There isn’t a lot of info posted out there so I am going to post what I know or have found out trying to hop up my daughter’s 2015 Kymco Mongoose 300. We ride sand, so the mods I have done may vary from others needs.
1. The stock sprocket is a 38. Kymco has a 40 tooth rear that can help turn sand paddles a little easier.
2. Through EPI, having them look up the DVX 300, a maroon torque spring is available with 3 purple clutch springs that fit into the secondary unit. The primary stock roller weights are 25 grams. The dimensions are 23x18. I replaced them with 20 gram weights. It wakes up the clutch/bike tremendously. Now it will spin paddles
3. The Countershaft sprocket can be replaced with different sizes. I believe stock is 14 tooth. Planet racing has a 13,14, and 15 available. Stock with paddles, clutch, and 40 tooth rear sprocket work well in sand.
4. The stock exhaust sucks and is restricted. HMF and planet racing sell exhausts. An exhaust makes it smother and more powerful throughout the power-band.
5. With the stock constant velocity carb you can’t take the air box lid off. So I ordered a Mikuni 32 VM carburetor, right side idle. There is a two and four stoke model, and I can’t remember which one is which. I think the 32-33 is the four poker carb. I’ll have to look at mine. To get it to fit in the stock intake boot I had to take a millimeter off the front to get it to fit. I could of bought a new rubber Mikuni intake boot but became impatient. I used a Terry’s trx 250R throttle cable with a 90 degree bend and threaded to make it low profile. There is not much room between the tank and the top of the carb. Then you’ll need to get a new 2 1/8 diameter hose from the carb to the air box. I temporarily flipped the air box boot and it fits the carb and the air filter. There’s a gap around the boot and air box.
PJ Motorsports sells a carb kit, yet the stock choke cable isn’t long enough to fit the Mikuni carb. Paul is the owner and his kit would work. Now it runs great without the air box lid. I need to see now if I can eliminate hoses.
6. Web cam does a regrind for the Arctic Cat DVX 300 and Mongoose 270/300, but you have to send you cam in. Naraku makes a cam shaft they sell through planet racing USA. The Naraku cam says it will only work with their top end. I emailed Naraku and they said this isn’t true, that it would work on a stock motor. The only thing about putting in a cam is bumping up the compression and I don’t know if anyone offers a higher compression piston. I think I am going to buy the Naraku cam in a couple of weeks to try it out on my daughter’s Mongoose 300, so I let people know what I find out.
