2001 125MX ignition and jetting

[Taffy]

Hello

I have a 125MX here, a real minter, very pretty indeed in red. I've just rebuilt the engine using a YZ125 rod kit and a wossner piston. the rest is standard fair. it has Boyesen reeds and a new and rare DEP pipe on it. It has a Kokusan ignition and word came to me last night via a photo I sent to Steve Hardaker at Bradford Ignisions that it looks very similar (off hand) to an RM125 ignition from the early naughties. however, the only manual we can get (from a 2003) indicates that they swapped immediately to someone else or at least just the set up because the ignition pick up is 180d away! explain that!

I have been rebuilding it and we have two wildly different jetting maps and problems getting to know what the correct ignition timing should be.

we think that it should be timed at around 1.6mm BTDC but can anyone be sure?

we have two sets of jetting figures:
one set with a 7 cutaway and a 40PJ and the other with a 5 cutaway and a 45PJ. completely different directions!

at the moment we can only get it running on the #5 and a 40PJ. we are ready to close it up bar these two things?

I can strobe the ignition timing or old school static.

anyone else got one of these and any info?

regards

Taffy

 

[Zman]

I have seen several 2k2 flywheels that look the same, but if you look closely there is a difference in the relationship between the keyway and the reluctor pickup (bump).

You can check the jetting database and you may get close by following the jetting that worked for others but there are so many variables you really need to do the work to jet your specific bike for your location, weather and riding style. Engine variables (compression, port timing, squish, reed type, ignition timing, exhaust variables) Carb variables - (float height, jet variations,etc) riding location altitude, humidity and temperature all affect the jetting. To make matters worse the GG 125 has a large 38mm carb so it a bit more difficult to jet correctly for it to run right.

Depending on your intended use of the bike, you may want to consider swapping the 38mm carb for an older 35mm PWK off of a kx125. We have two GG 125s and the smaller carb made a big difference in the low end torque, overall ridability and the bike is less susceptible to weather/temperature changes. As far as I can tell the high rpm top end did not suffer.

Good luck