Kawasaki Z125 transmission repair: missing shifts and popping out of gear. (Part 1 Video)

My friends recently competed on my Z125 racer. I bought the bike ~2 months ago, used. I have been converting it back from being a lowered and stretched street bike into a competitive road racer. The bike has been raced with TMGP mini road racing. Since beginning the project there have been lots of things to correct and fix. We’ve had the bike out only a handful of times before the race to try to sort it out. The biggest liability right now is the transmission on the bike. It does not work acceptably. Here are a few videos from their Race and some pre-race testing:
   • Kawasaki Z125 trackbike setup work: unride...  
   • TMGP - Final Endurance Race 2025 - 11/01/2...  
   • TMGP - Final Endurance Race 2025 - 11/01/2...  
Part 2 Video after repairs are made here:
   • Transmission Working! Factory Pro shift ki...  

Today was my first opportunity to have any time to tackle this. I’ve started with some upgrade parts to hopefully help it work better. The parts include:

1. A new shift lever that does away with the shift linkage that the stock bike has.

2. new shift detent arm that I got from Factory Pro in California. This was a rather expensive part for what it is. What it adds is a ball bearing on the end of the detent arm which tracks around the shift star on the shift drum. Significantly less friction. (Is that a good thing?!)
http://www.factorypro.com/index.htm

3. The final change is putting new oil in the engine and switching to 20W-50 instead of the original 10W-40.

In this video, I also replaced the clutch. But I think this was a complete waste of $$$/time and doesn’t really add anything that will help with the shifting and missed gears. The stock clutch shows superficial wear at only 4k miles. I was unde the false impression that what I ordered was a 6-plate clutch pack which is 1 friction disc more than a stock kawi. Turns out that was not the case. Well, I had zero expectations that this would fix the gearshift, I included it since I had to take the bike apart anyway, and it was a good time to make the clutch more durable by adding the additional clutch plate. Which it didn’t. The only plus is the clutch did come with 30% stiffer springs. Since I already had the parts, I followed through and completed that job.

Next week, I hope to actually ride the bike and see if we have problems missing gears or the bike popping out of gear. If it continues to do this, it’s likely it needs a new transmission, gears / shift dogs and shafts. That will suck…

The other things I installed today were simpler handlebar risers, and a Honda Grom clutch perch and lever set up. The later is intended so I can use the same spare replacement parts on multiple bikes (Grom, z125 and Benelli) without having to keep unique parts for each. The set up also lowers the handlebar about 1 inch as well. I don’t know if that’s helpful to anybody or not. This change does make it easier to repair handlebars or levers in the event of a crash. That’s just due to simpler parts.

The last work, that I ran out of time for, was to flip the tires. The left sides are completely worn out on the back. There’s decent rubber left on the right side. The track we regularly ride is mostly left-handed. That’s how the tire got the way it is. It got dark here too early and I couldn’t continue working. I will have to wait a while to find time when I can be in the garage for another hour to flip the tire and reinstall the wheel. I’ll wait till after I ride the bike to find out if there’s other work I need to do at the same time. I need to be more efficient with the very limited time i have outside of my regular job.