Mikuni carb tuning help needed
 

I have a 1992 RM125 with a Mikuni TM carb. The bike doesn't run, and I know less than nothing about it. Where do I start? Anyone have suggestions for a baseline? I do have a 36mm AS2 available if all else fails, but I want to win honestly. No cheating! Well, not yet anyway.

Thanks!

Is this a new combo or was the bike running previously? Can you tell us the jetting that is in it now?

You say the bike doesn't run...Difficult to say where to begin...

Has the bike been stood a long time?

Does it start at all?

Do you have a spark?

Is there compression?

Is the plug wet/is fuel reaching the plug?

Does it fire at all when you try to start it?

Same as where I started with my Husky CR125..

What do you want to know/check? To see if she'll run, first at least ensure the air filter is clean, and the carb is flushed clear and no jets blocked, make sure the engine turns over, that you have spark, and compression. Even if poorly tuned it should run (poorly).

If you can't get it to fire you'll have to dig further depending on what you find. No spark, look at wiring looms and stator, etc. No compression, start pulling engine. Don't forget reeds too.

If you get to the point where it's going to start costing $$ to get it to fire, you'll need to start looking to see if it's worth it (the state of the rest of the bike and other possible money suckers).

When you pull the carb down to clean it, check the float height, and take note of the jets and needle installed. It'll also give you information to work with in your research.

Spark= Yes

It ran before, at some point (allegedly). I just don't know how the Mikuni TM functions. I'm heading into the shop momentarily as mom and the kid are occupied and I'm given a little freedom. I'm just looking for "this does that" as we already have for the Keihin, I guess. Needle position, "this many turns out," and other odds and sods for the TM. I'll dig into it as my hands are a bit too clean at the moment and figure out exactly where I am with this, um, bird. Like a first date, if you will. "Don't put your hands here, mate, likely to get pushed off."

And, as posted prior, I do have a "known" 36mm AS2 for offer to this fiend. but if I can get the TM to cooperate, well, I'm ahead of the game.

It's same same mate in terms of what does what.

They just use different needles and jets, but the theory is the same.

As above, give the carb a good clean and note what is in it. Try and get it running and then you can get a baseline to start tuning. You should also be able to google machine up a few threads on the matter and see how what you have compares to what others have ended up with.

Same rules apply that if you need to jet well outside others specs you'll more than likely be compensating for some kind of mechanical issue.