Rm250 running rich.

[Lion]

alright i think my bike needs a rejet. it fouls plugs quite often, and is running crap up in the powerband. the motor is only about 15 hours old, so I dont think its an internal problem. the jetting is stock and the only mods the bike has is a set of aftermarket reeds and a fmf exhaust system

when I get up into the powerband, the bike doesn't feel like its making any power, it revs fine, but just isnt making enough power. does this sound like a rich condition? if so, can I just raise/ lower the needle clip or do I have to do a rejet?

If a rejet is required, how much would it roughly cost to get it profesionally done?

[Danger]

What year is the bike? If you have made no jetting changes it is more likely running lean at this time of year. Colder weather makes your jetting leaner. Warmer weather makes your jetting richer. Fouling plugs can however be a symptom of rich running. I have an '05 RM250 so tell me your year, the jetting you are running, oil type and ratio, and spark plug because I might be able to help for a blat around your track sometime.

[Lion]

hey I am running 40:1 castrol tts. Year is a 1996. Funny thing is when I first rebuilt it the plugs were a nice tan color, and now they get fouled after a few hours of running. dont know whats up with it??

[Danger]

Try adjusting your air screw first. In is richer, out is leaner. Check where it is set from fully seated (lightly). Try coming out about an 1/8 of a turn from where you are set.

[davereid]

Air Filter may need sorting, bike wil run very rich if aircleaner is dirty/blocked.

[Lion]

ok sweet as will try both of the above. just wondering if faulty powervalves would cause these symptoms?

[Lion]

Well I cleaned and re oiled the air filter, but there was no difference. Also noticed that its really overfueling as there is a mixture of black & blue smoke. How much will a shop roughly charge to sort my bike out?

[F5 Dave]

Hard to say but I expect expensive, really most bike shops are not set up to do it unless you find an Mx keen mechanic it is best to do it yourself.

So it used to run ok, but then you changed the reeds & muffler?

Always a story behind the initial one.

For another starter try cleaning out he carb & check that the float isn't leaking, all airholes are blown through (never poke) & check the tube the needle goes into isn't ovalise (a small amount will be an issue). Is the slide worn?

Rebuilding the engine may cause more suction that make cause it to run richer, or fixed an airleak. Aftermarket reeds tend to make things richer down low.


There are heaps of articles on line for jetting 2 strokes, read up & try.

But here is the thing to remember when jetting this type of carb. Think of throttle position, not revs. Write this down & look at it before making any changes.

Remember it is possible to be too rich on some jets & too lean on others.

[Lion]

Nope havent changed reeds or muffler, bike came like that. Plug was a nice tan color when I got it. I have some spare jets that are a few sizes smaller. Will try out the jets and get back to you.

cheers