Jetting a rm125 '00

Try one size smaller main jet

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.

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?

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?

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.

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.

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

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.

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.

Good luck and try to have some fun

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.