1991 KX125 testride

Re-jetted it (Re- jetting a two stroke involves changing the jets and needle height in the carburetor while checking the color of the spark plug between runs until the plug is tan colored and the engine is responsive and powerful.) for summer and a stock head instead of for autumn and the milled head that was on it. Pulls strong and gets through the gears fast. Still doesn't run as good as it did with the old head but at least the head gasket doesn't leak anymore. T re-jet your two stroke you need to get a few different sizes of the main jet, the big one in the center of the float bowl in the bottom of the carburetor. You can also change the pilot jet (idle to mid range) if it doesnt want to idle correctly. Typically on a two stroke bike that has had mods like exhaust, air filter, reeds, piston; you will need to lean the pilot jet(low rpm) and richen the main jet and needle (top rpm). My KX125 started with a 145 main jet and I went up to a 180 at one point, Now has 160 or 168. My needle is in the 3rd clip position (middle). I encourage you to search on google for information on rejetting your particular model.

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[19boykin]

i have the same bike too, ive been mixing it 32:1 with regular 87 gas. should i upgrade to the premium gas?

[supra60]

@19boykin It is a race bike. You should run premium fuel in it. Two stroke engines that have had porting and compression increases require race gas to avoid detonation. Detonation is deadly for an engine, it causes sparkplug insulators to crack, ring lands to crack, piston crowns crack, headgaskets to leak, etc.

[46000rpm]

how much did it cost to have it rejeted. my bike keeps fouling the plugs . it all wet when i take it out.

[supra60]

@46000rpm

I did it myself, the new jets are pretty cheap. You really should check the reeds and the carburetor boot for cracks and clean the carburetor and clean and re-oil the air filter, repack the silencer and then go about rejetting it. It is a high maintenance bitch like all dirbikes.

[skateVA]

hey man nice bike! i have a 92 kawasaki kx125 that as of this weekend needs rebuild. the guy i bought it from didn't know shit about it but it has always ran at 52:1 mixture. when i rebuild i plan on doing a 144cc big bore and i was wondering if you could give me a few pointers such as how to tune the carb (needle height, main jet size, air screw) and also where can i get some cheap, high quality jets? thanks

[supra60]

@dirtjumpbmxer You shouldnt use that fuel in a two stroke that you have to premix fuel for. Try to use only premium petrol (91 octane or higher) since this is a racing engine...

[46000rpm]

how much did it cost to have it rejeted.

[ventureskatr]

i have this same bike and year and i dont know if i should sell it..im selling it bc its so old ..you think i should sell it or fix it ..its having carburetor problemss:/

[supra60]

@dirtjumpbmxer If youre lucky you might get away with reusing your cylinder but if its not any good you better get it sleeved or replated. And make sure that its not running too lean, thats mostly why mine would lock up and overheat and blow head gaskets. Educate yourself and save some money. Thats what i had to do.

[supra60]

@dirtjumpbmxer It used to when I first got it. Someone modified it to run higher compression by shaving the head. I put on a new stock head and torqued it to 18 ft lbs of torque and always run 93 octane fuel mixed 40:1, and its fine for the past few years. You will have to get your cylinder repaired if it has blown the gasket. I advise you to look up a book by eric gorr about tuning mx bikes. It has good info about these bikes. sign up on amazon and you can read parts of the book or google it