right way. I remember the bikes often use to sound bad when doing this but working great when riding. So i will try different jets while riding the bike instead, tomorrow.

Its been around -12 to -16 today while i were trying different jets. I dunno really what to think, trying to jet it and just test is by reving in neutral is just not good. But changing jets and then ride it is a bitch, i can just about get the carb out when i removed the whole subframe. Thats what i really hate about new bikes, its so damn tight. However on the lake it should be no problem riding without the airbox in matter of dirt cause there is only ice and snow - its another thing that if i try to sit down or in any other way toughes the rear wheel i will be piece of meat.

Oh well i guiss ill take my tools i need and all the jets and spend tomorrow on the lake bitching with the jetting until im happy.

 

[A-RustyDemon]

Good luck and try to have some fun

 

[pyromaniac]

I went to the lake but i never changed any jets. I was quite happy with the bike as it was.

Only when having the throttle on a specific opening and i turned it wide-open, it hessitated a little, maybe just need to change the clip on the needle. Otherwise it was great, felt like it reved just as much on maybe 30% throttle as wide-open - the only difference being how much power it made. So when i got the speed i wanted i could just open the throttle slightly and the rear wheel slided though the corners. Man it was fun!, controlled slides in last gear for just as long as the corners were(it was a track they hade made with the cars) if there were no straights i would slide the whole lap! I was -15C so i was a little cold in feets and hands when i got to the track but once i start riding i didnt freeze but i had to wear i "robber mask" cause any skin exposed to the wind will freeze. Once riding the exitment make the blood flow and warms every part of the body.

About that hessitating i have described when in neutral. I heard the exact same sound today when i saw the guys on a indoor freestyle show reving to the crowd, and i guiss their bikes are setup right.

I think the next test to see if the bike is jetted correct is to go to the MX track. On the lake it never have much to work with, no slopes or deep sand. The bike may act different when it have more to work with, should be easier to feel if it doesnt pull.

I also checked the gearbox oil level and it was ok. Im running 180 45 and another sparkplug instead of 175 50 when the bike just didnt want to go well one day. I think the sparkplug is the reason it didnt want to go very well. However im still not quite sure the jetting is good cause the sparkplug doesnt want to show much color.


Well happy new year!

 

[pyromaniac]

I was out riding today and it worked fine, -7 and a little snowing. 45 180 on the jets. The onlything i can complain about is when riding on very, almost idle, rpm and opened the thottle(fast) more than 1/2 it bogged. Its very unlikly that i will ever be affected by this when riding and not just testing. But it would be fun to know what may cause this, any ideas?

 

[Fark]

I don't know if that's avoidable. On street bikes, the throttle is actually linked the throttle blades... and engine vaccuum lifts the slides. They are tuned so even is you wack the throttle, the slide will move up smooth and prevent bogging.

But... that's an entirely different animal. Probably not even relevent.

 

[pyromaniac]

I were riding today and tried to use the choke to see if it were running lean or rich. The result was that the bike didnt run much worse. In normal case it would run real bad or most likly just die. Is this a sign of too lean or could it have something to do with that the engine(spark or whatever) never really gets optimum operating temp?