Ffffed up the jetting on my rm125

no it is not a good subsitute..........unless you dont mind breaking off the electrode and rebuildoing the motor!!! The rm bikes have vibrations that cause the electrode to break off.

Search for the word jetting on this forum. There is a ton of info on this forum. Having someone type step by step instructions is redundant. Turning up your idle before attempting to start the bike won't do a heck of a lot. Turn the choke on, then start the bike. If you turn up the idle, all that will happen is once the bike starts up it will idle fast. You do have jetting problems. It is running too rich. Re jetting involves getting into the bottom of your carburetor bowl, removing current jets, read the number on them and then get smaller ones. If you are comfortable doing this, go for it. - Keith

If you mix two different oils together you are asking for a fouled plug.

Dale

dales298 said:

If you mix two different oils together you are asking for a fouled plug.

Dale

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Unless you are mixing significantly different oils, this unlikely. Virtually all modern oils mix without issue, unless you are trying to mix castor and synthetic or something. It is better to use the same oil for consistency though.

Poor jetting causes way more fouled plugs than the oil used, or the mix ratio used.

As to whether you can adjust your mix ratio and play with the air screw. No it will not lean it out. Going to 40:1 will actually richen the jetting slightly, and make your problem worse, not better. The air screw will only lean out the pilot circuit, not the needle, or mains, so no, you have to rejet the bike properly to solve this problem.

Get some fresh mix with only one type of oil, a box of plugs, and jets a couple sizes smaller than what is in there now, and start tuning until it is correct. There are very good instructions floating around here on how to correctly jet your bike, run a search, find them, and then tune your bike from there.