Alright, let’s talk about squeezing some extra juice out of the old KX85. The goal? More horsepower! It’s not gonna be a walk in the park, but we can definitely make this little beast scream a bit louder.
First off, I started by tearing down the top end. Gotta see what we’re working with, right? Checked the piston, cylinder walls, the whole shebang. Everything looked pretty decent, but “decent” ain’t what we’re after. We want “awesome.”
Next up, the porting. This is where things get interesting. I spent a good chunk of time with a die grinder, carefully reshaping the intake and exhaust ports. Now, I’m no expert, so I took my time and followed some guides I found online (use at your own risk, kids!). The idea is to smooth out the flow and increase the area, letting the engine breathe easier. It’s messy work, lots of aluminum dust, but hey, no pain, no gain!
After porting, the next step was addressing the exhaust. The stock pipe is okay, but it’s definitely a bottleneck. So, I slapped on an aftermarket pipe and silencer. This made a noticeable difference right away, the engine just felt freer.
Then came the jetting. With the increased airflow, the stock jetting was way off. It took some trial and error, but after a few hours of swapping jets and reading the spark plug, I got it dialed in pretty well. The throttle response was crisp, and the engine pulled hard throughout the rev range.
- Main Jet: Swapped from a 142 to a 148
- Pilot Jet: Bumped it up from a 45 to a 48
- Needle Position: Raised the clip one position (lowering the needle)
Finally, I decided to mess with the timing a little bit. I advanced the timing a couple of degrees, which gave it a bit more snap off the bottom. Be careful with this though, too much timing and you’ll be detonating like crazy.
The Results? Well, I don’t have a dyno, so I can’t give you exact numbers, but I’d say we gained a solid couple of horsepower. The bike feels noticeably faster, especially in the mid-range. It’s more responsive, more fun to ride, and that’s what it’s all about, right?
It wasn’t easy, and I definitely learned a few things along the way. But in the end, it was worth it. Now, if you’ll excuse me, I’m gonna go rip some laps!
