I got a 2006 KLX250 and the PO had did some work: breather mod, open airbox, and changed the main jet to a mikuni 132 and 40 pilot. As far as I know, there is a stock needle. Exhaust is stock. From what I am reading, this seems way too rich for sea level. Dynojet recommends a 124 for the main. Should I change the main jet? to what? Can any harm occur from running a 132?

 

It sounds as if it were too rich but how is the bike running? Although checking the plug is not a very accurate why of checking your jetting it will tell you if your running way to rich. If the plug is greasy black I'd drop the main to a 128 or a 125. Put in a new plug if you do drop the main so that you can check that one once you run the bike for a bit.
Your looking for a nice brownish tan color to the electrode.

 

The Aus bikes get a #132 main jet and a #35 pilot from the factory , works great with the stock airbox/filter and muffler set up. Leave it alone if it's working for ya. Don't confuse Dynojet jet sizes and the OE Kehien jet sizes, they're different.

 

Not sure how it runs yet as I havent had a chance to take it out yet...i talked to eddie sinseros from KLR650 and he said just use the same jet numbers when comparing mikuni and dynojet jets...he said the comparison chart is useless s thre are other factors besides jet hole size that matter...the PO said he checked the plug before and it looked fine.......i read that u have to use the throttle chop method to get an accurate reading from the plug though

 

Yes that's how you do it but it's not very accurate nowadays.